mhpd31

Ok guys, I have been working on my 1988 944turboS for a few months now, and I am at the end of my rope with no clue where to go from here. I will start from the beggining and add as much detail as possible.

When I bought the car, it had a rough idle at startup, and a slight miss once it was warmed up, but nothing drastic. It also had a shutter from a dead stop. I thought these were all problems that could be fixed with a tune up and routine maintenance. As I planned to modify the car anyway, I figured I would do it all at once. instead the modifications just exaggerated the issues.

Modifications were as follows: (all from Lindsey) Billet replacement non diaphragm BOV , Performance tune up pack (black magwires, plugs), 944T 300rwhp package, 944T Quad M mass air flow meter kit, 4 inch exhaust no cat pre muffler 02 bung, polished tip, Black vaccum hose kit, hoses gaskets, etc etc. I got everything put together and all the earlier problems were GREATLY exaggerated. Rough idle, intermittent backfire, car ran out pretty good with boost, but if I did not come out of the hole above 2000 rpm from a stop the "shutter" would kill the car.

http://www.youtube.com/watch?v=t6YiR6Ef7IY

So I called Dave at Lindsey and we tried everything, over the next few weeks, from new chips(3 different ones in total), to a new mass air flow, we tried things until he ran out of things fo me to try. In the meantime, I was also getting suggestions from guys here and on Pelican, TPS, vaccum leaks, improperly installed intake(I pressure tested it and vaccum), ICV..... So I took the car apart (for the third time) checked every vaccum hose, replaced the TPS, the ICV, rebuilt and cleaned the injectors , rebuilt the throttle body and..... same thing! Idle was a little smoother, backfired a little less, but, same problems, and when you take off, you either have to feather the gas (like its powerless under 2 grand) or come out over 2. If I would disconnect the tps (unplug the harness) the idle smooths right out, and it runs great. I am assuming that this puts it into a default mode, and have not tried to actually drive it this way. I set the TPS where it clicks immediatly as soon as soon as you roll the throttle. Also the fuel pressure is a steady 38 psi.

Last time I worked on the car was 5 days ago, and I found a guy in town who supposedly has a plug for ANY car ever made to do diagnostics, so I was going to drive it down to him. Today was new, I got in started the car, and it died, did this 5 times, runs for 5 seconds and then just dies, if I really play with the pedal and feather the gas I can make it get to about 1800 rpms and run for about a minute then it dies!!!! I don't know what else to do, or try, I AM SO CONFUSED !!!! Will the guy with the scanner be able to diagnose the problem on a car of this age?

slap929

I am assuming that this is an 88 turbo s from your other post. You could also try to make a blink code tester, if it is an 88 turbo, and could see if it codes something.
http://www.lindseyracing.com/mm5/mer...Code=BLINKCODE

carlege

modify a car before fixing the problems associated with it running incorrectly?

Richgreenster

It is frustrating.
Have you tried to put everthing back to stock? You should be able to leave the exaust and wide band O2 sensor but try to put everything else back. If it runs with the stock stuff then at least you have it narrowed down to the aftermarket stuff, if not then it is something else.
A side note: My car was doing the same thing. I cleaned all of the grounds and installed another one from the block to the battery and it fixed my problem. Just an idea.

elargentino

Excellent suggestion here.
Then reinstall the MAF controls you have and run zero load using a timing light.
Maybe you'll see some interesting things.

gpr8er

dude....that thing looks like it's major lean!!

Has the intake manifold been off? Check the intake manifold gaskets. You have an air leak somewhere. That would explain the hesitation and backfiring.

xsboost90

so no cap/rotor?

you unplug the TPS and it idles ok? Did you pull the intake and replace the gaskets? Did you try spraying start fluid "carefully" around the intake gaskets and such to see if there is a leak somewhere. Idle would pick up if there is a leak and the start fluid gets sucked in.

AScholtes

agreed... get yourself a can of carb cleaner and spray around all the gasketed surfaces and vacuum lines. You will know when you found a leak.

Oops...guess xs beat me to it.

mhpd31

Richgreenster, that is an excellent idea. At this point I feel like it is an electrical issue, as my voltage numbers seem to be off on the MAF and change intermittently. My assumption was (yes I know who assumptions are for) that something in the computer was changing the voltages due to another problem, and got caught up on replacing other things (tps, icv, etc...) and did not think that it could be a problem in the wiring itself.
http://www.youtube.com/watch?v=FcXsGcxB_Pc http://www.youtube.com/watch?v=wGNAWWeVrHM

I guess tommorow I will first unplug the TPS, and see if I can get the car to start again. Then replace the ground wire, clean some grounds, then make a blink code tester and see if it shows me anything.

F18Rep

First, there is nothing to scan, Onboard Diagnostics didn't "happen" till mid-90s. There is a test port of sorts but it really just tells you that you have basic faults like TPS disconnected or overboost condition. etc. Maybe excessive knock. I guess I'm not sure but I don't think people use it very often.

Some ideas....

I had a really wierd thing like this happen to my old NA and I finally found a shorted wire going to the ICV. The ICV cable was laying over a clamp that had a barb on the edge and with the engine vibrations, it managed to cut into the wire. It drove me crazy.

You mentioned fuel pressure , do you have any kind of fuel guage on the engine - thinking maybe some kind of particle contamination got into the rail and into the injectors. An injector that sticks open can be really bad even break a block.

Also no mention of a FPR - if it is leaking through the diaphram - fuel gets sucked into the intake making it very rich and erratic. Also might try disconnecting O2 sensor, see if things change. Temp 2 swithc is OK? Knock sensor? Lindsey knows all this far better than most of us though. Take care... Bruce

slap929

Yeah dude, I might not be the most experienced on rennlist, but if you are questioning the TPS that blink code sensor will test two parameters.

4-1 throttle position sensor or wires | Power wire to TPS, ground contact or connection dirty.
4-2 throttle position sensor or wires | TPS bad, but check wires first.

its cheap, you have the port on your car, and it might tell you something. I like porsche's attempt at a diagnostic system prior to ODBII.

mhpd31

And to the other guys, I really appreciate the suggestions, but I have had the intake on and off 3 times, new gaskets each time, and pressure tested with a pressure tester I bought from paragon products. No leaks. Yes I did put a cap and rotor on the car, but not a coil.

Carlege, Yes I was stupid for modifying the car before tracking the "small" problems it had, but I mistakingly thought it was going to be either a vaccum or tune up issue, and did it all at once, LESSON WELL LEARNED!

mhpd31

Hi Bruce, as you can see I havent made it much further into my restoration since I got your excellent tools! I am going in the direction of a short or bad ground somewhere, which terrifies me, as wiring is my biggest weakness!
FPR was in the Lindsey "kit", and the car is running very lean not rich. I did put the fuel pressure gauge on the rail as I was trying to diagnose the problems, but it was after the problems had already presented themselves. I did test the o2 sensor (not the problem). Did not try the temp switch, but it is the same at all temperature ranges (could it still be a problem). And I don't know how to test the knock sensor.

Slap929, gonna make a blink tester tommorow, and see what it shows, thank you for the suggestion.

Black51

It seems to run fine with anything more than 10in/HG of vac pressure. So I'd be leaning towards either an idle problem, or a TPS problem. If it was a vacuum issue, the engine would die as soon as you'd touch the gas. Definitely check to see if there's a blink code indicating a problem. I'd start by checking the cheapest to replace stuff first like wires, plugs, looking into the throttle body... those kinds of things. I wouldn't be surprised to see a blink code for the TPS though.

mikeyoman

Sounds rough - thought mine was bad
(comment deleted - didn't see your video)
Are all 4 plugs firing - maybe check the rotor/cap again ?