Drivability Symptoms:
My 93 L67, has been severely losing power intermittently. It started a few months ago occurring once a week. Now its up to 4 days a week.

When it acts up, it feels like it is going into limp mode. It takes a very long time to get to 60 mph and sometimes I can barely go more than 25 mph
It doesn’t do any better if I downshift. If I floor it in neutral it howls and will not go over a certain rpm (1500~3000 rpm depending on its mood)
On its better days it has good power except it stumbles and bucks a little at WOT (this may be a separate unrelated problem)

Observations:
It does not throw any codes.
Tranny seems to be shifting OK. Always runs smooth like all cylinders are firing.
Does not make a difference if its hot or cold or raining – occurrence is pretty random. Sometimes it will do this on first start in the morning in open loop and power decreases as it gets warmer.


Work done so far:
Swapped PCM, ICM, and coils with known good ones and it made no difference. (did not have a mem-cal to swap though)
New O2 sensor, TPS checked and adjusted, EGR cleaned and solenoids checked. Plugs and wires have about 8~10k miles.
Last fall it got new fuel pump, filter, FPR, and newer injectors from another member. MAF sort of cleaned (best I could do without removing it)
I have been running without a Cat lately. (my exhaust is flanged so its very easy to swap over to a test pipe.) When I run with the cat, it still has same symptoms on its bad days.

Speculations:
By its randomness and having some good days, I think its most likely electrical.

Dont know what item to tackle next. Any suggestions?

Scan Tool:
Recently got CP9110. This afternoon I was able to get it to run ran bad in a repeatable way:
With car in park, at operating temperature and closed loop:
Case A) When you stab at gas pedal and floor it, the engine will howl, sputter and will not go over 1500 ~ 2000 rpm.
Case B) When you press the gas pedal slowly, engine will rev up smooth and normal and will go to 3~4000+ rpm.



This evening I tried to make it do it again. Initially it would run fine when you stab at the gas pedal. Then it dropped to open loop for a few minutes and still ran OK. When it went back into closed loop it would bog down like what happened earlier in the day.

I don't know if it'* the cause, but 150 LT is the max the PCM can adapt to. You may be pretty lean. Can you get your fuel pressure checked?

Fuel Pressure:
Engine idling with vacuum hose on FPR = 41 psi
Engine idling without vacuum hose on FPR = 44 psi
Engine off with power applied to fuel pump test lead = 44~46 psi
Left gage on after shutting off engine and pressure rose a couple pounds when I checked it 1/2 hr later.

How about PCV and vaccum leaks? Have you checked for those. You are obviously running quite lean and it looks like you have nearly no timing when you get on it.

This would be in line with knock retard seeing something and pulling your timing. The fuel is lean...which points us toward that..also the PCM is trying to compensate as much fuel as possible. Any cracks in your exhaust manifolds that you are aware of? Have you sprayed around the engine with TB or carb cleaner?

Last fall I changed PCV, sprayed around manifold and checked for vacuum leaks. All was fine. Have not checked recently. No cracks in exhaust manifold either.

The part that has me baffled is that I can be driving fine one minute and then out of the blue for no reason, it gets no power.

I think some of the fuel issues might be from running with no cat.

The above data was with the car in park. What would make the engine rev fine when you mash the gas slow but bog down if you press it quickly?

This morning it was weak. From cold start it was sluggish and stayed sluggish in closed loop also. When I got off the highway and pulled away from the stoplight it would barely go. Scanner showed it was in open loop. After a minute or so it went back into closed loop. What could cause it to drop it to open loop without throwing any codes?

Hi roadrunner:

Ignoring the data, and just reading over all the symptoms, it sounds exactly like a plugged fuel filter(except for the irritating intermittent part). I know you put in a new fuel pump and filter not long ago, but could there be some debris in the tank or filter floating around? Then getting sucked into the pump or filter when you hit the gas hard?

Usually fuel filters go more consistently dead, but maybe it'* mostly gone and then the debris gets to it when you demand a lot of fuel. Mr. Wikoff'* first thought was fuel supply, also.

Thanks for the reply Slug. At this point I am not absolutely ruling out anything.

Updates:
I noticed very high mass flow readings ranging from 1500 to 16000 gr/sec (consistently high whether car is running well or not)
There is no trouble code for High MAF (only Low).

I did the full Willwren throttle body cleaning in tech info.
I temporarily put a used L27 MAF sensor in that I got from junk yard (no new 92/93 L67 MAF sensors in stock at local parts stores)
Neither of the above made a noticeable change in the way it runs or MAF readings.

Has anyone seen this problem with a MAF sensor?

I also noticed the CP9110 display for PNP shows “Park/Neutral” when the car is in drive and “Rev/Drive” when it is in park or neutral. The display for PRNDL is correct.
Is this another bug like the issue with the Quad driver showing bad when brake is applied?

I am wondering if I have a bad MEM-CAL and its not calculating proper gr/sec from MAF output. Has anyone seen MEM-CAL go bad without throwing a code?