1987 k20 TBI Starting Problems. I know another "starting problem" thread

[WuchaGot]

Howdy folks, New to the forums and just picked up my first Chevy truck and having some issues and looking for some advice.

I picked up my uncles old farm truck that was garaged about 5 years ago when my uncle bought his new truck. We rented out the house that the truck was stored at 2 years ago and the truck was moved outside. When it was moved it started right up and they used it for a harvest then it was parked outside with the trailers where it has sat for 2 years.

I bought a new battery 2-3 weeks ago and hooked it up, sprayed some started fluid in the throttle body and after about 3-5 min of working at it got it running and it sounded good. I did a full maintenance a couple days after I got it running (new cap, rotor, plugs, wires, oil change with synth blend and a bottle of lucas, auto tranny filter, lucas branded tranny fluid, thermostat and coolant temp sensor)

It was a VERY hard starter the first week but it began starting easier so I figured it had just been sitting and was a little stiff and running it would be good for it. When I drove it and shifted it into drive or reverse it would bog down a lot, sometimes it would bog and die other times it would bog and recover. When I drove it and pressed the accelerator it would sometimes roar down the road with tons of power and other times it would choke and die. 2 weeks ago outside temps started dropping into the 30s and I went out to start it and it would crank but for the life of it it would not start.

I know all the sensors and modules make changes based on temp and little things can cause big issues and the bogging was making me think fuel issues, it had been sitting for a while so the fuel could have been bad. I pulled the fuel filter and blew through the inlet and could hardly blow through it so I replaced it. I changed a bunch of clogged vacuum lines but 2 ports on the throttle body were gummed up solid so I took the throttle body off and did a FULL clean up and rebuild (Fuel pressure regulator, new idle air control valve, new rings, seals and gaskets. I used the same injectors, they were fine). I had my wife crank it over while I shot a light at the injectors and they were spraying nicely so fuel is no longer my issue but still wouldn't start.

Now I am looking at ignition issues I guess. Any advice or typical issues with this make model that are common? I have ordered a new ignition module and coil. I am also reading that the ECM can go bad. My wife is pissed. Bought the thing for $700 and already put $500 trying to get it running and she is thinking I bought a lemon. LOL

My uncle is a maintenance fanatic and wont let the oil get near 3k miles old before changing it and because his vehicles are important for his livelihood it's cheaper for him to spend money to maintain his equipment then to loose money because his equipment goes to heck in the middle of harvest. He parked the truck with a fresh oil change and blocked the wheels so the tires wouldn't decay. He had the engine professionally rebuilt about 53k miles ago and the tranny serviced before parking it. The fluids were all as clean as if they were just changed the day before but I changed it all anyways.

Thanks in advance for any advice. God Bless

[Don SC]

Did anybody disconnect the oil pressure sending unit? If the em doesn't "see" a signal from there, it will not start.

[WuchaGot]

I wouldn't think so but when you get to working things happen. I would guess it would be behind the distributor on the driver side but the only thing I did around that area was when I changed the distributor cap and rotor but the truck ran for a week after that. I could have bumped something when I took the fuel lines out to remove the TBI. I think the fuel lines run in that area. I will check.. LOL.. Thanks for the suggestion.

[WuchaGot]

I went out and I didn't see a oil pressure sending unit where I thought it would be, or at all for that matter, maybe I am thinking of something else. I was looking for a round cylinder with a sensor plug coming out one end. I went and checked all the connectors to see if there was anything else I missed and everything seems connected. For the heck of it I cranked it over for a few seconds and it hiccuped for a second like it was going to try and start so I cranked it over a few more seconds and it chugged to life. I put it into drive again after it ran for a few min and it bogged down and almost died so I feathered the accelerator and kept it alive. It stayed at high idle for 10-15 min so I went and held the accelerator down about 20% for a 10-20 seconds and let off and it idled down. After it idled down I put it into drive again and it held its idle without bogging down at all.

[hatzie]

I think the oil pressure cutoff sensor is down by the oil filter housing.

[Don SC]

hatzie, that's the secondary location for the sensor. The primary location is in the rear of the intake right next to the distributor. It's common to see it using the same fitting as the oil pressure switch. The switch has 2 wires. The sender has only one wire- typically a tan wire, which goes to the ecm.
Anyway since the truck has started again, the cancels out a bad oil sender.

[rfmaster]

Originally Posted by WuchaGot

I went out and I didn't see a oil pressure sending unit where I thought it would be, or at all for that matter, maybe I am thinking of something else. I was looking for a round cylinder with a sensor plug coming out one end. I went and checked all the connectors to see if there was anything else I missed and everything seems connected. For the heck of it I cranked it over for a few seconds and it hiccuped for a second like it was going to try and start so I cranked it over a few more seconds and it chugged to life. I put it into drive again after it ran for a few min and it bogged down and almost died so I feathered the accelerator and kept it alive. It stayed at high idle for 10-15 min so I went and held the accelerator down about 20% for a 10-20 seconds and let off and it idled down. After it idled down I put it into drive again and it held its idle without bogging down at all.

Based on this description you have classic low fuel pressure problem. TBI systems require 9 to 13 PSI to operate (they work much better at 14 to 16 PSI but that's another story). Most of these trucks are approaching 25 years and if you have OE fuel pump it is probably toast. Another common problem is a section of fuel line between fuel pump outlet and feed through. It rots and over time leak develops. Today gas is a nasty mix of chemicals and ethanol which eats up old rubber based fuel lines. Recommendation - perform a fuel pressure check - you can do it at the fuel filter and if Fuel Pressure is less than 9 PSI it is time to drop tanks and R&R Fuel pump and hoses (Use SAE 30R10 rated hose)

Side note. Contrary to popular believe Fuel pressure switch does not cut off fuel pump. It is used as a back up (fail safe) for a Fuel pump relay so that if relay contacts fail while engine is running the oil pressure switch will keep fuel pump operating. Oil pressure switch closes its contact once oil pressure exceeds 4 to 7 PSI. Fuel pump relay is controlled by ECM and it will energize FP relay once its begins to receive DRP pulses from ICM in the distributor. Since your injectors are spraying ECM is receiving DRP pulses from ICM.

//RF

[WuchaGot]

Originally Posted by rfmaster

Based on this description you have classic low fuel pressure problem. TBI systems require 9 to 13 PSI to operate (they work much better at 14 to 16 PSI but that's another story). Most of these trucks are approaching 25 years and if you have OE fuel pump it is probably toast. Another common problem is a section of fuel line between fuel pump outlet and feed through. It rots and over time leak develops. Today gas is a nasty mix of chemicals and ethanol which eats up old rubber based fuel lines. Recommendation - perform a fuel pressure check - you can do it at the fuel filter and if Fuel Pressure is less than 9 PSI it is time to drop tanks and R&R Fuel pump and hoses (Use SAE 30R10 rated hose)

//RF

Thanks for the info. If it is still a fuel then it would have to be at the pump or with the lines as everything else is new or rebuilt as of this past week. I did visually inspect the spray from the injectors after I changed the fuel filter and rebuilt the TBI and it looked like a nice even consistent flow but I doubt you can tell fuel pressure from the injector spray.

What would I need to test the PSI with?

Update to my last update. I tried starting her up yesterday and today and no dice. Cranks but wont fire. My new ignition module came in today and my new coil should be in tomorrow. I will change those out for the heck of it.

Thanks for the advice.

[rfmaster]

1) Before swapping ignition control module - ICM. When cranking - spray a little bit of fuel into TB. If it burps and fires up then its a fuel delivery problem.

2) To measure Fuel pressure you need a fuel pressure gauge - For example Actron CP7817 or equivalent

[motornut]

Can you always hear the pump,after turning the key,before cranking
I replaced my 87 pump,cause it died on the road,I couldn't hear it run
replaced it and got stuck again ,ran a temp wire,worked fine,traced the power wire
found the power out @ a "green" corroded hard baked cut over the rear wheels

[WuchaGot]

Originally Posted by rfmaster

1) Before swapping ignition control module - ICM. When cranking - spray a little bit of fuel into TB. If it burps and fires up then its a fuel delivery problem.

2) To measure Fuel pressure you need a fuel pressure gauge - For example Actron CP7817 or equivalent

Thanks for the info on the pressure tester, found it on Amazon for $38.

Far as priming the TBI for a test start, I have done that a few times with a can of starting fluid and no dice. I have tried starting fluid before changing everything out and after changing everything out and it has not helped start the truck at all. I have use starting fluid and cant get it to start at all then I try to crank it over and start it with no priming the next day and it starts on its own. I just started it today and practically started right up and drove like a champ, it was a warm day today. The temp out side seems to be the key.

30-40 degrees outside and it wont start 50-60 degrees and starts fairly easy.

[WuchaGot]

Originally Posted by motornut

Can you always hear the pump,after turning the key,before cranking
I replaced my 87 pump,cause it died on the road,I couldn't hear it run
replaced it and got stuck again ,ran a temp wire,worked fine,traced the power wire
found the power out @ a "green" corroded hard baked cut over the rear wheels

If i turn the key on but do not turn the engine over I can hear the pump for about 10 seconds then it stops. If I start the truck I can always hear it. Its not as if I can hear it easily in the cab but I have put my ear near the tank while it was running to listen if I heard it pumping and its humming away.

[rfmaster]

Originally Posted by WuchaGot

Thanks for the info on the pressure tester, found it on Amazon for $38.

Far as priming the TBI for a test start, I have done that a few times with a can of starting fluid and no dice. I have tried starting fluid before changing everything out and after changing everything out and it has not helped start the truck at all. I have use starting fluid and cant get it to start at all then I try to crank it over and start it with no priming the next day and it starts on its own. I just started it today and practically started right up and drove like a champ, it was a warm day today. The temp out side seems to be the key.

30-40 degrees outside and it wont start 50-60 degrees and starts fairly easy.

In this instance it is a process of elimination.
You must have spark during cranking. No spark would indicate a problem with ignition system - usual suspects should be checked: reluctor coil, ICM, distributor cap, rotor, coil, spark plug wires, spark plugs. Coil and ICM must have +12 volts during cranking (pink wire). Grounds should should be cleaned and oxidation free.

Just take one step at a time and you'll find it. Intermittent nature of no start would lead to believe that this problem is electrical.

//RF

[tucsonjwt]

Before dropping big $$$ in this truck, I would take it to a mechanic with a modern shop equipped with modern diagnostic tools. Spend $70-$100 on testing and avoid a lot of wasted dollars. You can do the actual repair yourself, just get a good diagnosis first. My $.02. My guess is you only need something minor.
-

[rfmaster]

Originally Posted by tucsonjwt

Before dropping big $$$ in this truck, I would take it to a mechanic with a modern shop equipped with modern diagnostic tools. Spend $70-$100 on testing and avoid a lot of wasted dollars. You can do the actual repair yourself, just get a good diagnosis first. My $.02. My guess is you only need something minor.
-

Most 'modern shops' avoid older EFI systems like a plague! Unless it is OBD-II most will not touch it. These older systems are primitive by today's standards, but most individual components can be checked with a DVM. If you have FSM basic checks can be done quickly and easily reducing guess work.

//RF

[WuchaGot]

Originally Posted by tucsonjwt

Before dropping big $$$ in this truck, I would take it to a mechanic with a modern shop equipped with modern diagnostic tools. Spend $70-$100 on testing and avoid a lot of wasted dollars. You can do the actual repair yourself, just get a good diagnosis first. My $.02. My guess is you only need something minor.
-

Good advice, Thank you. Unfortunately I have already dropped the bucks, fortunately it wasn't big bucks.

Cap, rotor, plugs, plug wires, rebuilt TBI with new idle air and injectors, thermostat, coolant temp sensor, ignition module, fuel filter, new battery, and the new coil is in the mail.

It all came out to about $450-$500 so not a huge investment and $120-$150 of that was just for fluids for oil and tranny service. And really with the truck parked for so many years a full service was much needed. So everything accept the TBI rebuild I would have done anyways.

Originally Posted by rfmaster

Most 'modern shops' avoid older EFI systems like a plague! Unless it is OBD-II most will not touch it. These older systems are primitive by today's standards, but most individual components can be checked with a DVM. If you have FSM basic checks can be done quickly and easily reducing guess work.

//RF

Older vehicles:

Con: Not many service available.

Pro: Not many services needed! Parts are one size fit all, Simple and cheap. And working on older vehicles is so easy a caveman can do it.

[WuchaGot]

Originally Posted by tucsonjwt

Before dropping big $$$ in this truck, I would take it to a mechanic with a modern shop equipped with modern diagnostic tools. Spend $70-$100 on testing and avoid a lot of wasted dollars. You can do the actual repair yourself, just get a good diagnosis first. My $.02. My guess is you only need something minor.
-

I forgot to mention, parts stores such as AutoZone, and I am sure others offer it as well, loan out OBD scanners to use in the parking lot. I know its not the same as having a knowledgeable mechanic deciphering the scanner codes and using his/her own knowledge of vehicle in conjunction with the scanners reading to pin point issues BUT if you car savy its free.

[rfmaster]

Originally Posted by WuchaGot

I forgot to mention, parts stores such as AutoZone, and I am sure others offer it as well, loan out OBD scanners to use in the parking lot. I know its not the same as having a knowledgeable mechanic deciphering the scanner codes and using his/her own knowledge of vehicle in conjunction with the scanners reading to pin point issues BUT if you car savy its free.

You do NOT need scanner (OBD-I) to read set codes on 87 truck. Just jumper pins A&B in ALDL connector and read SES (or CEL) light flashes. Once jumpered, ignition on, engine off SES will flash code 12 3 times, followed by other codes (sets of 3), if any, that ECM has detected and set in its memory.

//RF

[WuchaGot]

In my first post about this I said that I rebuilt the TBI and one of the vacuum ports on the front of the throttle body was plugged solid.

After I rebuilt the throttle body and re installed it I never put the vacuum line back on because the line was also plugged solid and I wanted to replace it.

Well, I got a wild hair up my ass and crammed the straw from my carb cleaner can into the vacuum line and went to to town. The carb cleaner didn't clear it so I got my professional cleaning tool ( an unfolded paperclip ) and jammed it into one side of the vacuum line then the other and I met a ton of resistance. after I poked and prodded for a few min I stuck the carb cleaner straw back in and shot a few squirts in and a string of rubber silicone (maybe gasket silicone or something, orangish red colored) about 2 inches long and shaped like the inside of the vacuum line shot out one end. Why the heck gasket silicone was in there I do not know.

Anyways, I rushed out about 20 min ago (10:30pm) in 30 below weather and plugged the line between the bottom left vacuum port on the TBI and the connection that it ran to on a black plastic cylinder with a sensor plug on it that also has the 3/4 inch hose running out of it into the side of the air filter housing.

I jumped in the cab and cranked the ignition over and it roared to life with half a turn.

I am starting to wonder if I am attributing successful starts to what I am doing and it is just random coincidences. Does anyone know what I am talking about with the black plastic cylinder that the vacuum line connects to? What is it called and would it attribute to hard starting?

Well, finally, after I let the truck run for a bit I turned it off and the switch felt very stiff and as I turned it of I heard a strange click/snap coming from the steering column as I turned the key to the off position. Out of curiosity I tried to crank it over again and wouldn't start.

First off, cold weather has always seemed to play a role in the hard starts and the fact that is started with half a turn in 30 below weather in the middle of the night gives me hope that the vacuum issue was a contributing cause of my issue if not my issue. BUT now I am also thinking that maybe my issue could be a failing ignition switch that is intermittently connecting.

sigh.

[rfmaster]

@WutchaGot

Hmmm - Which port was clogged? Black cylinder - that could be EGR solenoid, but if you could take a photo of it that would make IDing it easier.



The TB to intake manifold gasket is usually paper, but I have see people use RTV to 'fix' a very common front side vacuum leak where TB bore diameter gets close to outside perimeter flange. Sorry, do not have a photo handy right now.

//RF

[WuchaGot]

Hunted down a few diagrams and if I am not mistaken the "plastic cylinder" I was referring to is the Air Injection Control Valve which has a vacuum line running to the "J" port on the front of the TBI . I have also seen it referred to as the IAS or Idle Air Control valve. Is this the same thing or am I getting two different things confused? I have seen conflicting statements stating that the valve works better in cold weather and fails more when its warm and then others stating that a vacuum leak to this valve will make it a chore to start your vehicle and cold weather makes it harder.

insights?

Thanks again for everyones feedback. Its been a lot of help.

[WuchaGot]

Originally Posted by rfmaster

@WutchaGot

Hmmm - Which port was clogged? Black cylinder - that could be EGR solenoid, but if you could take a photo of it that would make IDing it easier.



The TB to intake manifold gasket is usually paper, but I have see people use RTV to 'fix' a very common front side vacuum leak where TB bore diameter gets close to outside perimeter flange. Sorry, do not have a photo handy right now.

//RF

I planned on uploading a photo but 10:30 at night the photo would not have come out well =) sorry, I will upload one tomorrow .

As for your photo its the "Vacuum port for EGR and EDV" that was plugged.

[WuchaGot]

Originally Posted by rfmaster

@WutchaGot

Hmmm - Which port was clogged? Black cylinder - that could be EGR solenoid, but if you could take a photo of it that would make IDing it easier.


The TB to intake manifold gasket is usually paper, but I have see people use RTV to 'fix' a very common front side vacuum leak where TB bore diameter gets close to outside perimeter flange. Sorry, do not have a photo handy right now.

//RF

I found this photo which is similar to what I have. Actual photo tomorrow.

[rfmaster]

Further to my earlier post - PVC port and TB flange underside:



//RF

[WuchaGot]

When I last left off I had replaced the cap, rotor, plugs, wires, coolant temperature sensor, idle air, rebuilt the TBI throttle body including new fuel pressure regulator, new injectors, new fuel filter, new battery, and new air filter.

After all that she was still hit and miss with starting and even when I did get her started it took a lot of cranking over and it was a struggle.

During the TBI rebuild I found the "J" vacuum port completely blocked as well as the vacuum line. After the rebuild I did not have a new vacuum line so it was disconnected for a few days.

When I installed the new vacuum line and tried starting her she fired right up without a struggle but died when I put her into drive and I couldn't start her again.

the update: I ordered a new ignition/distributor module and a new coil which I received and installed a few days ago. Its been three or four days since replacing the module and coil and she starts on half a crank to 2 cranks and idles smooth right away. She still bogs down if I put her into drive before she warms up but if I let her warm up for 5-10 min first and I can jump in and drive off with out any bogging. ALSO, its 20 degrees and snowing so its even COLDER than when I first started experiencing the problems.

SHE LIVES!

Thanks EVERYONE for all your advice and help.