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Engine stalls for 1 second when decelerating in overdrive.

rumblebee

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rumblebee Enthusiast

rumblebee

Posted
Posted

I'm a newbee here, and really need your thoughts on a strange problem.

 

I have a '99 Suburban LS 4x4. The 5.7 was rebuilt 6 months ago by a shop that was highly recommended, but I've had nothing but trouble since. I won't get into all the problems I've had, but I need help with this one: from day 1 after the rebuild, at 45 mph and above in OD, if you let off the gas there's a brief clunk (the tranny doesn't slip). This only happens after the engine is warms up (runs fine cold).

 

I took it to a mechanic that I trust completely, and he drove it with his scanner connected - when it clunks the engine is actually shutting off for a second (or less), then comes back on. You can't see this on the tach, but he's seeing it on the scanner. In the parking lot, he power-braked it up to 1500 rpm, then let off the gas and it immediately stalled. No codes are showing. The truck always ran great & shifted smoothly before the rebuild.

 

The motor was bored .030 over, flat-top pistons 10:1, and a mild roller cam installed.

 

Since the rebuild I put in a new distributor, cleaned the throttle body, and replaced the TPS & IAC valve. The plugs & wires are a year old.

 

I'm sure that my new mechanic will find the problem, but if anyone has ever had this problem or has any ideas I'd really appreciate you input.

 

 

 

 

rumblebee Enthusiast

rumblebee

Posted
  • Author
Posted

did you reprogram for your upgrades?

 

No - still the stock programming. According to Comp Cams, the cam doesn't require re-programming, but do you think that the higher compression in combination with the cam would mess with the computer?

 

Thanks, and Merry Christmas!

Squirrely Enthusiast

Squirrely

Posted
Posted

Yes I do. You've changed lift, duration, etc. The engine is not programmed to run that cam... no matter what any cam company says. You might need more fuel pressure too. Maybe..

Squirrely Enthusiast

Squirrely

Posted
Posted

Even changing tire diameter can sometimes cause issues with programming. I've seen it on a F250 before. Ran like junk and poor shifting.

rumblebee Enthusiast

rumblebee

Posted
  • Author
Posted

Thanks guys. I guess I'll have to have it reprogrammed. I put 18" Z71 rims with Goodyear P265/65Rs on it too - so I unknowingly threw another wrench into the equation... I've never dealt with mods on a computerized engine before, so this is all new to me. I'm also electronically challenged; my 3 year-old granddaughter can do more with my "smart" phone than I can. Life and Chevy engines were much simpler in the 60's & 70's!!

 

So how do I go about getting it reprogrammed, and who can do this with the modifications?

 

Thanks for your help.

rumblebee Enthusiast

rumblebee

Posted
  • Author
Posted

Update: The mechanic found the problem; the spider injector tubes were in the wrong holes... All of them! I'm glad I found a great mechanic - how many people would even check that on a fresh rebuild?

 

The truck runs good now and the OD clunk is gone.

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      Interesting question which you partly answered in the word 'potentially'. I think that is going to be a 'point of reference' inquiry. What are the touchstones?    This will sound petty but it is the main source of end fighting in threads on this topic. Define a motors "Life". Think about the various arguments that have been entertained on these pages in that very argument.    I can only speak from my viewpoint. Engine "Life" in my world is defined by power cylinder integrity. For the majority of engines it is the bore/ring interface that quits first. Loss of seal. Oil consumption and loss of power. Most Pro motor builders would agree and there is a good deal of information on using "Leak Down" as a primary indicator of bore integrity. At home a compression test is more the thing. If we can agree on that then I think CC Jensen has done its homework and I'd find it valid.    Now by my own definition, Dizzy, wife's Ecotec 2.4 I-4 has been dead since about 80K miles. And yet we have logged over 200K miles more on it. "Life" and "Usefulness" are therefore independent.      I know a mature fella right now who has just hit 300K on a Mitsubishi 3A92 NA MPFI motor and has done compression test every 100K. It was 205 psi after break in and is now about 195 and still even. He uses shelf oil but good filters and adheres to a 3K mile OCI. He even do UOA's on each of them for the first 50K.      I also know a fleet mechanic with that same motor that gets 300 to 500 K out of them but the are oil using, wristpin sloppy, skirt slapping motors. He ran one with a piston pin so loose the piston was bouncing off the cylinder head for about 20K miles before he called TOD. Both of them claim success.         

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