Hello, I have been working on my Explorer for several days and need some help.
It was running ok a few days ago and when I tried to start it one morning it would turn over fine but not fire. Here is some info.

1 The pump is priming and I changed the fuel filter today and haven't checked the fuel pressure at the test valve with a guage but when I push the pin in there is a lot of pressure.

2 I pulled a plug and there is no gas on the plug (It should be very wet by now)
I checked for spark and I have spark.

3 So I have fuel at the rail and spark but no spark.

Is there a easy connector that I can check the voltage and pulse (I have a O scope) ?
It appears the injectors are not firing.

I checked the connection on the crank sensor but don't know if it is ok and not sure where the cam sensor is. I have been reading for days here and I am at wits end. Any help will be greatly appreciated.
Thanks, Mike
mike@L2Speed.net

 

If memory servers me, with the key on, the injectors should ALL have 12volts standing on them (coil pack too). The other lead (1 per side) is pulsed to ground by the PCM to squirt in each shot of fuel.
If no 12 volts, check the PCM Power relay. If no ground when cranking, then the PCM could be shot.
Doubt you will be able to get a stable trigger the "O" scope on the crank sensor at cranking speeds. If you do, it will only be a low voltage fluctuation unless you get lucky with the settings.
There is no cam sensor on the 91's.

 

Dialtone, thanks for the reply. I am going crazy on this. Where should I check for the 12v on the injectors? They are impossible to get to. Where is the PCM relay? Thanks, Mike

 

Pull the plug on any 1 of the 6 you can get to and check for 12 volts. If 1 has it, most likely they all do as I think it is a series cconnection from the first to the last. The pulse lead is bank dependant. 1 for each side.
You can also try sticking a straight pin thru the wire insulation to get a test point.

Relays (3 of them) are UNDER the fuse box on the right fender. ( PCM Power, Fuel Pump, Wide Open Throttle) Orignal factory relays are keyed so difficult to interchange, replacements (as from Autozone $12.00 each I think) are universal.
Just buy 3 and save yourself some grief trying to figure out which is which.

 

Update: Just checked and I have 12v on one side of the injectors. Not sure the best way to check the side that is grounded by the computer. Any ideas?

 

Backprobe the harness at the injector....

 

I just checked the pulse side of the injector and I am NOT getting any ground pulse from the eec when cranking. Is there any sensors or anything that would disable the pulse from the eec? I did spray starting fluid in the intake and it did run ok so I just need the injectors to get the ground pulse.

 

This is definately EEC related. Time to start probing the leads at the EEC connector for power and ground supplies, tach lead input, etc.
At this point, you need a good wiring diagram. Hayens manual on these is essential.

One shot in the dark might be to remove the battery, and inspect the wiring to the electronic spark module. Tach lead originates there.

 

I have a wiring diagram from autozone. Also I notice the tach is moving when I crank it. Another interesting thing is, The night this quit working there was a real bad thunderstorm with lots of lightning and thunder and this car was sitting outside. Don't know if there is a connection. I did spray starting fluid in today and it started fine. Just not getting the ground pulse from the eec to fire the injectors.

 

Have you run the self-tests, yet?

I'm not sure of the complete sequence of events, but I expect the computer needs to see PIP/TACH from the ICM/CKP before it will fire the injectors. If the computer isn't seeing those signals, it may set an appropriate trouble code (CM 14/18/other). If the computer is seeing the problem and sets a trouble code, that would help narrow down where the problem is occuring.

Have you checked the computer's grounds. If the computer "throws the switch" but there isn't a good connection between the computer and the negative battery post, it will look as if the computer didn't do anything.

 

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I haven't checked for codes yet. I didn't think there would be any if the engine don't start. I guess what I know for sure right now is it will start with starter fluid no problem and I am not seeing any ground pulse from the computer. Can you tell me where the ICM is located? Thanks, Mike

 

MrShorty, also I thought I would mention that the tach on the dash moves when I crank it over.

 

The tach on the dash is not the PCM, so just because the dash gauge is seeing the TACH signal doesn't mean the PCM is seeing it.

If the computer can see that you are trying to start the engine, and it can see a reason why the engine won't start, it should set a trouble code in CM to at least get you pointed in the right direction.

On my '92, the ICM is located to the right of the radiator in front of the battery.

 

Mrshorty, Thanks for the info. I'm waiting for it to stop raining here (in Iowa) so I can go out and work on it. Do you know what conditions or sensors would cause the PCM to not send the injector pulses? I know once I get those pulses back I will be running. With starter fluid it started fine. Thanks for all your help. I live out in the country here so I'm kind of on my own on this. This forum has helped a lot. I have been reading posts for days. Mike

 

you need to check codes before you start replacing things.

i vote for a bad ground in the fuel pump wiring somewhere.