docmirror

Back to basics for stuff like this. for the engine to run, you need three things; An air-fuel ratio near 13 to 1, compression of at least 6 to 1, and a properly timed spark. For rough running, that usually lets out air-fuel unless it has individual injectors, and you don't. That leaves compression and spark.

Both of these can be checked quickly with about $20 of tools. Remove all plugs, and inspect them for oil fouling, contaminants, white powder, or electrode damage. Reconnect all the plugs to their respective wires, and ground the metal plug side to the cam cover. Use an inexpensive screw in compression tester(can be rented usually) in each hole progressively. Hold down the gas pedal and crank about 3-4 times. Don't watch the gauge, watch the plug for a nice blue spark. Now read the compression gauge. It should be above 150LBs or so. Record the reading, move on to the next cylinder. All cyls should have a blue spark, and compressions should be close to the same value. Total time less than one hour for two guys.

Cheap insurance is to just replace all the plugs while out. If any of the sparks were not blue, consider replacing the wires, cap, rotor. If the symptom is related to heat, it could be a coil breaking down, but the bosch coils are pretty robust. As someone else mentioned, inspect the fan for all blades, and make sure the front crank nut is on tight by tapping the damper.

Then, you can get underneath and check for driveline problems as mentioned by other posters.

BTW - HOO-RAH! Keep your head down, and your 'gun' clean....

Doc

SharkSkin

Easy, easy thing to check: pull off the air tubes so your view of the plug wires is unobstructed. Then, in the darkest place you can manage, start the car and look for sparks along the plug wires and coil wire(s). Have a flashlight handy. Toasted wires could cause what's ailing your shark. This can also lead to plug fouling.

animal8526

all these things my uncle will be checking out on monday. perhaps even sunday if he has time... but, as the issue seemed to first occur in succession with a shift, I am led to belive something drivetraid related broke. we will see, and i will keep everyone posted. about fouled plugs or toasted wires... I have the 928 motorsports ignition wires... has anyone ever had problems with them before?

SharkSkin

Fresh plug wires? Nevermind then. Arcing inside the dist. cap could cause some weird running/vibration, but I assume you replaced that too. If the green wire from the distributor is baked to a brown color, it could be a source of problems, but usually the car just dies when that wire goes bad.

animal8526

no, I didnt change the distributor cap then also... shoulda, but didnt... it will all be looked into. although, untill I have reason to think otherwise, I am preparing for the worst. anything drivetrain related is what I consider the worst. that little green wire is like 928 achilles heel, or what? I have heard a ton about it. seems that anytime anyone has ANY running problems, someone suggest looking at that bugger. well, perhaps this is a good time to post on another issue the car has, at least had, last I knew...

for a while, I went through a series of rough runnings with the car... progressivly getting worse. symptoms were stumbling, then the engine would die... eventually it got to the point where I would be drving along, enjoying myself, and hit a bump, and the car would die... then, I could get it to start, but it ran rough as hell, and would die if I hit the gas. after a few days of checking small stuff and scrathing my head (mind you, this was all without rennlist, and just my uncle and I trouble shooting) I had the bright idea that the car ran bad and died if you gave it gas...

Viola! some reason, the car thought it was getting too much fuel, and upon giving it more fuel, it decided to die... a stroke of genious, or luck, led me to unplug the MAF... low and behold, she ran... rich as anything (spitting fuel out the exhaust) but she ran. so, I came to the conclusion either 1.) the MAF was shot and sending bad signal to the LH, or 2.) the LH was shot, and missprocessing a good signal from the MAF (remember, all before rennlist, so alot of this was guessing)... well, ordered new MAF, and used LH brain...

when the parts came in, I installed the MAF first... VRRRRRMMMMM! solution found (damn, I just realized I never re installed that gsket that fell out... what could that screw up?) and I was all happy...

so, here is the deal. car ran after, and ran well, except for... sometimes (usually when still cold, but occasionally at random) you go to give her gas WOT and she stumbles... major hesitation... like she isnt getting the fuel. ease off, give her some time, and usually all returns to normal. anycase, anyone have any ideas?

PS... I have a used LH sitting around... anyone ever needs a tester, I got you covered. and, to anyone who bothered to read that novel I just wrote, thanks for your time. 3-5 minutes you will never get back. sorry

MGW-Fla

If the P dealer can't figure it out to your satisfaction & even if they say they did figure it out, I say take it to Gretch when you make it back state side & let him give it a thorough going over. He'll sort thru it & you'll on your way to happy driving again soon. Thanks for all you do to allow all of us to enjoy the freedoms that we have!

And definately keep your head down!!

animal8526

I just PM'd gretch this morning and am waiting on a response... I am hoping he doesnt mind getting started with my uncle before I make it home... each day she is being fixed, is a day I am not driving her... at 15 days home, I am looking at 7% of my time with my baby for each day I am not in the drivers seat... ouch!

And you are welcome, and thank you. it is my pleasure to serve you fine people. you guys have no idea what your support means to all of us. home in 1 week... hell yeah!

Kevin Michael

Tim, did you check the aux. fan in front of the ac condenser?I had a crack in one of the fan blades on my 1980 and it was flexing under hard acceleration. Let me tell you it felt like the whole car was going to shake apart! To anyone whose ever had this happen they can tell you the shake is intense. New fan (had laying around) and smooth as glass again. Kevin

Kevin Michael

EDIT Under hard acceleration meant getting the car hot enough to activate the aux. fan.

animal8526

Kevin...that fan thing is just what it feels like...had one go in a cuda i had...not fun if you like keeping your teeth in yur head...i did check the fan for missing blades but this monday ill be checking everthing real good...the FANs first. that said Cuda i broke both mounts at once wedged the motor sideways in the engine compartment(doing a holeshot, after putting a used motor in from what i found out later to be an agressive drag car that got wraped around a pole!) but on the way home it shook and vibrated pretty close to this. Monday may be the day of truth or just the begining.
Docmirror, thanks for your imput, ur check list will be used too...thanks!!
TOMMYTOMASO/ on nephs account.

Warren928

Here is a question. The people who installed the springs may have lifted the car from the rear end to make space while working. Hypothetically if they for some stupid reason started the car while it was supported by the rear end, would that flex the tranny and torque tube enough to cause bearing failure or damage? Obviously the torque tube is not designed for much flex.
If they were having problems putting in the CV joint/boot and decided to start the engine and unlock the tranny from park to rotate it while being jacked up on the wrong spot....It could cause undue stress on the torque tube bearings
.
God forbid! But most mechanics (who have some experience on exotics) assume its safe to jack up a car from the differential, but I never saw that in the 928's owners manual.

Or even just supporting the car without starting it from the differential area, you wonder if that could make problems....?

I am hoping for your sake its something simple like a bad coil, fouled plug or a dirty injector.

tommytomaso

they used a 4 point car lift, iv seen them lift this car and other that i had them look over..they always lift it from the correct lift points. they are not ''porsche mecs'' but they are good (and the most trust worthy mec's iv ever delt with, not to mention iv known them for 20yrs.) but things can happen.
Im running on the premiss this is a wear and tear resulted issue. aka old car run hard and fast equals parts will break..just sh*ty that it happens right after so much has just went into it.

animal8526

if someone is out there with a 81 auto as a parts car, I am going to start getting my ducks in a row now... if anyone has any good drivetrain components they dont need, let me know... perhaps we can work something out

Sab

How is the idle?
Any strange smoke out the tail pipes under load?

tommytomaso

idle is fine, revs fine....but vibrates at all reves and increases with revs....when driving right around 1750 i can find a sweet spot that the vibrations are almost gone. If i can ignore all the vibrations and clanking it dosnt ''feel'' like its lost power, but i did drive it like it was about to explode....i have to pick it up at the dealer today, and get it home. Lucky for me i live real close.