924Board.org

[FASTdan]

Ok, so I've been slowly working through the electrics on my new 924S ruling things out as I go.
So far:

Fuel pump relay - now works as I bought a new one. So the fuel pump now runs when cranking.
Subsiquently I have measured the fuel pressure on the fuel rail at 40psi when cranking.
I also have a spark on each ignition lead, however I believe the coil output or 'king' lead is intermitent therefore I intend on getting new leads anyway. However I am not convinced that the spark is the 'right' spark. I have checked the coil resistances and I believe the coil is ok. This may be a speed/reference sensor issue.

The main problem is that the injectors are not firing. nothing at all. I struggle to believe that all 4 would be completely clogged even though the car has stood for approx 3 yrs but someone correct me if im wrong.
I have done many checks on the DME between pins etc as per clarks garage and the manual and all ok so far. I have checked the resistances on the injectors and they appear ok - and likewise I have continuity between the relevant pins on neighbouring injectors (ie 2 x batch fire). Also the voltage on 1 pin is battery voltage when cranking as required.

I have checked the resistances in both speed and reference sensors and they appear ok too - I have yet to check/re-set the gap on these though. I have now got an osciloscope to check the actual outputs of these sensors and should be checking this today.

Assuming my speed/reference sensors are ok, where do I go from there? I'm running out of options! Aside from the DME itself? What other tests can I run?

One other issue. There is a random 'crackling' noise coming from behind the dash - kind of around the center console area behind the clock etc. it will just randomly make this funny noise regardless of ignition key position so long as the battery is connected. Can anyone tell me what this is?
I am worried its a short of some description as the battery seems to go dead over a period despite being what appears to be a good battery (takes a good charge etc). I have only just discovered this but will investigate further today.

Sorry for the essay but any help would be much appreciated.
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1980 924LUX

[924RACR]

Pending outcome of the o-scope test - I can't help but wonder if your injectors may be clogged?

RE: the crackling noise - yes, I'd suspect a short back there, perhaps. Best to open it up and look for bare wires or connectors...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[924guy]

the crackle noise is probably a loose ground lead making contact with a hot wire, not good.. are all your console gauges illuminated? if not it could be one of those, at the radio, or behind one of the idiot lights or switches. even a small electrical gremlin can cause havoc with these cars, but if theres noise, it needs to be found before something ignites. so its well worth the trouble of locating the problem, even if its not main issue.
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Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[FASTdan]

Thanks for the reply guys. I've spent some time today on the car but unfortunately only heard the crackling once!!! So was struggling to even locate where it might be. All dash lights work, all interior toys etc seem to work so Im not sure. The one time it crackled was after the ignition switch had been on for some time.....this one may take some finding. But like you say it needs to be found as it could cause a fire .

So anyway, I tested the sensor outputs and both appear to be ok.

Reference sensor gave the single peak/trough reading and was approx 12v peak to peak - which seems high bearing in mind the 2v requirement? This also flashed on and off the display - ie always the same curve but it wasnt constant, but reading the clarks description im thinking this is ok?

Speed sensor gave approx 6v peak-peak with a nice steady saw tooth so no problems there.

Sooooo, my injectors still dont work!
My problem is i dont understand what to look for on the injectors or injector feed.

With all the injectors unplugged:
I have checked the individual resistances of each injector and all are 2 ohms. I have checked for continuity between 1 pin on the plugs of both 1+2, and 3+4 and they are ok.
With the ignition key switched on I see 12v on one terminal of each feed which then drops to 9.4V when cranking. On the other I see 9.9V with ignition on, dropping to 6.5V on cranking.

Does this sound right? I thought I should be seeing pulses to the injectors? Is there a way i can check for pulses using the oscilliscope? I'm really quite stuck on this one as there doesnt seem to be much documented regarding non-functioning injectors....

Thanks

Dan
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1980 924LUX

[dgz924s]

Does it have a fuel damper? That unit controls injector pulse.

Dal
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Dal Glassinger

[FASTdan]

yes it does, bolted to the fuel rail?

How does that affect injector pulsing?
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1980 924LUX

[dgz924s]

It looks just like the FPR but the damper has a main fuel feed line(screw on) where as the FPR has a return line(clamped on) back to the tank. The damper controls the pulse via pressure as does the FPR. If the damper is not functioning it will not be able to allow fuel to the rail or a lack of fuel/pressure. This is my best way to put it but I am sure there is a bit more to the function or how it controls pulsation.
Not an expensive item so I would change it just to rule it out and if it fixes the issue you are back on the road.

Dal
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Dal Glassinger

[FASTdan]

It started!!! albeit only for a split second because as i suspected there is no oil pressure! So i imediately shut down, but at least I've solved that one.

I spent a long time reading this morning and found a topic on renlist where a guy jumped his injectors back to life by supplying 12v direct to them. This worked a treat. First off they clicked very quietly but soon enough they were clapping away happily!

So new topic on oil pressure.......lol

Thanks for the help chaps!
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1980 924LUX

[Joes924Racer]

I wont cause a fire right away FastDan what-ll happen is the sound changes the from the crackling to a hissing followed by billows
of acrid blue smoke as
all the plastic on the short wires is liquified. Quite a site.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.