Still chasing poor running

[FormulaReed]

First off, many thanks to all who have helped me out so far. I?ve been chasing this same issue for 2 years or so, so I?ve got to be close right?

Here?s what it does: I will be driving along, car feels great and then it feels like the throttle just lifts off, revs go down, but mostly power just falls way off. Some times it snaps out of it, and will have all its power back, other times it just keeps running poor. Most of the time it will idle, but not want to rev. Other times it will completely die.

It?s only ever tossed a code one time, for a cam position sensor. One time, I was able to catch it die on my scanner. It went from showing normal data, to zeros.

I?ve had this same issue for years now. When it runs right, it?s really good. Sometimes it will run all day great, other times it will not make it around the block.

My car had headers & exhaust, but no other mods. The only known issue is my tach reads high.

I don?t think that I have any vacuum leaks. My pump primes and shuts off. It will hold pressure for hours.

Things I?ve done in the past 2 years:
Fuel pump (replaced stock pumps, finally did single pump conversion)
Fuel filter and lines
Map sensor & vacuum hose
TPS
Crank position sensor
Cam position sensor
Sent ecm to Halbeck: tested fine. Got new chip programmed
Battery
Alternator

Previous owner (in last 4 years)
Injectors
Coil packs
Plugs (pulled and look good)

If anyone has an idea, let me know. Kinda running out of ideas?. The only thing I can think of is the chip adapter has gone bad. I don?t think I?ve got the stock chip, but if I do, should I try swapping it in?

Thanks,

Reed

[viper107]

i would try a differeant ecm

[A26B]

It sounds like an intermittent harness connection. It is not a common issue but has happened before. Probing the ECM harness connections can enlarge the female side of the connector resulting in an intermittent connection.

[Vette Guy]

I agree with both assessments. I had a similar problem, but with an 91 L98. I'd drive for sometimes 20 minutes without issue, then all of a sudden there was a loss of power and it would not rev. I'd be scared I wouldn't make it home. No codes. As it was my only transportation for a while, I had to drive it over an hour away to visit relatives, and sure enough it happened along the way. I moped to my destination, then was telling my car story to family, and showing then the car running poorly. I happened to put my hand on the ECM and it was hot. With not much to lose, I tapped it, and whala! The car immediately began running fine. I made it home, having to stop along the way for another tap or two, but after months of hunting the issue, I finally isolated it to the ECM. I replaced the ECM and never had another issue.

Good luck!

Regards,
Mark

[tccrab]

Originally Posted by A26B

It sounds like an intermittent harness connection. It is not a common issue but has happened before. Probing the ECM harness connections can enlarge the female side of the connector resulting in an intermittent connection.

Yup.
That was me.
I had bad injectors, tested them by pulling off the big connector on the ECM and probing the sockets with my DVM.
I did confirm injector failure, but also managed to physically stretch the female connections in the process.
There was no obvious way to tell i had fubared the connection, it was just that the male pins were sloppy loose in the female connectors
The car would start and run fine, but after it would warm up, i'd get an intermittent misfire and power loss.
You wouldn't believe how long and how much $$$ i spent tracking down the problem and then finally fixing it once and for all.
The fix was cheap, i bought the female pins for $20.00 or so, borrowed the correct crimp tools, and re-pinned the harness. Not an easy task, but fairly easy to do with right tools.
Tracking down the fault i replaced: spark plugs (twice), spark plug wires (twice), coil packs, fuel injectors (twice), ECM (they weren't cheap back then too, although available at the local Chevy shop), three sets of plenum gasket sets and two sets of injector o rings, And i don't remember how many sensors i bought and swapped.
Suffice to say, it wasn't cheap, nor did it happen quickly.

Just goes to show you, don't make a problem bigger by underestimating the problems you cause during the diagnosis of the original fault.

Crabs

[WARP TEN]

Originally Posted by tccrab

Yup........I did confirm injector failure, but also managed to physically stretch the female connections in the process.
There was no obvious way to tell i had fubared the connection, it was just that the male pins were sloppy loose in the female connectors
The car would start and run fine, but after it would warm up, i'd get an intermittent misfire and power loss...... Crabs

Sounds like my sex life. Very familiar with the misfire and power loss...Bob

[FormulaReed]

Thanks for the reply?s!

Other than jiggling the wiring harness, or replacing the pins, is there any good way to check or test?

My first step is replacing the chip adapter. I don?t think this is the issue, but before I plunk down money for a new ECM, I figured it was worth a shot.

I got a new one from BoostedNW, and it?s a very nice piece. It?s got a little tray to support the factory chip and everything went back together with satisfying clicks. I?m going to drive it tomorrow and see how she does.

Reed

[wfot]

for what it is worth, you do not need a new one, you can send yours out to be fixed....

I had similar issues and it was a cracked motherboard, hot soak made it do weird things. mostly told me it was the cam sensor... I have 3 cam sensors now....

[FormulaReed]

I did I a bit of digging on this forum and found my car. From what a gather, the ecm is what took it off the road, and it?s been repaired before. I?m thinking that a replacement ecm is in my future.

Anyone got one they will part with? Saw one in the classifieds and sent a message.

Thanks for all the help so far. I will post my results when I get a replacement

[WARP TEN]

You said you sent the ecm to Marc Haibeck and he said it was fine. Any thought of sending the whole car to him for a thorough going over? Marc has a history of discovering problems and solutions for them that few others could come up with. Had our regular lunch with him recently and he recounted a long ago situation of a 415 car that was running rough not putting out the power expected of it. A dismantling of the engine showed that it had not only been severely overheated at one point, warping cylinder liners, but also was not a 415 at all but a much lower displacement engine. Not suggesting you have such a problem, but Marc has had a pretty good track record of solving problems that others can't. We fairly regularly hear such stories from him. Anyway, just a thought, although I know it's a tough decision being a bit far from his Chicago area shop. Still, lots of good advice here from our very experienced forum members. Good luck with it. -Bob