Please help me track down this ECU fault!

Richard Burnett

Richard Burnett

New Member
Joined
Mar 25, 2018
Messages
4
Location
Barga, Province of Lucca, Italy
Hi Greetings from Sunny Italy, I have had my TJ for 15 years and replaced most things, the old girl has had a hard, hard life, I keep her going the best I can, but I am a little stumped on this.

I was driving up my forest road and the engine stopped, tried all the usual things and this is where I am:

1. Engine has spark, when primed with fuel - starts and then stops when fuel used.
2. No petrol in fuel rail
3. Pulled Fuel pump from tank - works fine on bench (replaced 12 months ago) :)
4. ASD relay clicking and supplying power
5. Fuel pump relay has power - but does not click, but when I short the common and earth with a jumper - the fuel pump runs ok.
6. All sensors (CPS etc) all check in limits and seem to be working fine.

So I obviously suspect the ECU (But would the ignition fire if the ECU was U/S?), or a wiring issue - is there any check I can make in the Relay holder?

I have swapped all the relays - no click when in the fuel pump position!!

Any pointers would be appreciated as I have to walk out of our farm 2 Miles a day every time we need to get into town!
Thanks for your help!
 
Richard Burnett said:
5. Fuel pump relay has power - but does not click, but when I short the common and earth with a jumper - the fuel pump runs ok.


So I obviously suspect the ECU (But would the ignition fire if the ECU was U/S?), or a wiring issue - is there any check I can make in the Relay holder?

I have swapped all the relays - no click when in the fuel pump position!!

Any pointers would be appreciated as I have to walk out of our farm 2 Miles a day every time we need to get into town!
Thanks for your help!
Click to expand...
Ok I wouldn't go straight to the ECU. Can you keep it running long enough to get a code?
Even so, I would say that you have a wiring problem.
Number 5 above is confusing. If you jump it and run the fuel pump can you get it to start?
I would look for a blockage in the fuel line or trace the exciter for the relay before I would put a ECU in it. In fact I would not change my ECU unless I knew it was bad. I mean I wouldn't replace it to see if it is bad. You are likely to cause more unwanted issues if that wasn't the problem.

It sounds like you are on the right track. Try and figure out why you are not getting fuel to the rail.

BTW your fuel pump can be running but it needs approximately 60PSI to run your Jeep, so if it is running, but not producing that much pressure it wont run.
 
Thanks for the great advice.

The fuel pump is around 6 months old and I have dropped the tank and the unit is currently attached to the wiring but out of the tank - so I can see and here it working (when jumped at the relay)!

I hadn't jumped the relay and tried to started it - as the pump was already taken out at the point, but I I tried fuel directly into the plugs and she fired up as normal and then of course died.

When I jump the common and earth on the relay the pump works as it should, so I assumed that the earth was not being triggered from the ECU, or a bad wire, or earth.

I have not been able to get a code from the jeep for the last year - no idea why, but the TJ is a farm workhorse, so I wasnt that surprised and she ran fine despite not being able to get the code.

There are a few other things wrong - ie no clock spring! Also over the last six months, I had an issue a couple of times when the immobiliser (grey key) seemed to have problems in that the jeep would not start - I disconnected the battery, and it seemed to clear itself and went on as normal - so I wondered if this was an extension to that issue - but would have expected the spark not to be there in that case, rather than just no fuel pump!
 
Well... Sunday afternoon, I took off the ecu from the bulkhead so that I could easily probe the contacts and then put the fuel pump back in the tank and put if all back together. I tested the pump - no go (as expected) then jumped the fuel relay pwer and ground and the pump ran fine and delivered fuel to the fuel rail (as expected).
But no start - so again I checked the spark - now no spark (there was spark before).
So no spark and I guess maybe no signal to the injectors as the plugs are dry as a bone, despite good fuel pressure at the valve.

Suspecting CPS now - seems like a reasonable replacement after 20 plus years of use!!
 
Top Bottom
Back