Who wants to play; Find the problem?

[Chris(NJ)]

Here's where I'm at. About a month ago S*** hit the fan w/ this truck lol. Seems like everything happened at once and I find it hard to believe that that 3 separate problems occurred simultaneously. So if I was a betting man, I'd assume they're somehow related. But knowing how bad I am at gambling, they're probably not related.

Overall, The truck has been pretty flawless over the past 14 months. So it's not likely a tuning issue. Motor is a crate 350 w/ a th350 trans. Ran the edelbrock carb serial number and came back to a 750cfm, (1407)

I noticed a slight stumble driving it to a cruise night. I thought maybe another arching plug wire, maybe some bad fuel...but nothing that grabbed my attention enough to think there was a major problem.
Leaving the cruise night things got bad quickly. I thought the truck would die and kept putting it in neutral at stop lights in fear of it stalling.
Limped it home and parked it in the garage.
Pull it out of the garage a few days later and you can see the mess it left on the ground. Both trans and engine oil leaking.

The engine problem is definitely worse in gear. Reverse, drive, etc...it runs, but barely. If I step on the gas, it really doesn't want to move. but idle doesn't seem THAT bad. I guess it's all relative. When we had warmer weather, It also seemed to get worse as it heated up. No scary sounds either. Engine itself sounds smooth. No knocking, tapping, etc. It's just...missing.
I pulled the distributor since it's been over a year of driving. I wanted to see how it looked, and figured I'd replace the ICM while I was in there. Read that can cause similar problems to what I was experiencing, but no dice. Unchanged. Spark plugs looked fine from what I can tell. No major tell tale signs of a problem.

Ideally, If the problems aren't related, I'd like to fix the flat-on-its-face stumble first. Because I can always add oil to get it to a mechanic and if there's a few leaking seals, that's going to be beyond my capabilities to fix anyway.

I know this is almost like taking shots in the dark, but I'll take any advice I can get.
Believe it or not, this is my first carb'd motor. I've always worked on modern engines, and I'll never underestimate the value of being able to plug into an obd port and have a computer tell me what the problem is

Old pic of motor, but nothing really different.

[nvrdone]

id start checking electrical - check for loose grounds & alt output. if its a bad ground that could cause a stumble. if the alt isn't putting out that could cause the ignition to not have enough juice to get a good spark. good luck

[bobinbc]

I had a bad stumble and it turned out to be fuel filter. Check the easy stuff first lol. I would also check for vacuum leaks, esp. hose to modulator valve on trans.

[Rickysnickers]

As far as the tranny fluid goes, I'd check the rear output seal, where the driveshaft slips into the tranny. I can't tell which side your engine oil dipstick is on, but check that for leaks. The other stuff, no idea. I cannot give any advise, sorry.

[dwcsr]

The plug has oil on it above the sealing ring, that may be your engine leak from a valve cover, to much pressure in the engine, some other reason? should be easy to find just as the trans should be easy to find. once you know what's leaking you can determine why or if it related.

I would look at fuel first, fuel issues tend to creep up on you like you describe. Electronics usually is some un explained issues then it dies.

Checking grounds as mentioned above is also a good idea whenever you have unexplained electrical issues. Bad grounds can create odd issues and electricity will find a ground if one is available and sometimes its through another device that's not equipt to handle grounding of another circuit. Ohm the engine to distributor to see if its grounded. a distributor ground sometimes ends up being through the oil pump. not good, run a ground strap to it if needed.

A vacuum gage will tell you a lot about what's happening as far a the engine and valve train. A Stoich meter (Air/Fuel) will tell you about the fuel leaving the engine, if its burning correctly, if you lean or rich. Using both also helps you dial in the jetting and confirms you have the valves adjusted properly. You'll be surprised at how much easier it is to tune with those two meters and how much better it runs afterward.

[dwcsr]

Originally Posted by bobinbc

I had a bad stumble and it turned out to be fuel filter. Check the easy stuff first lol. I would also check for vacuum leaks, esp. hose to modulator valve on trans.

I hadn't thought about the modulator but on my TH350 there were several threaded holes on the right side that were leaking , one was the kick down cable, one was where a spark control was screwed in and broken. Modulator O rings on those always leak at some time

[dsraven]

check the vacuum operated shift modulator, they can leak internally and cause a vacuum leak from the engine (causing the idle and driveability issues) and also can leak externally (trans fluid).
as far as the engine oil leak, a spot on the ground isn't going to help us help you find a leak. we need a pic of the engine. that said, wash the engine off, run it till it leaks, then check where it comes from. follow the leak from bottom upwards till you don't see any more oil staining, then the highest point is usually the start point. valve cover gasket, distributor base gasket, intake gasket or rubber/silicone seal in the valley area, front or rear seal, timing cover, oil gallery plug behind flex plate. many options without a more definate location.
check pcv and breather system for blockage as well because that will allow engine to pressure up and can blow oil past a seal.
check for "gummy" vac lines because they can suck down and flatten out if soft, then stick together.
post up a pic of what your engine looks like and where the leak is (front, rear, left, right?

[Chris(NJ)]

Thanks for the ideas guys. @dsraven, sorry...I know the leak on the ground doesn't show anything. It was more for reference to show how much leaked out in a matter of a couple days. That amount is normal now. If I pull the truck out, wipe off the ground and park it...that same amount is back on the ground the next day.
From what I can tell, the engine leak is from the front, driver side. But that's solely based on where the leak is originating. I did my best to look at the trans for a leak, but I'll be damned if I can find a specific area where it's leaking. I was able to grab the driveshaft and I can wiggle it slightly. That didn't seem normal to me. But maybe a little wiggle room is normal on this trans?

Sounds like the vacuum modulator is a common culprit. Looks like it is on the right rear side of the trans from my brief google image search. I'll check that out for a leaking vac line first, but will order a new one in the meantime. A few of the symptoms of a bad valve match up. Including some smoke out the tailpipe. Normally I would always get a little bit on startup, but lately it's been continuing longer at idle. I assumed that was from it sitting longer and not burning off since I haven't been driving it.

[mr48chev]

Pull the hose off the modulator and see if there is fluid showing. There shouldn't be any. For once every piece of advice you got is good advice with no wags thrown in. I'd go along with BobinBC and check the easy stuff first and along with checking the modulator change the fuel fiter (s) .

On the fuel and fuel filter thing I am picky as all get out as to what stations I buy gas at. I usually go to a local newer high volume station or Costco and try to never go to those old used to be a gas station now are a mini mart stations. If you stopped at a station that might not keep their tanks clean and water free that might be part of the issue.

Do the simple things and only make one change at a time. Guys all too often try to make several changes at once tracing a problem and never do figure out the problem. The "it's got a miss so I'll go buy this, that and those other things and change all of them hoping I fixed it." syndrome.

[Jesse Z]

Also check your PCV system. If the valve clogs it can affect your air/fuel ratio making the engine run poorly, and allow compression pressure into your crankcase to blow oil out of every orifice.

[Softpatch]

smell you motor oil at the dipstick .?
Does it smell like gasoline.?
is your choke set up right for the Temp outside
Set up for summer driving set up for cooler weather Diffrent setting....

[mr48chev]

They run like crap when the pvc hose swells up and gets loose because the hose the bonehead at the parts house sold you wasn't a hose that held up against oil or oil fumes. Just had that happen on the 454 in my dualie on a hose less than a year old . I'm not sure what that hose was intended for but it sure wasn't for a PCV system.

[dsraven]

good point softpatch, if it is over fuelling, from a bad choke set up or carb inlet needle and seat or whatever, then it will get into the fuel and dilute but also make it easier to find a leak. if the oil smells like fuel then don't start the engine till the oil is changed. the fuel vapors in the crankcase can ignite and blow the tin work off or at least distort the valve covers and possibly make the seals leak or, worse, start a fire that burns the truck down. not trying to be a downer here, just warning you.
try some brake clean to clean off the engine, let it sit to dry and clear the ambient air of fumes (yes, flammable), then start it up and check for wet spots where the oil is starting to leak out. if you find nothing then let it sit and come back with a good light when it has had a chance to leach out.
leak spots:
-valve cover gaskets, sometimes, if aluminum especially, the cover doesn't fit the head well and the gasket will leak prematurely due to poor fitment.
-intake manifold gaskets and the silicone or rubber seals that go in the area between the cyl heads. some are simply silicone caulking or cheaper grade of auto silicone (home done jobs) instead of automotive grade and that type may deteriorate due to contact with the engine oil. if you end up re doing that seal use "the right stuff" brand and you will not usually have any more problems with that area. ensure the surfaces are clean and dry before squeezing on the silicone and let the silicone cure before adding oil.
-distributor base gasket
-timing cover gasket and cover in general. I have seen where the chain has stretched and worn a hole in the cover.
-front engine seal.
-vibration damper bolt/washer. a leak here is usually easily fixed with removal of the bolt, clean with brake clean or similar, rtv silicone on the back side of the washer where it seals against the dampener and install/torque. make sure the damper is bottomed on the crank first. there is a tool for that, no hammering. it is a stud that screws in and then a nut pulls the damper on all the way. tool is then removed and the proper bolt/washer installed.
-silicone or rubber inserts in the oil pan at the front where the pan meets the timing cover. again, some are just silicone. also check the area at the front of the oil pan corner where it arches over the timing cover. there should be a dab of silicone there to prevent leaching through the area where 2 gaskets meet.
-fuel pump cover gasket and fuel pump gasket or block off plate gasket. also, on the front of the block there is a bolt hole that is drilled through to the bore for the fuel pump push rod. this bolt can be replaced with a longer bolt to hold the pushrod in the block when swapping the fuel pump out. ensure the proper bolt is in there and that bolt has some sealer on the threads and/or a copper washer under the head of the bolt, which should be a short bolt whose head bottoms against the block to seal the copper washer but is not too long so it drags on the fuel pump push rod.
-engine oil pressure sender.
-engine oil pan, ensure all the bolts are tight but not over tight because that can cut the gasket.
-oil pan plug. check the threads in the pan and ensure the plug is installed so the head of the bolt is square with the pan sealing surface. also the plug needs a copper washer or gasket of some sort. there are steel washers with oil resistant rubber sealing surfaces that work well to seal.
-rear oil gallery plugs. these will look like a rear main seal leak because they are behind the flywheel/flex plate.
-rear main oil seal. this will likely be dripping out of the drip hole in the torque converter cover and also may show dampness around the starter area. if the torque converter cover is removed you can usually see up in there enough to tell if the seal is leaking.
-the dipstick tube connection to the block. pretty common to have a crack in the tube near the block
-the transmission vent
-trans cooler line fittings and tubing. the fittings can simply be leaking at the threads or they or the cooler lines can also be cracked from flexing of cooler lines or stress on the lines or from unsupported lines. if you have the flared fitting style of cooler lines a flare could also be cracked or the fitting sealing surface may be marred so a seal is hard to achieve.
-the shift modulator valve or mounting seal could be leaking. remove the vacuum line and check for trans fluid in the vacuum hose and/or inside the modulator valve. there should be no oil inside the vacuum area of the valve or inside the vacuum hose.
-the governor housing gasket/seal (that is the domed looking thing near the rear on the driver's side. held on with a bale wire and sealed with an "O" ring.
-the shifter shaft seal.
-the transmission oil pan gasket and drain plug (if equipped)
-the dipstick tube seal in the trans housing. also, the support bracket that holds the dipstick tube to the bell housing is spot welded to the tube. a crack here can cause a leak. fairly common since nobody is all that careful with the tube and the welds get torn a bit but not enough to tear the bracket off the tube.
-the seal at the rear of the trans where the driveshaft goes in.
-the front seal of the trans where the torque converter goes in. possibly seen when the tin cover is removed. there is also a pump housing seal in that area that could be leaking.
-a leaking torque converter due to a crack or poor weld of the front and rear halves of the converter or a pinhole in the converter. some trans shops will drill a hole in the converter to drain the converter and then install a short screw afterwards. these can leak. I have also seen converters with drain plugs.
-the speedometer adapter to trans housing seal or the shaft seal inside the adapter.
-the seal for the tail shaft housing to the main body of the trans.
-check for a crack in the trans housing or a porous housing which can leach oil through. never seen a housing porous enough to leak but heard of that before.
-check all the trans pressure port plugs for leakage.

that should get you started, haha.
it's all I can think of that would possibly leak. good luck. post some close up pics if you get a chance.

[Chris(NJ)]

Thanks guys!
@Jesse_z...coincidentally, I bought a new pcv valve yesterday. For $8, it's worth replacing to see if theres any change.

@Softpatch, I haven't smelled the dipstick but I'll give that a whiff today. Unfortunately the problem started well before the change in weather.

@dsraven, thanks for writing all those recommendations out! I'm hoping the weather warms up a little bit for the weekend. By the time I get out of work during the week, it's dark and my garage is so small that I can't jack up the truck in it. I need to pull it out of the garage to work on it. So I need daylight and at least some weather in the 40s lol.
So hopefully I can knock out some stuff this weekend coming up and will snap some pics along the way.

[tmoble]

clean the engine as best you can and add the fluorescent dye available at most auto parts stores. they usually also sell the black light flashlights used for the inspection. Or try Home Depot or Lowes or whatever if they don't. check right away after adding the dye, otherwise the dye will get spread around and you're back where you started.

Lots of good info in Ravens reply.

Same technique for the tranny. might want to try it first lest dye from the engine gets all over it. Popular leak point on tranny is the o-ring or rubber bootie for the dipstick tube.

[FiftyTwo]

Lots of good ideas have been brought up to check, so here's a couple more.

Check the vacuum advance canister on your distributer. A bad diaphragm will cause a vacuum leak and a crappy running engine. Stuck advance plates, or broken return springs will also cause your engine to run poorly. Very easy to check. Good luck.

[57chevyman]

my truck was running great and then without warning it stalled out at a light and i thought i ran out of gas. i had half a tank tho. i got it started and it would barely run. i have a 350 engine and edelbrock carb. in my case it turned out i needed the carb serviced and adjusted including replacing the rubber caps that were getting dry and cracked. i replaced with better vinyl ones.

[dsraven]

for the poor running
does it smell like over fuelling or under fuelling (oxides of nitrogen make your nose burn), check the usual carb stuff, loose mounting bolts, plugged float bowl vent, etc. check all the tune up stuff, which includes vac lines, and also check the distributor centrifugal advance to ensure it works and is not stuck or seized. if you can get it running in the darkyou can check for a bad plug wire by seeing if there are sparks anywhere frma plug wire. sometimes the wires will arc to their neighboring wire if it is an easier pathway to ground.

check, on running engine:
vacuum at idle
base timing and timing variance when revved up-should change-disconnect vacuum advance and check if timing changes
adjust valves and check all rocker studs to ensure they are all at the same height-indicates if a stud is pulling out of the head. check all valve springs to ensure there is no broken ones, check the pushrods for straight, check for any valves that seem to be taller than others-indicates a valve issue=possibly a burnt exh valve.

check,on cold engine
compression dry
compression wet
cyl leak down test
plugs
plug wires
distributor cap and rotor, also the spring loaded rubbing block in the centre of the cap
coil (for discoloration(overheated) and ground strap
turn engine backward 1/2 a turn, mark rotor position and crank position, then turn the engine the normal direction while watching the rotor. stopas soon as the rotor starts to turn. now check how far the engine turned before the rotor turned. that will give an indication of the slack in the timing chain and gears
pcv valve and vac hose,include the fresh air supply hose and filter
fuel,for freshness and contamination/water etc.
fuel filter- cut old one apart to check for what is inside it for dirt
any rubber fuel hoses and steel lines for cracks, kinks or flat spots from road debris
ground strap from battery to engine
plug in for power to the distributor

if all good start up and adjust carb, timing etc like you would if doing a tune up

[Chris(NJ)]

No diagnosing this weekend. Didn't have the time to work on anything and I need to get some tools to test vacuum, timing, etc. but I did pull it out of the garage real quick to snap some pics. Looks like things are getting worse and I'm not even driving it. Now I noticed that the coolant has managed to start leaking! It's like every system has built up pressure and is pushing it's fluids out! WTF! Also seemed to be running worse than the last time I started it. Anyway, heres a few more pics to add to the story.

Oh, and Raven;
I previously tested the plug wires to make sure they were all w/in range of each other. high values, but all consistent.
Plugs and pcv valve are new.
Cap/rotor looked good too.

Coolant leak! (Also had some oil up there too, but that has always happened since I've owned the truck).
Trans; easy to see some leaks from the speedo cable, rear seal and....drain plug? I didn't see any sign of it leaking from up top. Also didn't see any leaks from the side near the modulator valve or other ports. Fwiw, that modulator valve has a full tubber vacuum line. No hard line between the plenum and valve. It was also zip tied pretty tight so I didn't bother cutting it off yet to see if there was any oil in the vac. line.
Engine leak? No clue yet. Still can't see an obvious point of origination.

Hopefully I can find some answers soon to update this thread w/ more than just the new problems

[Chris(NJ)]

Let me add an update to this....I got to work on it a little bit this weekend.
I took a bottle of carb cleaner and started to spray around. Didn't take long to find the leak. It was the whole intake manifold! (and later find out the exhaust manifold bolts, valve covers and the carb bolts were loose too). I looked up the torque numbers and torqued them down(25#, which seems low but whatever). Immediately got my idle and driveability back. I was super excited. I had to call it quits for the day because it was Thanksgiving, but on Friday morning I took it out for a 10 mile drive and in a complete turn of luck (or fate) as I'm a couple blocks from home.... I'm making a right turn, get a loud knock that I write off as suspension noise (happens on that turn every time) and as I accelerate out, the stumbling is back. WTF

So now I'm lost again. Oh, and for what its worth, that trans and coolant leak stopped after I torqued the bolts down. I have no idea if it's somehow related but coincidence seems to say so.

I double checked all the bolts again. All good. Also sprayed the carb cleaner again and that checked out ok.

The only new thing that has developed is that it would almost appear as though I have an exhaust leak now. I'm getting some smoke out of #8 exhaust port. Or at least it looks like it. I didnt drop any oil or anything back there that'd burn so this is the only logical solution.
Do you guys think that knock that I've heard could've been some offsetting geometry between the suspension and exhaust/engine, pushed the passenger side exhaust in some strange direction and cracked the manifold. Or maybe just the gasket. It's not like the truck is surviving on a lot of back pressure to begin with. There's no catalytic converters. So I wouldn't think theres a relation between the exhaust leak and driveability.

The truck is also surging more than last time. That's about the only difference. Otherwise, It still wants to die.

I'm ordering a vacuum test kit today. I thought I may have had an old gauge laying around, but turns out it's a pressure gauge and not vacuum.

Engine oil is still leaking. Havent gotten around to that issue yet

[dsraven]

before you start the engine again, pull the dipstick and check the oil. if it has ANY chocolate milk look to it then you need to pressure test the coolant system. also remove the oil filler cap, flip it upside down and look for a milky residue or a lot of condensation on the under side. this indicates a coolant leak into the engine oil. if this is the case it is not going to be long until your engine bearings go south. if your intake gaskets were leaking to the exterior then they were also probably leaking to the inside of the engine. you could also try cracking the oil drain plug-on a cold engine that has sat over night-to see if there is any water that leaks out before the oil starts to come. that is a tell tale of a coolant leak for sure. a small coolant leak will possibly not show up as cloudy oil on the dipstick. an oil change into a clean container would show it better. like said, if the intake bolts were loose then the gaskets are likely soft and possibly leaking or torn from the intake shifting slightly as the engine runs and things move from vibration and expansion/contraction and the pull on the throttle cable etc. the intake ports can pick up oil sprayed under it in the lifter valley if the gasket is bad, possibly causing the oil burning and poor running-inability to get a constant tune.
because you intake bolts were not tight I would say, for the money and time invested, just replace the intake gasket set to be sure your gaskets aren't torn or soft/leaking. (felpro gaskets and a good sized bead of "the right stuff" silicone for the valley ends-not the formed or cork gasket there) while you are in there you can check the block in the valley area to ensure it isn't cracked or anything (look in the area above the lifters for a spot that just won't dry up like the rest of the area while cleaning. you may need some varsol or brake clean to get the area to dry, but remember they are flammable so do this with the oil pan plug removed and allow to dry thoroughly). you can also replace the distributor base gasket while it is out and check the bushings and centrifugal weights and springs etc-maybe even a recurve to set the base and max advance while you're there. check the oil pressure sender and fitting, if equipped, for leaks and/or cracked fitting. you will end up with the piece of mind that it is right plus probably solve your vacuum leaks and possibly your oil leaks. the engine may then be tune-able. remember when you remove the intake/carb that the carb needs to stay right side up so any nasty stuff in the bottom doesn't get into a spot where it will cause issues later

[dsraven]

forgot to mention that the carb cleaner test for a vac leak only tests the gasket/sealing area for leaks on the OUTSIDE of the intake to head gasket area. it doesn't test for a leak on the under side of the intake to head sealing area. this area could be leaking and drawing in engine oil as well as leaking coolant into the engine.
if you end up removing the intake for new gaskets, run a straight edge on the intake gasket flanges to ensure they are flat and straight. also check the head surfaces for pitting or non-flat surfaces.
you may want to replace the intake manifold bolts at the same time and when torquing them down ensure to do it in steps and in the proper sequence as per the sheet that comes with the gaskets. this ensures the gaskets don't move as you tighten things down. a set of removeable line up studs can be a help as well, or some tapered line up punches that you can drop into the bolt holes for alignment and then remove as you put the bolts in place.
set the clean intake down into place with no gaskets and check to ensure the angles are correct against the heads. if the heads have been planed down then the angles/gasket space may be off enough to cause a leak or cause the bolts to back out.
replace the carb base gasket and check the mounting flange to ensure it is still flat. torque the bolts in steps and to the proper torque on install. it doesn't take much to warp the carb base.
check the carb throttle shafts for wear. they can leak vacuum around the shafts and also land in a different spot each time after throttle movement. this causes a "hard to adjust" idle issue because the butterflies don't sit in exactly the same spot each time which means they effectively change the throttle opening slightly each time. this was a real problem with old rochester 4 bbl carbs. lots a shop time has been spent on drilling and bushing the throttle shafts on those

betcha that would fix a whole bunch of your issues at the same time. loose intake bolts was the give away. soft/torn intake gaskets is the usual result. oil and coolant leaks as well as steam in the exhaust, oil burning and milky oil are the symptoms. engine failure can be the final result. worth a good look at least-with a pressure tester on the cooling system for sure.

[dsraven]

also, do yourself a favor and get a steel washer style pan plug for the trans. the ones that have a neoprene rubber coating on the washer. install that on the trans plug. the plastic oil pan plug gaskets are always prone to leakage and over-tightening of the plug.

[dsraven]

if you end up doing the intake gaskets, pull that thermostat out and redo the gasket there as well. if you don't already have one, install a gm branded (ac/delco) thermostat. one with the little check valve looking thing in it. that allows air to be purged better and also any steam can get past the stat through the little hole. install the hole side in the highest point (so at the front normally) so air can purge through. personally i have changed lots of stats over the years and will use nothing but OEM parts there. thats how much trust I have in the aftermarket stats working correctly for any length of time. also, check that the stat fits the recessed area of the manifold/stat housing so the gasket has a chance of sealing correctly and the housing doesn't crack when torquing down the bolts.

[dsraven]

on that front end knock on turns, check to ensure the control arm bolts are tight, the ball joints are tight, the tie rods are tight and not bottoming against a frame that maybe shoudda had a C notch, the steering rack is tight and, if you have one, check the steering stop interference with the spindle. some have an adjustable bolt that stops the spindle from turning past a certain spot at full turn. it bottoms against a flat spot that is sometimes not flat so when the steering is turned to the stop point and the suspension is also going over a bump the stopper bolt is forced out of it's rabbit hole, or low spot, and can make that bumping noise. some front ends rely totally on the rack for maximum turning. anyway, better find out what the problem is sooner than later. don't wanna find out the hard way, loose control, and be looking at the grass from the bottom side.....
got a pic of the front end, maybe a couple of pics so we can see both sides and the rack? could it be a spring that doesn't fit into the spring seat well and is moving? usually a tell tale is a bit of rusty powder in the area, that denotes something is moving metal on metal.