Hi from Germany

I´m having a problem to start my ´90 5.0 TPI. (TH350 conversion from manual)
It has been sitting for a while in a barn, I fired it up last summer just fine.

Now I could start it only with a shot of brake cleaner inside the throttle body. Right now not even this helps.
It cranks but will not start, except from a few coughs and farts from time to time.

This is what I already checked:
- Injectors have power and ECM signal is there (checked with a test light)
- Fuel pressure is good and stable
- Ignition coil checked according to Haynes values ->OK
- New distributor and rotor
- Spark is at the plugs (timing ?)
- Ignition module has been swapped with another old one, don’t know if this one is good either
- Pickup coil has 750 Ohm, should be ok
- Temperature sensors for coolant and intake air are around 5-7kohms, should be OK.

Other sensors or Idle Air Control Valve should not prevent the engine from starting some how ?

Can there still be a spark with a shot ingnition module ? This is the only thing I have left now…. I´m running out of ideas.
Might also be a temperature / mixture thing because it is around 32°F now.

What about this “crank” circuit with 3A fuse ? This should be active during starting to enrich mixture and oppress error codes ?
I cannot find this anywhere in the circuit drawings.

I appreciate any hints !


So long,

Marc

 

If you didnt stabilise the fuel it will varnish or will be come very hard to burn. You checked for spark thats a good start now you can use a noid light and check for injector pulse or have someone crank it over and touch a injector you will feel it click. Sounds like you need fresh fuel you might have some stick injectors though. You can pull the rubber supply fuel line bye the frame fail and jumper the pump. The fuel pump relay may have a red lead pigtail off of it you can put power to that to run the pump. If you do not have the pigtail ping g in your aldl does the same thing. You should pump out all of this fuel and start with fresh.

 

one way to tell about varnish in fuel is remove fuel filter iad dump it thru a coffee filter then see what your engine is tring to run on . and yes you can have a bad ciol and still have insufficient spark.

 

Hmm, fuel is maybe 2 years old. I think I can rule this out because it fired up perfectly six month ago and also ran after I used brake cleaner when I took it out the garage. I cannot imagine that all 8 injectors died at the same time. Also I did check the ECM signal at the injectors with a test light....

 

6 months is a long time for fuel to change.....especially to accumulate water. I would say drain it and put fresh fuel in it.

 

im the states , I don't keep even my lawn mower gas for more than 3 months.

 

I guess you don´t pay $7 per gallon as we do ? :-)

I just moved a Porsche 924S with maybe 6 year old juice… never had a problem there. (I know this is odd)
But I will check anyway since I´m becoming pretty desperate.

 

 

you always agree with me julie lol

 

Hey.....how did you know it was me????? LOL
when you're right you're right

 

becuse I didn't think you let frank post here ha ha ha

 

Man, you have way too much info,,, going to have to change it up a bit!

Just kidding...we both post

 

Dry cylinders mixed with old fuel and wet plugs = low compression, poor burn, and fouled plugs? Maybe try removing the plugs, crank the motor to clear the cylinders of old fuel, squirt a little oil in each cylinder, install new plugs, put new gas in the tank and try starting it at 30% throttle. if spark is present and no fuel delivery problems it should run.

 

Now I pumped out the old gas, put new in. I also replaced ingnition coil and module.
Took out plugs and cleaned them with a wire brush.
Now it fires but dies immediately after one revolution. If I let the starter turn for a while there is also some misfire. Spark seems to be a bit weak, but not for sure.
Plugs were wet, fuel pressure is stable all the time.

I´m totally out of ideas now.

 

Did you change the Fuel Pump Relay? These are notorious for going bad

 

Oh Plugs wet? What about gas smell or in intake? Is your Fuel Regulator diaphragm bad? Could be leaking fuel and fuel pressure.

 

Fuel pressure is stable. (But it should go down a bit during start ?)
I´ll try to start it with power on the fuel relay prime connection. That should also bypass a possibly bad oil pressure switch which I just found out could be responsible for this starting problem.

I will also check TPS Voltage.

Damn repair manual has more than 800 pages.... should try the bible instead.

 

have you checked for a shorted injector yet? Ohm each injector, should be around 13 ohms. key is to look for one that is much lower than the others.

 

Injectors have all 16Ohms.
I put a test light on one injector during cranking. It fires up fine then it dies, signal at injector is gone, too. After a second or two it fires again with signal at injector and dies.

Since Brake Cleaner doesn´t work anymore I suppose spark is gone too then.

Therefore I think the ECM doesn´t recognize the engine is running.
Could still be the pickup coil, values where good with 750 Ohms, no grounding.

I could not locate the oil pressure fuel pump sensor. But putting 12V on fuel relay didn´t help either. Can somebody confirm this makes a bad oil pressure switch impossible ?

 

Oil pressure switch does not kill the motor if it does not sense pressure or broken/disconnected. It is only a backup to keep the motor running if the relay fails. It is the opposite of what everyone thinks...Not a fail safe.

 

Then it comes down to the question why injector (and probably spark) signal cuts off and comes back during cranking. What can cause this ?

 

No Ideas ? The only thing I have left to swap is the pickup coil. But I´dont think that´s it...

 

Check out my youtube channel for how to check for spark. (klowny1969) I will be making a video on how to do this on an actual thirdgen this weekend. Also when checking the pickup coil you should check it while pulling the vacuum out a bit..or turning the dizzy to see if it sweeps correctly..u could have a break somewhere in the coil..also make sure your ignition wires are getting spark through them..

Check my video for the spark test..once u do that and all is good..then check for consistent fuel pressure that does not drop when cranking..if thats good..then check to see if you have compression..if u know what to listen for you can check it while cranking the motor..if u have compression then check that your ignition timing is correct, does the motor backfire at all?

ALSO do what everybody else is telling u...change the gas to new gas!!!

Please subscribe to my channel on youtube (klowny1969) to get more diagnostic tips..I will be doing alot more thirdgen diagnosing

 

Ok, Im´readdy to burn this piece of junk !

It fires up but dies immediately. Yes, I did change the gas, see above.
TPS is working, MAP is working, ignition cables are good....

I did 2 videos which show that spark signal is at the coil, even shortly after the engine dies. The other video shows the injector signal which disappears when it also stops firing. What can cause this ?

 

I checked the injector pulses again at the ECM. Pulses are there, engine fires, then they disappear. This keeps repeating itself.
I think the ECM doesn´t go from crank mode to run mode or something.
(Repair manual says injector pulse is present under every condition as soon as engine is started, oil pressure switch is said not to be responsible for injector pulses)

Question is whether the ECM is shot or it doesn´t receive the right signal to recognize the engine is turning.
This signal should come from the ignition module as a pulse (or voltage ?).
Can somebody tell me where to look, I cannot identify this on the electrical drawings.

 

The pulse is a 5v square wave on the purple /white wire on the icm to the ecm.

 

This explains why I could not check this with a 12V test light and measured a voltage of 1-2Volts with a standard VOM which makes sense.

So voltage is there… and I Do have a spark. How likely is a faulty ECM ? I´m already thinking to get one from Rockauto, this is the very last thing left.
(Yesterday I changed the pick-up coil which was totally useless….)

I have the impression that injector signal cuts off same moment the engine fires.

 

It sounds like a bad ecm, The odd thing is the 3.1L uses the same ecm and the trouble tree states you can check its icm pulse to the ecm bye hooking a test light to ground and back probing the purple/white wire at the ecm on D8. There is a few things that will stop injector pulse , vats but that wouldn't be consistent like you have. If the tps feedback signal is over 2.5v this is the blue wire of the tps the ecm will be in clear flood mode and will cut the pulse to the injectors. You already checked the injectors for being shorted and shutting off the injector driver so I really think this is a bad ecm. You can unplug all the injectors and use a test light hooked to ground. If you touch the blk/pink and blk/green if the test light is on you have a short to power. I seem to remember the fsm saying if the serial data line is under a certain voltage the ecm is bad but I can not locate the information on that.

 

The ecm ground , sensor ground is located behind the passenger side cylinder head. You might want to just make sure it has a good connection.

 

I finally tryed another ECM without any success.
I cannot locate the ECM ground connection behind the cylinder head. Is this supposed to be accessed from above ? This is killing me.....

 

There is one on each cylinder head stud not easy to get to but yes you access it from the top side.