Injectors no power to them

[JOMJ87]

I have been working on a XJ and now the injectors don't seem to get power. I am not sure what controls the injector firing but it must be broke. I need to get this thing running so i can sell it cause i don't have time to deal with it nowthat i am leaving early. Thanks for the help and suggestions. oh its a 4.0 auto.

 

Cole

[BLHTAZ]

The ECU is what controls the injectors as far as I know. The ECU's do note fail very often in these trucks, but I have been told that if they do fail...it's typically in the injector circuit.

 

I am not an electrical guru by any means so we'll wait for someone else to either confirm my suspicion or offer something else.

[Pete M]

Have you confirmed that you have spark?

[JOMJ87]

runs on starter fluid like a champ i have done a thorough sweep and narrowed it to the injectors hot side. Has ground on the plugs for the injectors but no power. ooked up a spare injector that had the end removed so you can see it fire and nothing this same tested had worked during the timing problem. Like i said its a all of the sudden thing. I had the timing wrong but had fuel i then fixed the timing and tried to crank without any luck. Was thinking TPS because it controls the injectors pulse rate but it goes into the ECU to do so. Maybe i can borrow a ECU from a buddy and try that?? Any other ideas. Thanks guys.

 

Cole

[Pete M]

If you can borrow a known-good ECU I'd try it and see. :cheers:

[flint54]

There is an auto-shutdown relay in the power distribution center (position E). I think this relay can kill the injector circuit. I have the FSM schematics, but no scanner. You have fuel pressure at the rail - right?

[boman40]

That's my question too, what is your fuel pressure? 39 psig, at your fuel rail tap. if not, did you change your fuel filter in the last year? yes, check your fuel regulator, unplug vaccum line and plug it. check fuel pressure before and after with it running.

if your fuel pressure was low and came up to to 39 psig after unhooking the regulator, replace the regulator. If it stayed low, replace fuel pump. if you replace fuel pump, replace fuel filter to, check regulator again or pressure at fuel rail to make sure you don't have more than one problem. hope this helps

[88XJSport]

There is an auto-shutdown relay in the power distribution center (position E).

91+ only.

[JOMJ87]

There is an auto-shutdown relay in the power distribution center (position E). I think this relay can kill the injector circuit. I have the FSM schematics, but no scanner. You have fuel pressure at the rail - right?

 

I have pressure and floe just no power to the injector. I will look at that relay as well.

 

Cole

[88XJSport]

I will look at that relay as well.

 

Cole

 

don't chase your tail. There is no such relay on an 87.

[flint54]

Agree. Wasn't clear what year he's working on. Sig says 87 MJ, but post just says working on XJ.

 

Back to ECU I suppose.

[Randy in Maine]

Have you tried putting a 12 volt test light (or a noid light if you have one) in the electrical connetion to one of the injectors and withthe coil wire off, have someone try to start it.

 

I think the test light should flicker.

[JOMJ87]

I will try that the ECU borrowing fell thru he had to go out of town this weekend. I may have found one for a good price so i might buy it and see if it works. Man this thing has made me nuts trying to get it going. I am gonna sell it now because i am running out of time to work on it but i want to get it running so it would be worth more.

 

Cole

[JOMJ87]

Is there a difference between the Auto or manual ECU for the 4.0??? I need to know cause the ECU i found is a Manual. Thanks

 

Cole

[Geonovast]

Is there a difference between the Auto or manual ECU for the 4.0??? I need to know cause the ECU i found is a Manual. Thanks

 

Cole

 

Yup.. what year is this xj? I haven't seen it mentioned..

[JOMJ87]

90 xj. So i need a 4.0 automatic ECU?

 

Cole