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1997 TJ 4.0 ECM not working

GyroRon

New Member
Joined
Jul 22, 2019
Messages
5
Location
Fort Mill SC
Our jeep has always been weird to start since we got it a year or two ago... If you hop in and turn the key to crank it, it will turn over but not start. If you crank for a few seconds and let off, and then recrank it will usually fire right up. Sometimes it takes a third crank to fire up, but it has always started and normally it just takes two crankings to get it to run. I posted about that here before and was told it is likely something with the fuel pump or the fuel rail letting pressure escape while parked.

So the wife took the jeep to the grocery store this past weekend and she says as she is pulling into a parking spot the engine just died. Its never just died before like that.... When she got done shopping and tried to crank it so she could go home it would crank, but not fire up, no matter how many times she tried.

She called me, I came up and tried to crank it, still no luck. I pulled and checked all the fuses, nothing blown... checked the relay for the fuel pump, swapped it with other relays, still no starting. Relay never clicked either as you turned the key or cranked, which was a sign something else was wrong.

Towed it to a local garage, they finally got to look at it yesterday. They said the ECM is no good. Said it isn't firing the ignition or energizing the fuel pump etc.... said it isn't sending out proper ground etc....

Apparently finding a replacement ECM is not easy, only a few places I can find online that have them and they are basically used " refurbished " computers and range from 300$-500$

Any advise on where to get a good reliable ECM would be appreciated.
 
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SkylinesSuck

TJ Expert
Supporting Member
Joined
Mar 28, 2020
Messages
3,278
Location
Northern VA
I don't like your shop's trouble shooting. Many TJ's have wiring harness issue that can present as PCM issues. I would first see if you can find a friend with an earlier TJ and swap out the PCM to see if that fixes it. Earlier models also can swap PCM's without any issues from what I can tell. I have in mind. Check FB marketplace and CL for somebody parting out a 97/98 model and grab a used one to test. I'd grab the entire wiring harness as well as their's a good chance that's the actual issue.
 
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CharlesHS

TJ Expert
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Lifetime Supporting Member
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Mar 10, 2020
Messages
4,970
Location
Jacksonville FL, Quezon Philippines
While the ECM having a problem could be the issue; check the less expensive things first.
I would disconnect the (3) 32 pin harness connectors from the ECM and check the pins and prongs for oxidation. When you reinsert the harness connectors into the ECM receptacles; make sure they snap in snugly.
Now test to see if your Jeep will restart.
Another source of problems is the wiring harness that goes around the back of the valve cover near the head bolt; the wiring can rub thru shorting out wiring signals.
Check the ground harness that attaches to the engine block on the passenger side to the left of the oil filter; ensure its clean and tight.
 

tworley

garagequeen
Supporting Member
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Joined
May 23, 2018
Messages
7,008
Location
Arvada, CO
Mechanics will blame the computer when they cant find what is wrong. Engine needs three things to start; air, fuel, and spark. Spray a little starting fluid in the throttle body and see if it will start for a second. If so, then you know you have a fuel delivery issue. Pull a spark plug and/or the coil plug and turn the ignition on, do you see a spark? If not, well now you know there an ignition problem.

FWIW--the fact that you previously had to turn the key on several times to start it in the past indicates the fuel pump.
 

Wranglerfix

TJ Enthusiast
Supporting Vendor
Lifetime Supporting Member
Joined
May 2, 2019
Messages
745
Location
Hollywood, Fl
@GyroRon Is the Jeep throwing any codes? Was the CEL on prior to it dying?
I would take the connectors off like @CharlesHS said. Spray a quick shot of contact cleaner on the connectors as it removes dirt, etc and very quick evaporation.

You can call me to further discuss at 866-888-7710.

Thanks,

Mark
 
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Jeeper123

New Member
Joined
Jun 26, 2019
Messages
3
Location
Hamilton Ontario
Hey guys,

I am having a similar problem but my Jeep is throwing codes. P0340 P1492 P1391 P0443. I am thinking it has something to do with the camshaft sensor not being happy or the ECM is not working properly. It’s a super weird intermittent problem where it works perfectly fine then if it stalls or something it can be a nightmare to start again the only success I’ve had to get it started is undoing the battery and waiting for a while then re plugging it back in. Also I put in a brand new distributor last year so the camshaft sensor is new and it never fixed my problem. I’ve checked the wiring harness and grounds is the ecm likely to be the culprit is there any more tests I should do to diag this issue. I need it solved as I almost got stuck out on a trail this weekend.

Thanks,
Ryan
 

01browce

New Member
Supporting Member
Joined
Apr 23, 2022
Messages
13
Location
Hilliard Florida
If YOU decide you need the ECM, I am 3-4 weeks on my new one from Wranglerfix. I can testify that mine works like a CHAMP. If that's the direction YOU decide to go in I highly recommend them due to Mark's service, shipping and oh yeah, it fixed my ECM problems.

20220622_200015.jpg
 

Wranglerfix

TJ Enthusiast
Supporting Vendor
Lifetime Supporting Member
Joined
May 2, 2019
Messages
745
Location
Hollywood, Fl
If YOU decide you need the ECM, I am 3-4 weeks on my new one from Wranglerfix. I can testify that mine works like a CHAMP. If that's the direction YOU decide to go in I highly recommend them due to Mark's service, shipping and oh yeah, it fixed my ECM problems.

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