lol good god man u are the guys that make autozone rich and the employees retarded.
Do you have a scan tool? Or ALDL cable that you can plug into a laptop. Im pretty sure it logs what it's setting the timing to when you plug the EST back in. It could be that the computer is not doing that properly.

 

 

Is your dad's also a 92 Z28 L98?

 

 

Sounds like you have done all the ignition but how is fuel pressure. It could be a injector issue too.

 

 

As long as we're throwing parts at it and since your father has a similar make/model/year and assuming his car runs well, have you tried swapping the EST modules to see what happens?

 

The esc ? Knock filter is part of the memcal.
90-92 l98 automatic would be broadcast code anjf or aujp.

 

You need to hook up a scanner to it and see what the computer is reading.
3500 when cold? Or warmed up. 3500 when car is moving or while in park 0mph?

 

Like pro suggested a scanner might be a useful tool.
I’m wondering if your knock sensor might be faulty pulling timing due to false knock.

 

He said he replaced all sensors lol

 

I was waiting for someone to bring that up.

 

 

 

Has anything been done to the timing chain? I've had carbed V-8s with mechanical advance distributors exhibit the same symptoms when the valve timing was way off after someone switched to one of those "wonderful" double-row roller chain sets using RC35-2 chain barely suitable for a bicycle.

This one started popping in the intake at about 3,800 RPM:

 

 

If you have a dial indicator, piston stop, and timing wheel the valve timing can be checked without disassembling the front end of the engine.

A quick/dirty way to check the timing chain slack would be to remove the distributor cap, precisely mark the position of the rotor, then move the crank backward and forward until there is motion. Note the number of degrees of crank rotation needed to move the distributor rotor, then multiply that by two to determine the timing chain lag. 30° of valve timing lag is a LOT.

Incidentally, shall we close/merge your thread in the TPI section to reduce the confusion?

 

Holy sheep stuff Vader!!! Somebody put that one together with the cam ADVANCED 2 teeth! I'm surprised it ever ran at all, especially without crashing the intake valves into the pistons.

And of course, the crappy "roller" chain with all the slop, that isn't roller at all, just tops off the whole "improvement" session...

OP, you need to see what the FP is WHILE IT'S IN THE ACT OF SCREWING UP. Not, sitting in the driveway idling; not even, holding the throttle up to whatever RPM. Needs to be checked by your assistant while you are driving it down the road with the FP gauge taped to the windshield. (or vice-versa)

 

Yup. 35½°. Idled just great with an Imperial long-ton of vacuum, too. It either jumped on shut-down (not a first) or someone installed it that way. I had to believe the former, since it ran just fine for several years with that chain before falling int my lap. Not a fan of bicycle chains...

Occam nearly decapitated himself on that one. I had to stitch him back up.

 

Out of curiosity, how did it come to infest your lair?

 

 

When you disconnect the EST, you disable the ability of the ECU to adjust timing.

You are running on straight (usually 8-10-degree advance) mechanical timing with the EST disconnected.

Something is happening at 3500 RPM that is sending bad information to the ECU.
The bad information sent to the ECU is causing it to incorrectly adjust the injector pulse.

Until you get a clear read on the fuel trims at the time this happens, you can parts-cannon until you are blue in the face.

 

If it is a sensor sending bad information, you can disconnect one sensor at a time while running a scan-tool that provides live fuel-trim data to see whether the absence of a particular sensor makes the problem go away.

If disconnecting a sensor sends the problem into remission, you can then diagnose whether its the sensor failing, or failed wiring between the sensor and the ECU, that is at fault.

 

If the problem cannot be traced to a sensor reporting faulty infomation to the ECU, then you have to go through all corners of the intake system to eliminate vacuum leaks as a possible cause. If not vacuum leaks, then test all wiring and devices that deliver spark. If still nothing, then look for mechanical fuel-delivery issues. If nothing there, assess compression.

And really none of these in any particular order except what your experience may lead you to suspect one possible culprit over the other.

As always, an internal combustion motor will only run normally if provided correct air (temperature, volume and density), and correct fuel (quantity and grade), and correct spark (intensity and timing), and compression.

 

No actually, I was asking Vader about his lovely photo up there; I was wondering things like if it was still running at the time, how long it had been experiencing whatever trouble it had (obviously the parts had been running long enough to get sludged up pretty good), and such as that.

In your case though, what's the history of your problem? Bought the car that way? Just appeared out of the blue? Started after some kind of work had been done or something else happened? Started out barely noticeable or only occasionally, and has been steadily getting worse?

And, what's the fuel pressure WHILE IT'S IN THE ACT OF SCREWING UP, driving down the road, with the FP gauge taped to the windshield?

 

I knew the owner pretty well. I had done a couple TPI conversions for him previously and he had exhausted other resources. The engine in the car had been "built" about 2-3 years previous and had been run extensively every summer for several thousand miles, including one Power Tour. It started getting "wonky" right out of the blue one fine summer day. Everyone before me checked everything they could think of, and at some point someone MUST have corrected the ignition timing before it landed in my place. I'd checked all the usual suspects first, including lift on every lobe (at the rockers) before throwing the spacer (deep socket) and timing wheel on the crank. That led me to the inevitable.

Since it was apparently O.K. for two or more years I suspected a jump of timing at shutdown, not completely unexpected given the compression and the bicycle chain. It had a ton of slack, too.

 

Yeah Vader, Occam would not have expected a cam to jump to a more advanced setting, I'm sure. But who knows what evil lurks in the hearts of "bushing roller" aka "truck" chains. Those things are SUCH CRAP... the fact that they sell for less ¢¢ than an already cheeeeep stock one, ought to send a clear enough message; but apparently some folks just don't get it.

 

Merged thread from TPI Forum

 

 

Nope, not the knock sensor. Don't mess with that.

Not the "timing". Don't mess with that either.

The more stuff you mess with that's NOT the problem, the more work you will have to do to put things back where they belong whenever you DO find whatever IS the problem.

Moral of the story: LEAVE STUFF ALONE if it's not broke. Concentrate on finding what's broke, NOT on just MESSING WITH everything else.

Get a fuel pressure reading while driving down the road WITH IT IN THE ACT OF SCREWING UP. Gotta have that before going any further.

If you don't have the right fuel pressure, you can change EVERY SINGLE sensor under your hood EVERY SINGLE DAY, and even TWICE on Sundays just because you've got nothing else to do, and it will STILL screw up THE EXACT SAME WAY.

Leave the sensors alone and CHECK THE FUEL PRESSURE while it's in the act of screwing up.

 

Ok I will check Friday and see what’s up but I do got a new fuel pump filters tank fuel regulator checked the relay so I don’t think it’s fuel but never hurts to check

 

Sofa tells the truth even tho he loves capslock lol.

Tsmith, move the map sensor out of the way but dont disconnect it. Then run the pressure guage and just lay it on the windshield, then put down the hood down to about where it catches the latch but doesnt close all the way. It helps if you have a 90 degree connector so that hose isnt point straight up at the hood all of the time.
And please get a scanner. Even if its a cheap one that runs bluetooth on your phone/tablet:

https://www.ebay.com/itm/12-Pin-ALDL...0AAOSw9mFWHvks

So you can see what the computer is thinking instead of just guessing.

When u get done driving, do this:





https://www.youtube.com/watch?v=4_f5...youtu.be&t=173