Need some thoughts

[eaglescout526]

Ok so the 84 XJ(89 engine harness with an 86 ECU) has been acting up. Badly and Im nearing my wits end with this one.

 

So this problem surfaced after the fuel sending unit swap. I was able to drive to work just fine but driving home was a challenge as in I started losing engine power. It has since progressively gotten worse to where I can not drive more than a 1/4 of a mile from my house without sputtering as if its getting no fuel, spark or air. 

 

I have done rigorous testing, swapping some sensors with new ones I have. I at first thought it was the sending unit again. All logic pointed to that cause it drove fine prior to the swap, no reason it shouldnt drive right going back right? Well I swapped the float to the original assembly and then put it in and guess what? No change.

 

Tested CPS, was below voltage, new one is below voltage, no absolute change. Both even have the same starting pattern. Starts, drives fine, sputters, turn off, restart, starts, dies, restart, no start, wait, restart, starts, runs, dies, wait, restart, starts, drives like nothing happened then the cycle starts over. 

 

Tested TPS and plugged in a new one. Same as above. 

 

Tested MAP, found it below voltage spec running, hot, idle. Same as CPS. Funny enough, REM told me I had a barometric error. Some change but not alot. 

 

Examined spark plugs, rotor, cap, all fine and within normal parameters. Saw nothing in the cylinders.

 

Compared spray patterns of the injector to my MJ, same exact patterns at idle and wide open throttle.

 

Tested O2, same, either unplugged or plugged in and REM shows good vitals for it.

 

The only thing I can think of is fuel pump is dying, yes swapped relays, no change, or the pressure regulator is or has failed and I have no way to check that as I still need to figure out a gauge set up for the 2.5L fuel rail.

 

But theres no fuel leaks, no fuel leaking into the TB, tested damn near every ignition related component and am damn near at a loss. 

 

Thoughts? My guess from all this, its something thats getting heat soaked and failing or its something else that I physically can not see.

 

[pizzaman09]

How are all of your grounds?  Is the engine grounded well?  It wasn't on a Jeep but I've had similar issues with grounds on other vehicles.

[eaglescout526]

1 minute ago, pizzaman09 said:

How are all of your grounds?  Is the engine grounded well?  It wasn't on a Jeep but I've had similar issues with grounds on other vehicles.

Grounds are good and clean. That was one of the first things I did before completing the swap and making sure there wasn’t any resistance. I’ll probably double check them for sanity but grounds to me wouldn’t be a huge cause of it running and driving right until it reaches closed loop or operating temp conditions to just behave like this. 

[Ωhm]

86 ECU looks for WOT switch input. 89 harness connect to a Power Steering Pressure Switch for same input. This is a difference. Not sure if it would cause your issues. 

[eaglescout526]

Just now, Ωhm said:

86 ECU looks for WOT switch input. 89 harness connect to a Power Steering Pressure Switch for same input. This is a difference. Not sure if it would cause your issues. 

I put thoughts on that and when I examined the wiring and pin out for both wiring and ECU of 86 and 87-90, I came to the conclusion that I’d would be fine to run the older ECU as it won’t see the WOT switch but would see it at the power steering. Now I did unplug that while testing and didn’t see any difference at all. 

[Eagle_SX4]

2 hours ago, eaglescout526 said:

I can not drive more than a 1/4 of a mile from my house without sputtering as if its getting no fuel, spark or air. 

 

2 hours ago, eaglescout526 said:

The only thing I can think of is fuel pump is dying

To me this sounds like a fuel pump problem I had similar symptoms when the electric fuel pump went out in my Eagle. (It was carbureted at the time). The fuel pump was running but not enough to keep up with the demand of the engine. In order to get it to a place I could fix it I had shut the engine off long enough to let the fuel pump fill the bowl back up then drove till it died again and repeated until I got off the road.

 

Definitely find a way to check for fuel pressure. Harbor freight sells a fuel injection service kit with fittings to test either a service port or plumb in inline with rubber hose. https://www.harborfreight.com/basic-fuel-injection-service-kit-64939.html

 

 

[eaglescout526]

13 minutes ago, Eagle_SX4 said:

Definitely find a way to check for fuel pressure. Harbor freight sells a fuel injection service kit with fittings to test either a service port or plumb in inline with rubber hose. https://www.harborfreight.com/basic-fuel-injection-service-kit-64939.html

My thoughts too. I’m gonna go get this kit. 
 

But what’s odd to me is if I compare the spray pattern of the injector on both my engines. They look the same. But I guess if to the naked eye they look the same but perhaps on the atom scale, it isn’t. 

[Eagle_SX4]

18 minutes ago, eaglescout526 said:

if I compare the spray pattern of the injector on both my engines. They look the same.

It comes down to pascals law. Basically if you start at a high pressure through an orifice (the fuel injector)but slowly turn down the volume the output will look the same but volume is reduced. (Saw this explained in an old episode of Numbers on CBS season 2 episode 11. I'm not actually good with physics).