So heres the problem, Basicly the engine does not like to rev past ~3500 RPM under load. The engine will backfire through the intake, run flat with very little power and all around run poorly. To test I put the car in 2nd gear and brought my speed to get it to around 3500rpms. I then tried to accelerate via full throttle, 50% and 25%. Both full and 50% throttle produced same results ie stumbling, backfire through intake and lack of power. At 25% throttle the symptoms where there just less pronounced.


Ok, things Ive done so far:

Replaced fuel pump/filter & installed adj. regulator. Ive verified 42lbs fuel pressure at the tap. Ive also verified fuel pressure is ok while under load as well.

New Plugs/cap/rotor

New distributor coil and HEI module

Verified voltages on TPS

Verifed IAC working

Checked timing with computer disconnected, its good.

Ran a bottle of chevron techron fuel injector cleaner through it.

Verifed no trouble codes.

Verified cpu goes in to closed loop as normal.

Verified no exaust problems

Verified no vacuum leaks

Adjusted valve lash (engine running, back off till clacks then 3/4 turn in)

Visually inspected valve train, everything looked ok (no broken springs etc)

Checked Timing chain slack, it was about 4-5 degrees

Ive had this problem for ever and cant seem to figure out whats going on, its driving me crazy! Ive searched through the past posts here and a lot of people seemed to have a flat cam lob, but while adjusting the valve lash, I didnt notice anything wrong ie the rockers were all going up and down normally.

Anyone have any tips or suggestions?

Thanks all!

 

Welcome to thirdgen.org.

What year is your setup? MAF or SD? If MAF, diconnect it and try.

Have you checked out the PickUp coil?

Checked for exhaust restriction?

Since it's an L98, should still have the rollercam, doubt a lobe is flat.

Timing chain slack *should* cause a lowend loss due to retarded cam timing, and actually run better in the high RPM's...but it is excessive slack, but don't think it's causing your problem.

 

Its SD

How do you mean pickup coil? Ive replaced the coil in the distributor.

Ive gone up and down the exaust and its ok. Ive removed the cats just in case, same problem.

I really really want to just go and shoot this thing.

 

The PUcoil is located around the distributor shaft, underneath the reluctor...8-pointed thing..has two wire coming from it that plug into the module under the cap.

Resistance reading should be at 800 ohms +/-20, and stay steady while wiggling the wires. Should also be no greenish crud on it.

The part is cheap (about 10 bucks) but requires you to pull the distributor, take off the drive gear, and slide the shaft out to replace.

Notsure if it's your problem of not...if it was not working, it'd do as you describe, but should eb accompainied by the SES light going off at the same time, indicating the ECM is not receiving ignition pulses.

Did you scan for codes, BTW?

Also, did you put the grease under the new module when you installed it?

I dunno, just seems to me like your problem is more ignition related, than fuel.

 

Another thing, since you're SD, is you can test the MAP sensor....Been awhile, but you have to have the key on, and use a MighyVac or similar...with no vacuum, IIRC, you should have 5v out, as you increase vacuum, voltage should drop close to zero..hope I remember that right, and don't have it backwards...anyways, the MAP should hold the vacuum pretty much indefinitely as well...i/e apply 20in/hg and let it sit...should not drop off for quite sometime.

 

Its not throwing any trouble codes that would make it too easy

I'll check voltage on MAP sensor tomorrow.

 

MAP Sensor seems ok voltage wise.

 

OHM out the PUCoil. Look for the greenish crud I mentioned before.

Did you even get the code 12 to come up?

 

I had the same problem with mine for the last month and no one could figure it out. Come to find out it was the prom loose the first time it acted up about 3 months ago. The second time it started acting up it was the whole ECM. I replaced and havnt had any problems since. I PM'd you but you never wrote back for the info.