dr bob

That car was first ppi'd by Greg when your PO bought it, so it already knows his loving touch. good luck on this, and keep us informed of what you discover.

Some posts suggest that there's been other work done on the car in the middle of this battle. ie- You mention the coincidence of oxy sensor writing and grounding since you had new belly pans put in. In my limited experience, there are seldom coincidences like this. I recommend that you list the work you have done recently, and add in the appearance of the various symptoms in a chronological fashion. Perhaps that will help us all see possible correlations with you.

safulop

At this point they have checked and rechecked all reference voltages and resistances, grounds etc. so we are down to some pretty bizarre theories of the crime. The real choices are, intermittent problems with LH or MAF, or wiring in between.

Rich Andrade is graciously sending over new MAF and LH, so we can at least eliminate this strange possibility before shipping it down to LA. This idea would mesh with the chronology of symptoms.

Here is the complete recap:

Spring 2015 - Car runs apparently fine. I decided to try Porken's chipset for both EZK and LH with the 24# injectors. The shop did this work, and when it was reassembled, the car was flooding rich. - this marks the first ever appearance of the problem, it seems.

Went through the whole song and dance we are going through now, after first undoing the new chips and going back to old chips. Not having spares, we sent the LH and MAF out for checking and possible repair. Both checked out and were sent back, with stock LH chip. Baffled, the shop reassembled and lo and behold, except for some arcing in the plug wires she ran well with 2 exceptions. First we installed fresh plug wires to correct that arcing.

At this point, the car lost 1 mpg of mileage - indicating rich running, for unknown reason. Also a strange problem developed in the idle control loop, where the car would idle as high as 1800 rpm when first started (depending how cold outside, this would range from 1400-1800), and then slowly settle down to spec 675 rpm when fully warmed up. Still don't know what is/was causing this. I ran it daily in this condition for several months and did no work on the car.

In January I replaced the EZK chip myself with the Porken one. Car ran well after as before, with the noted improvement from the new chip, although still with the high cold idle speed.

Then I had to replace my alternator cooling hose, install belly pans (both), and a new Temp II to try to fix the high cold idle. Car's cold idle was down by about 200 rpm compared to previous and also corrected faster, but still kind of high.

One day after these repairs were completed, the flooded running began, first at wide open throttle (see thread title). After a week or so driving it around like that, it finally went full rich and refused to run.

This progression is consistent with the theory that the MAF was bad in the Spring, then self-corrected during shipping around the country (although not completely), then finally went bad for the last time now.

FredR

Trying to analyse your chronology as written gives the impression that along the way you may have been running 24lb injectors with stock programming- I doubt that happened but perhaps you can eliminate that possibility.

The problem started when you initially changed out the injectors and the chip sets - that is significant suggesting either something is not right with the new components or something was inadvertently damaged during the install. Without going back through the entire thread have you checked out the 24lb injector part number and compared to what it is meant to be?

You use the term "flooding rich" perhaps you can describe what you mean by this terminology- from my perspective running rich is one thing- flooding is another dating back to carburettor days- either way I presume you mean so much fuel was getting in there that the plugs wetted and would not fire as a consequence.

I think we can eliminate the EZ chipset as being a part of the problem. Eliminating the MAF and LH computer elements are the next sensible step but if you use the stock items you will need to have stock injectors installed.

You clearly understand the importance of temp 2. This output sets the LH response to what it perceives to be engine temperature. During warm up the LH recognises the resistance value and enrichens fuelling and increases rpm's until the motor warms up and then the warm up map progressively reduces these factors until it is running normal at working temperature. If something corrupts these signals then a false reading is what it is.

The only other oddball thing I can think of is if the wiring loom has been corrupted [rodents chewing into the loom somewhere?]. I have the impression you have eliminated such possibility. Mechanically damaged/degraded wiring can produce erratic results as things heat up and vibrations shake things around.

Having followed your thread you have my sympathy- apologies I cannot come up with something more meaningful obvious as the above may seem.

Rgds

Fred

safulop

OK the shop is deep into this car now and it seems like we have fixed the main problem... with a new MAF. This was surprising and baffling, because it means that the previous MAF which was rebuilt in 2007 or so not only failed, but suffered intermittent failure. So, it first failed last summer, then bench tested 100% good when removed and shipped across the country, then worked for several months when reinstalled, then failed again.

So they now tell me the mixture control is good, but we need an intake refresh. This also surprised me since the intake was removed and powder-coated in 2008 or so, but it looks as if the flappy valve has been frozen shut for approximately 25 years. So that means I have never actually had full power on this car since I bought it.... a disappointing revelation.

Had to replace ISV since it was completely frozen as well. This must have been causing my idle issues -- yeah. So basically, stuff I thought I knew was good to go on this car (rebuilt MAF, intake stuff) turned out to be so much old junk. At least I do not have to ship the car down to Anaheim.

safulop

I would have recognized the initial problem as an MAF failure if I had thought that was possible, and if I understood more about those symptoms. I have since read about how a failed MAF can cause fuel starvation at full throttle coupled with rich idling. Makes people think they have fuel line/pump issues (see first posts). This is due to the sensor under-reporting airflow at load, but over-reporting at idle.

Live and learn!

safulop

OK folks,

with a final thank-you to all who contributed advice,

I declare this thread SOLVED.

I finally got my car back, after several rounds of "whoops, something else under the friggin' intake is broken, can you call your guy in Texas and send us some parts".

So the forensic analysis shows that, indeed, the previous rebuilt MAF lasted only about 25K miles before it started to die. Problem was, it died, then revived for several months, then died for good. And the first death occurred by coincidence when chips were swapped. So yeah, I hate coincidences, and bad rebuilt parts.

Another weird thing was the discovery that my PO had removed and "refreshed" under the intake, but left a bunch of really bad parts in place -- notably the ISV and the flappy valve. Normally when you buy a 928 and there is evidence of an intake refresh, it might not be your first instinct to remove the intake and check underneath, but hey. . .

You can rest easy on this one for a couple weeks now Roger. Maybe.

At least the shop had so much time on their hands waiting for my parts, they painted my intake for free. I like guys who love cars.

-Sean

dr bob

Glad it's sorted again. Thanks for sharing the odyssey with us.