Jscaramella

Let me begin by saying that I've tried my best in the search box and have used most of not all the advice and previous issues you all have experienced before to get the car on the road.

At this point I have a 50/50% running car. I'm looking to recall some of your experiences should you have run across the same issues pre and post replacement of parts. Just trying to rule out parts before I decide to swap them, and in some cases determine if hay have any cause to the issue.

This is an 86 951 that I purchased a short while ago as a project (Read: bored over the winter and it was only 2500 so what the heck, all labor is done by yours truly, which is free right ? lol )
It has 179,000 miles on it. Dash cluster was changed and shows 125,000

Overall the car was solid with no chassis damage, aside from worn from seats and a sub par repsray. The car had sat idle for 2-3 years which was my only concern.

Since the purchase I have done the following; also note the car is 100% stock aside from the gauge cluster and a B&B muffler.

New Battery
New timing belt service
New fuel lines (front to rear, kind of a nightmare)
Fuel filter
Trans service
Rod Bearing service (all seemed great aside from #2, all were changed)
New battery
Replace Ref and Speed sensor (with washer and correct gap)
Replace DME relay
Replace Boost control valve.
Check all intake boots and hoses
Check and replace where needed vacuum lines.
Converted to manual rack.

My 1st issue was a no start. After some research and reading at clarks ga I replaced the ref and speed sensor, tach bounce returned and I was in biz.

I made 7 round trips to and from work (about 75 miles) and on the 8th the car stumbled as if it were low on fuel and died. It was at temperature and at speed (50-80mph) After some road side head scratching ( removed DME, checked coil and dist cap connections, noticed ground was loose on battery) the car fired and up and I made it to a gas station. At that point the car took 11.5 gallons of fuel. Not sure what the max fuel level is ( i assume about 16 gallons) and I kinda felt like it ran out of fuel and maybe the gauge is bad. However while on the side of the road I lost my tach bounce while cranking a few times. Ref and speed are both tight and the factory connector bracket installed.

When I returned to my shop I shut the car down and made a trip out a few hours later. Start up was fine and on the way back it stumbled and choked so I ruled out the low fuel issue. I slowed up and eventually the car started running ok and I made it back to the shop. At the end of the day I decided to pull it in and check the ground at the bell housing. When I started the car or tired to it stumbled, choked, idled very bad and died. I pulled the vac lines off the fuel rail dampener and they were clean. I had heard when they fail fuel can leak past them into the vac line. They were dry.

After pushing the car inside we removed and cleaned the main bat ground and connection at the back of the motor. The 2nd brown ground down there I assumed to be the fuel injector main ground? The secondary ground strap on the main battery ground cable was also loose (this is the small bolt in the bat compartment), I since tightened that as well.

In any case I've now made 4 trips (60 miles) and on start up no issues, aside from a slight rough idle fluctuation. I have consistent tach bounce etc. My fingers are crossed that it was a ground issue, but I still have that uneasy feeling.

At this point I have a new coil, dist cap, rotor and new plug wires on the way. The cap is very well worn and needs replacement regardless if it points to this issue or not. Now if anyone can tell me if they have had similar issues I would appreciate your advice on what to check next.

Now I did say that the car was 100% stock but I'm suspicious of the DME, in paint marker "white 944 turbo" is written, which leads me to believe its been out or something. I've yet to open it to see if its chipped, but the cars performance levels are not that of a chipped car, having been in both. The tabs that lock the cover don't seem to have ever been bent to open the cover. I'm hoping the DME is not bad, at the same time its about the easiest part to replace. I did check that it was dry down there and that and the ECU plugs are tight. I'm told that when the DME is bad its often not intermittent and the more like a dead car all together.

Does the TPS have any relevance to the car running or is it just a cold start device?
What is the correct idle speed (hot and cold)? I have 1050 when hot and 900-1000 when cold.

I have a spark checker and injector pulse tester to see if I loose fuel should this happen again, I didn't have either on me when it happened last.

Thank you in advance.

fast951

A few simple things that will help you determine if ignition or fuel is the cause. (Make a checklist to go through, as you will be checking a few things when it's not so convenient).

A- Attach a LED (may need a inline resistor) between both terminals on the coil (Black is +12V, Green gets grounded by DME). You can run wires and mount the LED inside the car. When the engine is running (or the coil is getting the signal to fire), the LED will blink.
B- Get a fuel pressure gauge, mount it on the fuel rail (just for testing). When the car is running, record the fuel pressure.

When the car dies:
1- Check the fuel pressure. If too low, you have a fueling issue. May be the DME relay or the fuel pump.
1.2- Jumper the DME relay and crank the engine, if you get fuel pressure, the pump is fine O/W its the problem.
2- Once you check the pressure and it's fine, crank the engine. If the LED blinks, the DME is sending the coil the signal.. If the LED is blinking, I would check the coil and the dist cap & rotor (a simple spark plug test will work).
2.1- If the LED is not blinking, then the DME or the KLR are not sending the signal.
2.1.1 - Unplug the KLR and jumper KLR pin #16 and #9 on the connector (keep KLR disconnected). Crank the engine, if the LED flashes and the engine runs, then the KLR is the problem. (Do not drive car with KLR unplugged)
2.1.2 - If jumpering the KLR pins does not yield a flashing LED, your DME can be the cause.. A crack shorting once hot.. Or Speed/Ref sensors or ....

Hope this helps..

Jscaramella

Thanks. The LED sounds like a cool trick. What should the fuel pressure be normally?
Is there a female thread on the end of the rail?

fast951

Fuel pressure should match your fuel pressure regulator. Stock regulator is 2.5bar.. The goal is to record what the pressure should be when the engine is running, regardless of its value.
There is a cap and ball at the end of the rail, you remove the ball, tap and thread the cap to install the pressure gauge (or if you have a pressure tester, use it). Order a replacement cap if you drill yours, it's best to run with the ball/cap instead of the gauge.. Gauge is for testing...

onspeed

End of the rail is a male thread capped off with a nut. pressure regulator and dampener are cheap enough. I'd go ahead and replace those. Rule out the fuel pump next times it occurs by jumping terminal 30 and 87b on the DME relay. Should be able to hear the pump running if you stick your head under the car near the pump.

Not sure if TPS could cause this. Try unplugging it next time the car dies. Broken AFM might be a culprit as well.

Tank is 21 gallons btw.

Jscaramella

Sounds like the right thing to do IE, the regulator and dampener. I doubt we know how long they intend any of this stuff to last. I've owned a few other Porsches (this is my 1st Turbo) and I'm always amazed at the age of the some of the parts that are still going strong.

I did pull the TPS while trying to diagnose the 1st no start issue, but after having one of the sensors fully corroded I assumed it pointed to the the ref and speed sensors and never checked it again. The TPS in the car is used from a pile of old parts pulled from other 951's. the TPS was missing when I got the car. It started but the idle was all out of whack. I wasn't driving it then either.

I plan to check the TPS again now after having re read some of the symptoms on clarks.

Droops83

The engine will run without the TPS plugged in, and a faulty one will not cause and engine not to restart. The usual failure mode of the TPS is that the idle switch portion fails and gets stuck, and the engine won't rev much past idle.

If the car acts up again I would heed the checklist that John from Vitesse posted, if the loose ground connections were not your issue then your answer lies somewhere in there.

Jscaramella

Thanks for all the posts. I intend to get the car ready for the fuel and ignition tests. I started keeping a diary, which was good advice. Too many variables to remember.