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After months of work - stretched out by budget, time, and the particular approach I have taken, here's the status of my 86.5. "Particular approach" might need some explaining, as it has been the principal reason this is taking me so much time. When I began this project in January, I decided to attempt to identify the particular reason for the "rough running". It's not the approach a professional mechanic would take, and I know that because at one point in my life I was a professional mechanic, in the sense that I put food on my family's table by turning wrenches, NOT in the sense that I was greatly skilled. A pro would say, "what? over 200K miles? Here's what we'll do", and that means replace everything that would be worn out at this mileage, period. Nothing wrong with that, in fact, it is the fairest approach to take for the customer's sake. But I wanted to identify and understand the root cause of the problems I was having. So:
In my first post I enumerated the steps I had taken by mid-August. Then:
-verified correct plug wire installation approx. 50 times (if you count the number of times I did it in my sleep);
-fixed all vacuum leaks replacing all vac lines with new Porsche or OEM (made a version of the PVC pressurizing fitting to check) and completely removed air pump system (but some day may reinstall it, so saved all the bits);
-replaced the ICV after determining that although it mostly worked, it was sticky (and was not an original 928 part);
-had the MAF rebuilt
-rewired the TPS harness, MrMerlin was right on about the faulty connection at the top of the of the water bridge;
-replaced one of the ignition control units (amplifiers) after determining it was bad (separate thread on that);
-installed new x-pipe, with new O2 sensor (the old cats had broken and completely blocked the exhaust).
All these steps improved idle (drastically) and no-load performance, but under acceleration there is still a pronounced "stuttering" (which is very regular, as opposed to random misfiring) and lack of power.
My attempts to use my o-scope, even with the good counsel of Dr. Bob, did not give me the kinds of traces I thought were reliable, but a new pickup is in the mail which should fix that problem. A quick plug read (one from each bank) looks normal. So now what I am suspecting is poor fuel flow under load, and along with scoping the ignition, I hope to have time this week to measure fuel pressure (at the rail) under load and see where that is. I will also be replacing all fuel injector connectors (thanks for the tip Dr. Bob on the $20 adapters- got a set, the connectors are AMP and the pigtails look to be of good quality) whether they appear to need it or not.
In other words, I'm still plugging along. Each step has resulted in some improvement, but has not solved the problem. In fact, performance under load has gotten worse. (Maybe I should look at that timing ring!?) But it's still fun, or at least intellectually engaging, to try to figure this one out, and I hope to have another report sooner rather than later.
Meanwhile, all comments welcome! They have been very helpful so far.
First of all thanks for bringing this post up to date.
Going out on a limb with this but after re-reading all you've done so far, about the only thing I did in my recent complete upper refresh that you haven't done was to replace my battery grounding strap. When I cut the old one open, I was shocked at how much corrosion there was under the sheathing. And I know how temperamental these cars are about the correct voltage at all times. Could this be as simple as you have an old battery ground strap that needs replacing?
First of all thanks for bringing this post up to date.
Going out on a limb with this but after re-reading all you've done so far, about the only thing I did in my recent complete upper refresh that you haven't done was to replace my battery grounding strap. When I cut the old one open, I was shocked at how much corrosion there was under the sheathing. And I know how temperamental these cars are about the correct voltage at all times. Could this be as simple as you have an old battery ground strap that needs replacing?
It's new, but the old one (replaced a few years ago) was truly toast! Other grounds have been cleaned, forgot to add that to the report.
It's finally back on the road, and running very well, reflecting all the repairs/replacements done during the refresh. And a few more tools, mostly diagnostic eqpt., were added to the inventory - FI pressure gauge kit, 8 channel scope adapter for my laptop, some other stuff. So what were the problems that remained after the work I described? There were two, and they were pretty simple. First, the FI wiring harness side TPS connector, though I had repaired it, was still flaky and intermittently not making connection. And second, and this is a bit embarrassing, bad gas. Shoulda thought of that since it had been sitting since January (even with fuel treatment that was too long). Sure is nice to have her back on the road!
Thanks, Bertrand and Seth. "Plugging away" was the mode, dealing with one thing at a time and trying to learn the "why's" behind the problems. Everything I did made a difference and it was interesting to see the interrelationships of all the variables. Diagnostics-wise, the collapsed cats masked a lot of other problems, and the bad gas kept me from seeing the big improvement the X-pipe made. That is, until it went up and down the lift for restarts and test drives half a dozen times. I had put a couple of gallons of new fuel in the tank for the tests, and when I noticed that the running seemed to improve each time I tested, the light bulb went off about the bad gas. A dim bulb to be sure, but it's done. I'll post a pic of the engine compartment later- does look a lot better, although certainly not as spiffy as either of yours.
Great job Martin!! Great thread. Really appreciate the in-depth descriptions of what you did and what you learned. Engine looks fantastic...and I know the bottom looks just as good.
FYI all....Martin's car is Plasti-Dipped. I can't recall if he did it to preserve the paint...or hide the paint But the gray will peal off.
Great job Martin!! Great thread. Really appreciate the in-depth descriptions of what you did and what you learned. Engine looks fantastic...and I know the bottom looks just as good.
FYI all....Martin's car is Plasti-Dipped. I can't recall if he did it to preserve the paint...or hide the paint But the gray will peal off.
Jon, you crack me up! The purpose was to hide, for sure, and peel for a refinish after all the other work is done. But next comes drive train: torque converter is leaking, TT probably needs attention. etc. Another trip through the wormhole to the dimension of penury...
Hmmm...You must have been the mechanic who read Zen and the Art of Motorcycle Maintenance (Quality!) and A Brief History of Time. If space-time is bent just right you can jump into that worm hole and emerge at a place and time when your torque converter wasn't leaking. Or you could just fix it.
I also have a slow leak that drips from the torque converter housing - but only leaks after shutdown. Shocki posted some video links to great YouTube videos by a Mercedes mechanic who sells repair kits with full instructions (the guy who drinks a lot of orange juice while working). If you don't have these videos, I'll send the links to you. Very useful for diagnosing your leak. The pump seal or the torque converter seal often leak, but the leak behavior is different. If my memory is true, my "leaks only when parked" is the pump seal, and since it's leaking very little, I have chosen to top off the fluid as needed. Seems like about 3-6 months between toppings - but I only drive the car about 3000 miles a year.
Curt's TT bearings were growling at Frenzy...so you two can do a rock, paper, scissors thing to figure out who starts first and creates the thread (or maybe you two can collaborate and have the first ever combined thread! That would be cool!...you just need to buy a drone)
Originally Posted by M. Requin
Jon, you crack me up! The purpose was to hide, for sure, and peel for a refinish after all the other work is done. But next comes drive train: torque converter is leaking, TT probably needs attention. etc. Another trip through the wormhole to the dimension of penury...
10-31-2016, 09:17 PM
Where I am now
But the gray will peal off.
Jon, you crack me up! The purpose was to hide, for sure, and peel for a refinish after all the other work is done. But next comes drive train: torque converter is leaking, TT probably needs attention. etc. Another trip through the wormhole to the dimension of penury...
