jej3

Hey All -

My 15 yo son and I are trying to get the final pieces in place on his 1987 924S. Struggling mightily with the Speed and Reference sensor gapping.

Here's a brief chronology....

1. I failed to gap the sensors when engine was off the car. It would not run.
2. I *thought* I gapped the sensors correctly but the bracket must have shifted as both sensors bottomed out on the ring gear teeth (Speed Sensor - D) and the flywheel sensor pin (Ref Sensor - B).
2a. Car fired RIGHT UP but died after about 1 minute and would not re-start. I checked sensors to find the damage to both.
3. Ordered replacement sensors and gapped the speed sensor using the washer technique on one of the old sensors. Car would not run.
4. Ordered Shims (.3 and 2mm) from 944online. Used the .3 shim on gap tool and on speed sensor. Figured this would bring reference sensor closer to flywheel sensor pin. Car tries to fire and after much cranking did run briefly.
4a. I used 2 different DME computers with no behavior change.
4b. I have the Solid State DME relay which triggers the fuel pump to run when in accessory position.

My setup is a little different in my use of the Solid State DME relay AND a Fidanza Flywheel, which I purchased second hand.

I've attempted to measure and have come up with the following:

Ref Sensor Opening (top of bracket) is 72.84mm from top of flywheel (not pin).
Pin height is between 9.8 and 10.2 from flywheel
Ref Sensor height from bracket mounting face to bottom of sensor is 55.8

So...

72.84
- 55.80
----------------
17.04 = Gap between Sensor Bottom and Flywheel
- 10.00
----------------
7.04 = Gap between Sensor and Flywheel Pin


This value, 7.04, seems REALLY high. I do have the 2MM shim but my bracket does not have the shield insert or resemble the newer brackets. I'd prefer to NOT destroy another sensor but am unsure what to do.

Any thoughts on Ref Sensor gap typical values?


I don't question the integrity of the Flywheel Pin as this came from another car which was running and equally feel I've ruled out the DME, the DME relay and the sensors themselves.

The car DID run prior to our major refurbishment project.

Dan Martinic

jej3

Thank you for the feedback, Dan. I hadn't seen the gap on page 13 until your post.

I did some tinkering and I reset the speed sensor gap using the 2mm shim. This dropped the reference sensor to the point where the pin on the flywheel rubbed the masking tape off of my dummy reference sensor. Since I have a .30 mm shim, I am going to shim up the reference sensor and hopefully all will be clear.

Grabbing 30 minutes of wrenching when I can between conference calls so I'll hopefully have an update tonight.

Any other thoughts are welcome!

931guru

Here's a tip: instead of using a metal washer on the speed sensor, use a piece of cardboard that is 0.8 mm thick. After you have set the gap, leave the cardboard in place. Over time, it will erode,without your having to remove and replace the sensor.

jej3

Well, I managed to gap the sensors with the 2mm on the spéed sensor and .30mm shim on reference sensor.* I think the ref sensor is probably about .5 and speed about .9 gap.

Car starts runs with throttle assistance and then dies off throttle.* *As part of our refurbishment, we replaced cylinder head, all engine seals, idle stabilizer valve, all engine sensors except throttle position switch, plugs, wires, vacuum lines, fuel damper, fuel pressure regulator, injectors, etc.

I traced all dme wiring and fixed sensor plugs in engine compartment.* Ohm readings at DME and in the engine compartment are 970-1000.* *I also had to fix a flaky tachometer wire, which made diagnosis of reference sensor fun.* Tachometer is now bouncing.

Anyhow,* looking for guidance on what I should troubleshoot.* *

Dan Martinic

jej3

I've tried a smoke test and will be performing another in the days ahead, as NOTHING was obviously leaking.

I also put a fuel pressure gauge on the rail and it initially read 34-36 with the fuel pump running but engine off. After turning the fuel pump off, the gauge dropped slowly to 20 over a period of 10 minutes. 10 minutes later it was at 15 and an hour later was at 0. I have read another thread about a car not starting and have tested the old Fuel Injectors to see if they were all functioning. They are working so I may swap out the new AC Delco injectors for the old Bosch injectors.

Any other thoughts?

jej3

Bump

Jfrahm

The fuel pressure dropoff does not sound like a big deal. A smoke test sounds good. Check the spark with a spark checker (looking for a weak spark). You can't just look at a plug and tell if the spark is weak. Get the engine to run for a few minutes and do a plug chop, check the plugs, what are they telling us?

T&T Racing

Have you tried to start the engine with the "old" fuel injectors? If so, what is the outcome?

jej3

Hi @T&T Racing - We did try to start with the "old" fuel injectors. We've replaced nearly EVERYTHING (I mean all fuel lines, sensors, ignition equipment, etc...) at this stage.

Smoke tests were inconclusive/negative for any vacuum leaks.
Fuel pressure held strong for MUCH longer with a new FPR and the Old Injectors (although I think it was the new FPR)
We have Tach Bounce and what I believe are properly gapped speed and reference sensors
We have tried both new and old spark wires with no operating difference and we installed a new ignition coil because it wasn't expensive from Amazon.

I am not beyond ruling out I may have a bad sensor and the ONLY two things not replaced are the MAF and the Throttle Position Switch

I will likely get the car into the folks at Broadfoot as I just can't spend anymore time on this (have to focus on my 928) and I honestly wouldn't mind a second set of eyes checking everything we've done.

Still open to suggestions!

T&T Racing

If the engine starts and runs with throttle, then keep the engine running for several minutes and then measure the exhaust header temperature of each individual header with an infrared temperature probe. If there is major variation in temperature, then you have an air leak at the intake manifold to the cylinder head, the one or ones with lowest delta temperature.

When installed the intake manifold to the cylinder head, was each gasket installed properly? There is a notch in each gasket for the fuel injector and I believe one of the cylinders had a different orientation than the other three.

jej3

Thanks, @T&T Racing . I have difficulty keeping it running with throttle. It eventually bogs down and cuts off. Intake gaskets were installed correctly as far as I know. We did have to flip one to match the orientation of the intake.

My gut tells me it is an "Air" issue as I have spark and I have fuel.

T&T Racing

Then disconnect the J boot from the outlet of the AFM. Start the engine and spray fuel into the inlet to the J boot to see if the engine runs better.

Charlie

Years ago one of my 44's had the same symptoms. It would run only while holding throttle open. It turned out to be the hose going from the idle stabilizer to the intake manifold had a leak. I have also seen the hose fitting for this hose pull out of the intake. I remember that I did not find the leak until I removed the intake manifold because the hose is on the bottom side of the manifold.