any 6.2 gurus out there??

[n8r67]

looking for some 6.2 gurus.....I have an 86 m1008 that I installed a gm5 turbo. I did turn the pump up the 6th turn and am running the 6.5 injectors, intake and ele lift pump. Now, im happy with how it runs dont get me wrong. Its quick to spool to 10psi egts stay under 1000. just recently I noticed though at crusing speed, occasionally under accelleration, it feels almost like a "powerband" and runs really well for short bursts. almost like a shot of nos. would be awesome if it ran that great all the time?? any idea what would cause this? is there an accelerator in the ip pump or something that could be sticking?? truck only has 60k, fuel filter is brand new. lift pump only has maybe 1500mi on it?? dont think Its a fuel supply Issue?? anyone experience anything like this??

[Cabnchassis]

Both my 6.2s will feel like they surge a little right around like 60 in the burb and 65 in the CC. I don't know what causes it but you'll get this kinda weird feel like it punched the throttle itself for a sec or something. Both been doing it the whole time I've owned them. Doesn't cause any problems I'm aware of cause that CC has been doing it the last 5 years although it happens more in the burb. If you weren't paying a lot of attention you probably wouldn't even notice it happen. Not educated enough to say what causes it though. Also not sure if this is the same problem you are getting just amplified cause of the turbo or completely unrelated?

[Cabnchassis]

The real knowledgeable folks should show up soon but today I was thinking about an IP problem I had in a 7.3 IDI and it reminded me of this. You'd be driving along, and it'd lose a ton of HP suddenly. About the time you got sick of that and had the pedal all the way floored, it would surge back to full power. It was actually kind of dangerous at hwy speed cause it could go from 65 down to 50mph then shoot up to 70 faster than you would believe that old box truck could accelerate. That motor was a used replacement and had sat in a wrecking yard for a long time. The mechanic that worked on it just replaced the IP and all was well, but he said most likely that was caused by a flat spot or some other kind of wear on the pump impeller. Idk if he ever took it apart to see exactly but the new IP solved it. Obviously that's way worse that the little goose mine gets but it was a similar feeling sometimes and they are both NA trucks with mechanical injection pumps.

If it was a gasser I could be a lot more helpful but these are my first detroits and the only ones I've ever been around, the only things I've had to fix are wear items

[Corts60]

My Olds has the same DB2 injection pump as your 6.2, just different casting. The only time my pump surges like that is when it is about to run out of fuel or I have a clogged filter. Perhaps try and change your primary and secondary filters (I hope you are running two).

[Cabnchassis]

As far as I know I only have the one on the firewall in both of mine. Any suggestions on what to use or buy as a secondary filter? I change them regularly but I'm aware of how low quality some fuel can be.

[Corts60]

Originally Posted by Cabnchassis

As far as I know I only have the one on the firewall in both of mine. Any suggestions on what to use or buy as a secondary filter? I change them regularly but I'm aware of how low quality some fuel can be.

I run a Racor water separator primary filter and the stock secondary filter. As a general rule of thumb, the primary should be around 10 micron and secondary should be 2-5 micron.

[Cabnchassis]

Originally Posted by Corts60

I run a Racor water separator primary filter and the stock secondary filter. As a general rule of thumb, the primary should be around 10 micron and secondary should be 2-5 micron.

Thanks I'll start looking into it.

I know you 5.7 guys really like those things. This one has been on CL in my area for coming up on ten years now. Could probably had for next to nothing if you know anyone looking. I'm so sick of seeing it on there I'd love to find it a home

http://sfbay.craigslist.org/pen/cto/4718033142.html

[thirdstreettito]

It's either vacuum or fuel. Grab a vacuum diagram and check all the lines, make sure they are all routed correctly and not dry rotted. Second, make sure you have a new fuel filter(whether stock or screw on). If there is no problem there then you may have some old rubber fuel lines disintegrating into mush or air in the system somewhere. Also, check the high idle switch, if it's bad it can turn on intermittently causing a surging feeling.

[n8r67]

Originally Posted by thirdstreettito

It's either vacuum or fuel. Grab a vacuum diagram and check all the lines, make sure they are all routed correctly and not dry rotted. Second, make sure you have a new fuel filter(whether stock or screw on). If there is no problem there then you may have some old rubber fuel lines disintegrating into mush or air in the system somewhere. Also, check the high idle switch, if it's bad it can turn on intermittently causing a surging feeling.

well nothing (I know of) is vacuum other than trans. the waste gate I converted to mechanical (spring). the fuel filter is stock but brand new. high idle works great when cold starting? "ugly" fuel lines have been replaces but cant out rule that one?? air in system I dont know how to investigate that??

[thirdstreettito]

Originally Posted by n8r67

well nothing (I know of) is vacuum other than trans. the waste gate I converted to mechanical (spring). the fuel filter is stock but brand new. high idle works great when cold starting? "ugly" fuel lines have been replaces but cant out rule that one?? air in system I dont know how to investigate that??

The high idle(cold start advance module)I thought was vac operated, but it's been a while so I'm a bit rusty. Anyway, you said it is an M1008, which means it sat for a while, diesels can grow algae in the tank and the it comes loose after using the truck and can clog the pick-up in the tank and the filter. The easiest way to check for air in the lines is to install a clear fuel line and run the truck, if you see anything other than constant fuel, then you've got air. After that you'll have to check every little part of the system. And yes, you'll want to kill yourself before, during, and after. lol

[Cheng]

I was beginning to have hard starts and some surging on my 6.2 last year after changing the fuel filter. After much troubleshooting i found that the filter restriction indicator o-ring was beginning to leak. I disassembled the filter housing completely and was able to replace all the o-rings including the heater element and vent/drain screws from a local hydraulic supply house. Starts better and runs smoother ever since. Also when i pulled out the heater element it was pretty well clogged with 28 years of debris.

[Cabnchassis]

As if my truck knew we'd had this conversation, it came home on a wrecker friday. I noticed a little shaking sitting at a light which was odd cause my truck doesn't shake ever. Then when i pulled into a parking lot and let off the fuel the truck died. I was afraid of an air bubble so I immediately got it started and got on the highway to get it closer to home (Its $125/hr to tow a dually around here). It surged like it had some air bubbles or something for a sec when it started, or kind of like those big old detroits they use on generators trying to hunt for idle. The power was off on the low end for sure and I noticed that it would run fine as long as I had my foot in it, but when i got off the highway to get diesel before i took it home, it died as soon as I let the rpms fall to idle and wouldn't restart. Acted like there was no fuel hitting the cylinders. Now that it's home I changed the fuel filter and went to bleed it but I'm not getting any fuel a the injectors. The only thing I did different was where I got this tank of diesel and how low I let it run. The truck did not run out of fuel unless it's pulling air after the filter.

Any ideas where to start on this one? I have a hard time thinking it's the IP itself because even running bad at an idle when I put the pedal down it ran totally normal. The other reason I would lean toward bad fuel or a spontaneous air leak is that the truck had no lead in symptoms other than putting fuel at a station I've never used, nothing at all was different and this has me kind of confused.

[hatzie]

Mechanical lift pump failure, air leak in the fuel lines, or the leaky POS Stanadyne 80 filter housing. The DB2 & DS4 injection pumps will pull enough fuel to run with a dead lift pump as long as you don't develop any air leaks but a split lift pump diaphragm can pass fuel into the crankcase.
My 2000 and 1976 have electric lift pumps and the M1008 has the original style mechanical.

The 6.2L bible is in the scanned tech school textbooks in the RTFM....

[Cabnchassis]

Sweet, thanks. I'll start at the lift pump. The filter housing could have some air leaks too, I'm definitely not a huge fan of that system and once I get the thing turned back on a secondary fuel filter is on the short list.

[Cabnchassis]

It ran too clean for air leaks before it died so I just went after the lift pump first since it was less than $25 and was leaking oil around it anyway. A little battery charging, a little swearing, and some line wrenching and shes good as new. Thanks for being dead on with your advice. Makes life a lot easier.

PS if you haven't done one (I hadn't) it's a diaphragm pump and if anyone does this and can't get the fuel pump to bolt back in easily you probably didnt push the rod that drives the diaphragm far enough back into its housing... At least I only wasted an hour trying to understand why it wouldn't line up with the bolt holes before it dawned on me how that system drives the diaphragm and that the drive rod was obstructing the diaphragm lever.