another case of no-start, suggestions?

[cschmidt]

Folks,

This is the 924S I picked up a few months ago. ( an '88 924S with about 120K on it). It hadn't run in over a year. I fiddled with a few things including some bad gas lines, and in a few hours it started. For the next 3 months of playing with it off and on it always started.

I get it home finally at Christmas. I drive it to work and back 3 or 4 times ( 150 miles round trip) and many many local trips, always started. All together about 1000 miles of driving.

So about 2 weeks ago I head out in the morning, it sputtered and stalled coming out of the neighborhood. I hear a lot of clicking like solenoids - a couple clicks per second - maybe fuel injection. In about 60 seconds it fires back up, I take it home. Next night it starts right up, runs for an hour, multiple starts / stops.

Following morning, it starts right up, I go 3 miles toward the highway and it dies. Same clicking sound heard. This time it will not start. For a bad situation I got about as lucky as you can be. At 6:45 am in a small town, 2 people stop behind me to help. A taxi cab and a guy who used to own a 944 turbo and works at a custom fuel injection shop.

We get the car off the road, I call AAA, the taxi gets me home, I come back with my other car, we get the 924 to the guys fuel injection shop ( he kindly offered to help in his off time for free). I get to work 70 miles away by 10 am.

So in the course of the next week we ( mostly he) ran some diagnostics:

- DME seems ok, swapped in a spare, and tried the jumper. We have fuel and a ( weak) spark.
- he puts a scope on the sensors - both read correct frequency and amplitude while cranking
- tach is bouncing while trying to start.
- signal is coming out of the ECU to the coil ( did not get an amplitude or strength)
- coil is firing
- put a plug in the coil wire and the spark is weak, but it does seem to be firing the correct # of times while cranking.
- we replaced the coil, spark is still weak.
- tried the jump engine and body to battery ground, no difference
- took the cap off and the rotor is ok, we seemed to have a high resistance value across the rotor at first measurement. I double checked it again the other night and it was only a couple of ohms. I ordered a cap and rotor and that will be Friday.
- I tried to start it with starter fluid and still will not catch
- sometimes after cranking, as you let go of the key and it goes to "run" we hear it seem to fire a cylinder or 2.


Any other suggestions or tests? It has been really chilly here in NC and I'm working Saturday, so Sunday will be the next time I get to try something. Thanks again for any advice.

Chuck

[mikepellegrini]

You've covered most everything.

Have you checked the timing and the belt? Even if the belt is still intact, the most common way they fail is by having teeth shear off. In theory, if a few teeth sheared, you could be far enough out of time so you didn't smash any valves, but yet far enough out of time that it wouldn't run.

I'd check the belt carefully. If it's okay, and the engine is still timed properly, then I'd check compression.

How about the plug and coil wires?

You might also check the grounds. A bad or intermittent ground can cause a lot of problems.

How is the battery charge?

Lots a luck!

[Chunkerz]

I'd check the two main grounds on the bell housing along with the ground in the battery box and on the battery terminals. Get some sand paper and sand the connectors, the areas they touch, and the bottom of the nut/bolt holding them on. Sand them until they're so shiny that you can see your face.

[924CarreraGTP]

I'm going to say clogged injectors and bad fuel might be an issue here. Run a half of a can of Berrymans B12 chemtool (not that weak Seafoam crap) and fresh fuel directly into the tank and engage the fuel pump a few times. The chemtool should break it up. I've seen it melt rusty auto paint before my eyes.
+1 on checking the timing belt. Check your airflow sensor connection, speed, and flywheel reference sensors (even though the tach is bouncing) and temperature switch. I would put the original DME back in if it worked. The one you swapped in may be no good or have a short.
Just remember fuel, air, spark, compression. It has to have all of them or no boom boom.

[cschmidt]

So with work and the weather I have been slowly playing with things. Here is the current situation, and would appreciate any suggestions:

- whatever may have been failing, may be worse now. No spark at all.
- replaced cap, rotor, coil and plugs - it is probably time for wires soon anyway so I may get those too.
- We have fuel and have tried starter fluid also, so I don't believe it is fuel related.
- the DME relay checks out fine, fuel pump is running, we have signal coming from the engine computer, tried it with the 3 wire DME jumper, same results
- from the Rennlist site, there were several people that had bad solder joints on the output transistor of the DME computer. I resoldered those yesterday
- rechecked the signal yeterday, there is a signal coming from the computer to the coil, but it is weak. The scope said about 700 ma ( .7 amps). The guy with the fuel injection shop says typical impulses are 5+ amps for a spark. During some of the tests, I have had jumper cables between engine / body and battery ground. Not consistently though.
- I did the Clarks garage ignition coil test and no spark across the plug, on both the old and new coils ( this was with power coming through the computer, I may try it with power hooked up to the battery instead).
- both old and new coils ohm out fine.

- One more thing, I need to go back and find it, is there a minimum speed the engine must be cranking for the computer to fire? The battery was getting low and it was cranking at say 150 rpms. I thought I saw somewhere it had to crank at 225 rpm for the computer to fire? The battery is recharging now, so can retry later.

So for some reason the signal between the computer and coil is limited. Is there a ballast resistor or other component in the circuit here?

Thanks for any guidance or suggestions. There is an Engine Computer repair company I may call and consult with this week.

Chuck

[cschmidt]

So the weather and work and kids have been conspiring to keep me away from the car. I talked with ECU Doctors in FL, and they seemed very nice. They sent the link to the following video to check sensor outputs. Both my sensors passed - around 940 ohms each, 2.2 V at the speed sensor cranking and .1 volts at the reference sensor cranking. All the pins on the DME plug that said ground were checked and had 0-1 ohm of resistance to the battery negative terminal.

How to test a Porsche 944 RPM and TDC sensor


The weather is predicted to be crummy this week and I'm on the road bunch, so I'm going to send the ECU down to ECU Doctors and have them bench check it. We'll see where to go from there.

Part of the fun for me is the learning process. While investigating the sensors I found what appears to be the coolant valve for the heater. My warm/cold selector is sticky and only moves about 1/2 of the overall travel it should - back and forth. Now I know where it is connected! That may be one of the next things to figure out.

Chuck

[TibetanT]

Bad grounds, battery needs replacement?? Are both sensors, speed and reference sensor hooked up okay? Sometimes these connections are not fully seated and cause you grief. Check fuse box too...something may have come loose.

Is there enough fuel getting to the fuel rail ? 32+PSI?

Just a thought. GL

[cschmidt]

Well it just took time with the weather and work and college age daughter drama.... After looking at the sensor video from ECU doctors, it passed all those tests. I tried starting with starting fluid..., the issue was no spark. I took apart the computer and resoldered the output transistor, still no spark. I checked grounds. So I sent the computer to ECU Doctors for an evaluation. They found multiple other bad solder joints - at least that was the diagnosis given back to me. They repaired it and send it back. Installed the computer and it started first time. Been running around town all day in the car and all seems well for the moment.

It is great to be driving the car again. Thanks for the suggestions and support.

Chuck