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No spark after engine swap...

Since Im in the middle or going to be on the same track, is the coil bad? It may have already been asked but I didnt want to read 5 pages.

Work back from the plugs to distro to coil to wire to ground etc.
 
Plugs, wires, cap/rotor, coil to cap wire, coil, ignition module, power and grounds to ignition module, CPS, power to CPS, sync sensor, power to sync sensor, and all fuses are all good. The ECU is simply not telling the ignition module, fuel pump, or fuel injectors to do their job.

So gentlemen, where are the 2 grounds for the ECU located? I think one is the smaller black wire that hooks to the dipstick bolt on the rt side of the block. That one seems ok. Where's the other one? I just fondled my Jeep thouroughly and cannot locate a loose/stray wire.

Also, how do I pull the ECU? I'm assuming it's the metal box between the stereo and the gas pedal. I can only see/feel one screw holding it on, but I'm betting there are more. Do I need to remove the "knee blocker" panel?

The grounds would be very easy to test for continuity with the ECU pulled.

Thanks, yet again...
Jared:patriot:
 
Just a thought, but is the flywheel the same? If it's from the wrong EFI system, it won't start ('87 to '90 Renix 4.0 and '91 up HO). If the CPS was still attached to the trans during swap, it may be wrecked.
There are 2 screws on the box. (up top)
 
carnuck said:
Just a thought, but is the flywheel the same? If it's from the wrong EFI system, it won't start ('87 to '90 Renix 4.0 and '91 up HO). If the CPS was still attached to the trans during swap, it may be wrecked.
There are 2 screws on the box. (up top)
Click to expand...
Good post but it's been covered.
 
Yeah, the flywheel is original. We discussed that 4 pages back. Thanks though.

The CPS was fine, but I replaced it anyway to be sure. Only cost 5 bucks for a used one and now I have a trail spare.

The one screw I can see on the ECU is midway up the box toward the rear of the Jeep.

Jared:patriot:
 
i have a a diagram of ecm. it shows pins #11-12 as ground coming off ecm. they are spliced into 1 line that goes to engine ground on engine. a small wire comes off battery ground and ends on body , beside battery badge714
 
Yeah, I found that same diagram from the '88 XJ Factory Service Manual. I just got done pulling the ECU and testing connections.

I have good constant and switched power coming in (both 12.9VDC), and both grounds have less than 2 ohms resistance.

OK - Is there any doubt that I have a bad ECU? All components have tested ok and none of them work. No spark, no fuel injection, so fuel pump cutoff, no nothing.

Any other ideas?

Jared:patriot:
 
I have an ECU from a manual tranny version you can borrow to try.
 
langer1 said:
This is a dumb suggestion but could you have gotten the battery connected backwards?
Click to expand...

Now that just hurts my pride... Naw, the posts are different sizes.

old_man said:
I have an ECU from a manual tranny version you can borrow to try.
Click to expand...

I appreciate that, but Loveland CO is probably a hefty commute from here. It might be cheaper to buy a junkyard ECU than pay for gas to get there.

Thanks though!

Back to this...
langer1 said:
...you need to look at what things tell it not to start the engine.
Click to expand...

What tells the ECU not to start the engine?
 
I was talking about dropping in the mail. You pay postage.
 
What tells the Engine not to start?

1 key on
2 start
3 run
Three different modes, some require different sensor inputs, some have different switching patterns, either switch or relays/circuits.
1 key on, closed loop
2 start closed loop
3 run cold closed loop
4 run warm open loop
5 wide open throttle

Best guess would be a open circuit for pulse (CPS) with the ECU out it would be a good time to check the CPS circuit (wires). I had one broken inside the insulation, near the end of the fuel rail harness, gave me fits figuring it out. The motor rocking back and forth fatigues the wiring in this area.
Second open sensor circuit, there are few that are necessary MAP being one. Don´t really know if the knock sensor is absolutely necessary for closed loop operation or not. According to the book there is like 9 necessary inputs for start. I don´t really know which if any have defaults.
Always possible to short something, the fusible link for the ECU or bend a connector pin, like the harness from the ignition switch to the ECU, which goes all the way around the engine compartment and back to the ECU.
If the ECU is faulty, the first question I´d ask is why and hope it doesn't happen again quick.
The two plugs behind the relay rack, have given me trouble before. Think they are six pin connectors. Line leak through moisture and/or corrosion.
Good luck, been there done that.
 
OK.... I hope you are all sitting down, not running around frantically in front of a computer screen. Here's the latest - apparently I had the electric fan power plugged into the harness end of the coolant temperature sensor plug. I only know what the plug is for because it has the matching color of wires. Apparently, there is a coolant temp sensor (CTS) on the left side of the block below the manifolds on '88 4.0's. The '99 block does not have one :( The plug was laying in the right spot, and it fits directly into the power supply for the electric fan. I'm thinking that supplying 13V to the computers input for the CTS fried it, because after correcting the plug issue, there is no change in my problems. I'm assuming at this point that the ECU is toasted. I'll be getting a new/used one tomorrow and letting you know how sweet it is to hear my XJ run again after 5 months.

Now onto correcting the CTS issue - I searched and found that the coolant drain plug on the side of the block should be the same size/thread as a CTS. Would this be an acceptable location for a CTS? Would it get enough coolant flowing past it to be accurate?

I also wanted to extend a heartfelt THANK YOU:heart: to everyone who has contributed to this thread. There was a wealth of useful, and helpful information presented here, and I appreciate the time spent responding and researching all this for me.

Soooo... hopefully tomorrow evening I'll be reporting our great success at getting this ol' Jeep running again. Honestly - I almost began to part it out.

Thanks again,
Jared :patriot:
 
No, the t-stat housing CTS came on later models. Mine has no sensor whatsoever on the t-stat housing. The plug for the CTS is on the same loom as the knock sensor, and only like 3 inches long. It has to be within 6 inches of the knock sensor or the plug wouldn't reach. My '91 had the sensor on the thermostat housing though. On the '88 there's one CTS on the radiator that controls the fan, there's one on the back of the head that controls the temp gauge, and there's yet another on the block that keeps the ECU informed about temps.

Jared
 
X2 on the block mounted cts. I had to replace that one and the stupid thing was siezed in the block of course.
 
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