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Vortec: About to start pulling hair....

TerryD

TerryD

Mildly demented...
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Ok, I installed a new 5.7L engine in our 1999 K1500 Suburban. While there, I did the Delphi MPFI conversion and replaced the MAP sensor because it was damaged removing it from the intake to clean it.

I now have a miss. Several misses, random phantom misses. The only time I've been able to repeatedly recreate them is upshifting from 2-3 at about 1800 RPM. However, that creates misses thoughout the engine when the miss at cruising speed is limited to 1 and 4, with 2 thrown in randomly for good measure. It doesn't miss at high engine load, during hard acceleration, or during deceleration. Only at crusing speed when the throttle is letting off after a small hill or something like that.

I have replaced the spark plug wires, the distributor cap and rotor button, and moved spark plugs around every-which-way and it's still 1 & 4 causing the majority of the problem.

Today I was testing again, and noticed I have also lost my 2nd gear lock in the transmission. In the 2nd gear position, a 4L60E is supposed to be locked in 2nd gear, but I'm getting a 1-2 shift from a standing start and even able to cause a 2-1 shift without abusing the engine.

It also has a hesitation when pulling off from a stop, kinda like a lack of pump shot in a carbureted vehicle.

There are NO modifications to this engine that I'm aware of. I bought it as a stock replacement engine. I'm beginning to suspect that my ECM might have gone rotten while waiting for the new engine, but I don't know why that would have happened. It would not surprise me though, what with the luck I'm currently having with this thing. After putting about $3500 into this project, I hate to just trade it off. I wanted to see a half million miles on this thing but I'm beginning to feel like I should have just sold it off for parts after the engine went out.....
 
Is the cap and rotor a AC/Delco, Delphi or Denso factory part! These are very finicky part and should always be a factory part.
 
It's a NAPA premium one now, it was an AC Delco cheap cap from Advance that had given us about 40k miles without an issue. No difference between how the engine ran with either.

Spoke with a GM Tech buddy of mine last night and he said to swap out the MAF between my truck and the suburban and see if that makes a difference. With the transmission acting up now too, he said that's where he'd start. Gonna try it here after coffee kicks in.
 
Unplugged MAF and test drove it. No missfire. Swapped my MAF from the crew cab in it and started missing again. Unplugged it and the miss went away again.
 
Bet you have a broken wire in the MAF harness most likely right at the connector...


had a similar problem with my brake switch a few years back
 
eagle mark said:
So what do you have? A slew of bad MAF sensors!
Click to expand...

I'm not above that conclusion, but need to drive the crew cab and check the Suburban's harness.
Having two 14y/o vehicles to swap parts on and my luck, I would not be surprised.




62 fat guy said:
Bet you have a broken wire in the MAF harness most likely right at the connector...


had a similar problem with my brake switch a few years back
Click to expand...

Yeah, that's my next step. Having swapped the engine I wouldn't be surprised if a weak wire hasn't broken.
 
Drove the truck to work today with the Suburban's MAF on it. No issues what so ever with the truck. I'm going to test the harness this evening and possibly swap over the MAP and TPS from the truck to see if either of those have any affect. I'll probably borrow an o-scope from work and try to probe the MAF wire at the ecm to see if something looks outta wack with that.

Any other suggestions? The truck and Suburban have the same ECM but the truck has the 4L80E so I can't swap those and expect to drive it.... May try to find a used one cheap and local just to try.
 
You are saying the different MAF solved all problems?

What happens if you put the "bad" MAF on the other truck?

I had a flakey MAF connection at the ECM that drove me nuts for awhile trying to find. TPI, but potential is there no matter what setup.
 
Check your distributor offset, if it's more than 4 or 5 degrees it will cause exactly what you're describing. Adjust the distributor to get it as close to zero as possible and that should fix your problem. Unplugging the MAF puts the ECM in a different mode that covers up the base problem. I had one that I fought for a couple of days before I finally figured it out. It would start adding up misfires when cruising between 1,750- 1,900 RPM on cyls 4 and I think it was 1 but may have been 5.
 
dyeager535 said:
You are saying the different MAF solved all problems?

What happens if you put the "bad" MAF on the other truck?

I had a flakey MAF connection at the ECM that drove me nuts for awhile trying to find. TPI, but potential is there no matter what setup.
Click to expand...


Unplugging the MAF solved it, swapping did nothing. The MAF from the Suburban(where the problem is) is in my truck (no issues/test mule).




bigblock72 said:
Check your distributor offset, if it's more than 4 or 5 degrees it will cause exactly what you're describing. Adjust the distributor to get it as close to zero as possible and that should fix your problem. Unplugging the MAF puts the ECM in a different mode that covers up the base problem. I had one that I fought for a couple of days before I finally figured it out. It would start adding up misfires when cruising between 1,750- 1,900 RPM on cyls 4 and I think it was 1 but may have been 5.
Click to expand...

I don't have a way to chevy that parameter. Anyone know how to add that to Torque? Otherwise I guess I'll have to find a garage with a scanner or go to the Chevy dealership.
 
Had the crank relearn done today and while it does idle better and seem more stable, it didn't help with the miss. Still the front four cylinders and mainly on the interstate after a pull when the load drops on the engine.

I guess my next step is pulling the upper intake off and swapping out the injection unit. Any other ideas? :dunno:
 
Was looking at the LTFT and Bank one was -2.7 and Bank two was -4.7. That strike a key with anyone? I'm going to swap EGR valves with the crew cab and after that I guess I'm going to swap out the injection spider.
 
Slapped my ELM on the crew cab driving home yesterday and the LTFTs were moving all over the place as the engine changed load. The Suburban didn't do that last time I had the ELM on it. The LTFTs just sat there statically and didn't change with engine load. :dunno:
 
Drive it to work this morning because insurance was replacing the windshield in the crew cab. It set a P0753 "transmission shift solenoid 1-2 electrical" code when I pulled it in gear. I cleared it this evening after work, started it and it set the code again when I put it in gear. When I got home, I shut it off, cleared the code, and moved it through the gears and pulled back and forward with it, but it didn't set the code.

With the check engine light on, it won't miss so at least there's that, but I'm running out of ideas and patience. I hate to trade it after dumping $3k into this thing but I'm getting frustrated here.

Anyone know where to buy an authentic tech 2 reasonably priced? I've considered one if the knockoff $400 units and chance it, but a known good secondhand original would be better. Thanks guys.
 
y5mgisi said:
Wish i could help too. Possible bad/missed ground from the engine install?
Click to expand...

I was actually hoping to have good enough weather today to recheck all the grounds. I was also going to probe the MAF leads and the shift solenoid wiring if I can find the diagram.

Thanks guys, just feeling kinda bummed out and need to get off my arse and work on it more.
 
Well, rechecked the grounds. Found the one behind the EGR valve loose, and snugged up the one beside the CPS and the one at the back of the block near the coil. No more solenoid codes, but I'm not holding out much hope til the engine cools down again and I do a cold start. Still missing though.

Got it to happen in the driveway. Loaded up the engine in reverse, when easing the throttle down there was a definite hard miss and 1&4 would count it. Only when throttling down though, not full throttle.
 
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I always questioned the "cylinder misfire" errors on engines with one or even two knock sensors and/or O2 sensors. How can the PCM possibly know that X and/or Y cylinder have an issue, when all cylinders exhaust are mixed together for one bank, and the knock sensor reads all 8? I suppose via some math to figure knock signature vs. ignition firing time they could have done it?

I only question how they arrive at those errors, in case they lead you down the wrong path.
 
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