Interesting no Start Problem.
 

Hi Everyone, I have a situation where my 87 924S stopped running while at idle in my garage.

I have started trouble shooting it to see if I can find the cause. I have already gone through some of the obvious things and have determined that there is a good spark to the plugs, good fuel pressure to the fuel rail, grounds to the engine have been cleaned etc. I tried out a spare DME and a spare ECU as well, since I have them, both to no effect.

What I have run into is this;

I get only around 1.5 volts to the each injector with the ignition switched on. What I have noticed is that when I unplug the Idle Stb Valve I get get the approriate battery voltage to each injector. When it is plugged in I get the 1.5 reading.

The valve itself seems to be OK, I have a spare one of these as well and get the same readings with both.

Interesting, eh? Any ideas? Thanks, Michael

Wow, thats really weird, Maybe something has a bad ground, I dont really know what to say because why would the cold start valve screw with the injectors, What happens if you just put a jumper wire across the plug for the cold start valve, DO the injectors pulse, try connecting a small light bulb into the injector plug and see if they are getting a pulse signal that light should flash when you crank the engine, I fthey dont you have a bad crank sensor and if the crank sensor is bad and the ECU see's no crank then it will stop pulseing the injectors I believe. But as for the voltage change I have no idea. Hope I could help.

Yeah, I have been wondering about the sensors on the crank. I haven't touched tham yet but your suggested tests would be a worthwhile ones for sure. Thanks, Michael

Check the connections on crank and ref sensors - they get corroded frequently - sometimes a little wiggle is all it takes.

Also check condition of ground wire - it goes from negative on battery to the rear of the engine - right under the crank and reference sensor bracket. Also located right next to heater valve - so it tends to corrode.

And an injector will fire on 1.5 volts

AFJuvat

Thanks AFJuvat,

I did indeed clean up the grounds on the rear of the engine. Iwill check out the two ref sensors and see what happens there.

As for the voltage to the injectors, it is not normal to see 1.5 volts reading there, correct?

Thanks Again, Michael.

Well,

with a little further testing it is clear that my injectors are indeed not pulsing. I pulled the two ref sensors out and cleaned them up a bit (they were pretty solied) but the problem persists.

Hmmm...

I guess I will take a look into the Air Flow Meter next and see what I find there.

did you clean each sensor wire's plug/connector or the sensors themselves?

what happens if you undo one of the injector's plug/connector and then try to start it (with only 3 connected)?

Unplug one injector, try starting it, if it starts replace the fuel pressure regulator, do not bridge the stabiliser plug you will damage the DME.
If you are getting spark your sensors are working, try another DMe relay also

When I checked for the pulse of the injectors I did so with the whole fuel rail removed and the injectors sitting in cups to catch any fuel but there was not even a trickle. I will give it a go with one unplugged but I really don't think it is an issue with the pressure regulator.

I tried a different DME (relay) and got no change in the result, perhaps both of my relays are bad; its not unheard of for new ones to be bad, I guess. Actually, the relay I bought is a different brand than the original so maybe it would be wirth trying another one.

I also tried another ECU (DME) and idle stab valve, from spares that I have, but these also resulted in no change.

I really suspect that the trouble resulted from something close to the Idle Stab Valve because when the car died I was pressing down on the three-prong plug to that very valve.

The solution remains elusive. Hmmm....

Any further ideas?

Thanks Much.

Check the cranks sensors, should be 900 ohms, check the wirting loom, the FPR can cause the injectors to shut down due to overcurrent required for the extra pressure, but you usually loose spark at this time, are you getting +12v to one side of the injectors?

Hey, thanks. If you look way back at the start of the post, the heart of the matter was the fact that I only get 1.5 volts at each injector. I can get full battery voltage at the injectors with the Idle Stb Valve unplugged (won't run this way though) but not with it plugged (only the 1.5V).

I do indeed get spark to the plugs so the sensors seem not to be the culprits.

the center pin of that three-prong plug shares the same 12 volt connection as the fuel injectors, all of which come from DME/fuel pump relay terminal 87 red/blue...you could have a broken connector...unplug your DME unit before you inspect the plug/connector per the earlier warning from Martin T

The connections to the Idle Stb Valve are all OK. Nothing broken there. I have, in fact tried a spare DME Relay as well as a spare ECU, all to no effect. The swapping of these items changes nothing on the readings.

I guess, perhaps, its time to go through the wiring itself to find a problem.

This problem is a real drag.

Thanks.

with the DME unit disconnected and the idle valve unplugged and the DME relay pulled, take resistance readings between the 3 pins of the wire plug...should read 'open' all way around...also between the 3 pins to ground (chassis)...again all should read 'open'

also do same for idle valve connector itself...compare the ohms readings with your spare valve

Which three pins are you referring to here? The three slots of the Idle stb Valve connector, correct?

Thanks.

you're right...a 'connector' is female and a 'plug' is male...so I shudda said the idle valve wire 'connector' that goes into the engine harness

then do the same with the plug's 3 male pins on the idle valve itself and compare the resistance readings with your spare valve

Cool, I'll give it a whirl in the morning. Thanks

Just athought have you checked all of your fuses?
Sometimes one will look good and still be NFG, also put dielectric grease on all of the engine elex connections, Stan

good point Stan...I had a fuse once that tested good (zero ohms) looked good, but under load it 'opened'...an invisable hairline crack

I threw it on the roof of some building...I was so ticked...wasted all day

nFg !!

Hmmm....I did go through the fuses but I will take a another peek-couldn't hurt. The diaelectric grease is GREAT STUFF!