BF951

Modified post, I after cleaning contacts at fuel pump I now have 50 lb pressure.

If I start checking signal at the injectors should it measrue 12v when it is cranking, is this correct?

I hate to keep cranking it to test as it hasn't had full oil pressure for several years.



Previous post:
Just completed a number of long overdue repairs, turbo, exhaust, cracked headers, leaking oil pan gasket...and just this morning leakign fuel line to the damper. Now I have no fuel pressure at all. The car has not been run in two years...and I am looking for diagnostic help

Checked the fuse in slot 34, it's good.
Tried swaping out DME relay #5 with a new one, no change

Questions:
1. With Key in Op position shouldn't I be able to measure positive 12v signal to leads back at the fuel pump?
2. Is there any other fuse or relay coming into play here?

When I tried to start it on Tuesday I noticed the fuel leak right off so I must have had some pressure at that time, fule rail had filled with fuel after being emply for two years.

What should the next steps be in trying to figure this out?

TIA
Brian

BF951

Took out plugs, they all looked very dark, possibly from sitting or from cranking after sitting. Anyway put in new plugs, verified I had spark on each one before it went in.

In simple terms you only need compression, spark, fuel/air mix. I have 50 psi fule pressure at the rail, I have spark and I have compression. So what comes into play in getting the injectors to send fuel from the rail?

Does anyone know what signal I should be able to read at the injector connector leads?
Any fuses or relays that I can check?

Thanks,
Brian

max_boost951

Do you have a tac bounce?

BF951

Yes, when cranking the engine the needle is bouncing slightly, it's been a few years but it's it seems to be the same as it was before, I don't remember excatly what it used to look like.

Although there was no strange odor to the fuel I did drain it and add fresh gas before trying to start it.

Are you thinking crank reference sensors? Is the bounce a way to tell if they are reading or could they still be bad? Could the iron accumulation eventually rust after years of stilling and need to be cleanded off?

Thanks!

Bri Bro

The signal at the injector will be 12V on one side all the time (ignition on) and the other side (connect to DME) will have a short pulse to ground when cranking, then back to 12VDC. The grounding pulse comes from the DME, the 12V after the pulse is due to the low resistance of the inject passing the 12V through it while it is off. All injector fire at the same time but there are two leads going to the injectors from the DME.

The injector harness has a long history of getting brittle under the insulation near the connectors and cracking when moved which causes a short.

BF951

I tested each of the injector connectors, both contacts in each injector has a 12v signal with the ignition on. I'm trying to rig up my multimeter leads so I can see it from the cockpit to check for a bounce when cranking.

If the DME or reference sensors were bad I wouldn't get even the constant 12v signal would I ?

I'll update soon with the results. I'll verify compression in the cylinders as well.

BF951

Tested the first two injector plugs, reading 12v constant across both leads to ground when cranking the engine.
I am testing each of these in turn between the lead and ground. Am I doing this right or should it be across the leads?

I am a little concerned about the compression, #1 was 170 #2 was 135
what is expected here? Is #2 just low or do I possible have something filling in the gaps in #1 making it go high?

Bri Bro

Lead to ground is OK, one side of the injector should pulse to ground when cranking.

When doing compression the throttle should be held open and it is best to have a warm engine...not happening in this case. The 170 is high for a turbo and all reading should be with 10-20%.

BF951

Looks like I have a bad DME. Tried tapping on it, took it open to review the board, nothing looked horrible but at this age it could be one of the components. I need to find someone to swap DME's to see if that really is the issue.

The search begins, in Northeast PA thi smay not be easy. Thank you for the help Brian.

Regards,
Brian