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Discussion Starter · #1 ·
The jeep is running rough and has the tendency to stall after the engine is warm.

Background.
The 1987 jeep wrangler 4.2L has a TBI kit installed - purchased from Performance Fuel Injection Systems (pfisys.com). The installation was done in February 2019 and a round trip from Austin to Galveston was undertaken in May 2019. The engine ran perfectly.

In September - a road trip was taken to San Angelo and the stalling problem began long into the trip and became so bad the road trip was cancelled. Cooling the engine completely let me drive normally again - until it happened again - and i was able to return to Austin in two days or so (normally a 3 hour drive).

Since then, the following trouble-shooting steps have been taken.
1- coolant temperature sensor replaced. - $18.00
2 - idle control valve replaced - $18.00
3 - in tank fuel filter - $5.00
4 - in line fuel filter - $5.00
5 - fuel pump pressure test equipment rented (fuel pump produces a consistent 12 psi)
6 - oil pressure switch (since i was replacing sensors anyway) - $9.00
7 - ECM/ECU 1228062 replaced - $64.00
8 - High Performance 12-Volt to 65K Volt HEI Electronic Ignition Distributor Coil Pack - $26.00
9 - Ground wires inspected and contacting surfaces cleaned
10 - Vacuum lines inspected for leaks
11 - Thermal Sleeves placed over fuel lines in the engine compartment - $12.00
12 - Spark Plugs 'Double Platinum' replaced and gaps checked at .035 prior to installation - $25.50
13 - Carburetor adapter plate removed, cleaned, silicone reapplied, and plate reinstalled.
14 - O2 Sensor replaced - $46.00

I haven't touched the wiring harness, but i have inspected the wires for damages and tight connections. Also, I haven't touched the MAP sensor.
Not sure what else there is? What am I missing? Help! Any ideas?
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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If you replaced the plugs with double platinum there could be your issue. 4.2's like to run the cheapest copper core plugs money can buy. Champion 82's or Autolite 985's have worked the best for me. Seriously the more expensive ones make it run like crap, not sure how that ties in the stalling when hot though.
 
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Welcome to the Forum ccanga,

Have you contacted Performance Fuel Injection yet? They might have some insight into your issue.

Are your temp and oil pressure gauges working?

Good Luck, L.M.
 

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The previous two responses are spot on.

Thought #3... Have you pulled any codes from the computer. Possibly looked into an OBD1 scanning program so you can do some diagnostics? I use TunerproRT with a Red River Devil cable to my laptop.
 

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Discussion Starter · #5 ·
the code is flashing '12' which indicates temp sensor - which was the first thing i changed.'

I've looked at all the YouTube links and this stalling problem is not uncommon for the Ford/Chevy style TBI. And the fixes aren't consistent. In fact each item i have changed where items identified as fixes in one or two videos.

my stalling problem seems to happen when the engine is warm and after i have driven up hill. i can make it happen repeatedly. but it also happens at random times that are very inconvenient - as you can imagine.

on the plus side, with all the improvements i have made, (parts, timing, etc) the jeep starts much faster after a stall.
 

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Code 12 is simply "begin codes" if it is a GM based TBI system.


You stated that you replaced the computer. Was this an off the shelf GM 4.3 ECM or one from PCI? Does PCI put a custom tune in them for the specific application?
 

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Had a friend with an old CJ-7. It had the mopar fuel injection kit so a little different than the TBI kit you have. One day he decided to do some maintenance including changing spark plugs. Puts in spark plugs that are spec'd to the CJ-7. Had an issue later like you mention. Some shop recommended that he use spark plugs from a '95 YJ (like the mopar kit). Worked after that. I think the plugs are a different heat range.

Might be worth checking the directions of your TBI kit and see what it says for plugs.
 

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Discussion Starter · #8 ·
I think I have identified the culprit. The ignition module inside the HEI distributor is suppetable to over heating. I am going to replace it with a new one.

As I said. The jeep ran fine for a year and this problem only developed in september. The problem only happens when the engine is hot/normal running temp after an hour or so. Once the engine cools off ot runs normal again.

I can recreate the problem now. (After 3 months of trouble shooting). I am 99.9% sure it is a spark problem and have so far changed the computer, the plugs, and the ignition coil. The only electronic part i haven't changed yet is the ignition module.

When it gets too hot it starts to miss fire and eventually stalls. I accidentally stumbled on a youtube video about this. It was not something I had considered.

I am looking for an after market heat sink to attach to the base of the large style HEI distributor under the module - so far no luck. Maybe the original module was defective?

The new one arrives in a couple of days. I will post the results.
 

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I think I have identified the culprit. The ignition module inside the HEI distributor is suppetable to over heating. I am going to replace it with a new one.

As I said. The jeep ran fine for a year and this problem only developed in september. The problem only happens when the engine is hot/normal running temp after an hour or so. Once the engine cools off ot runs normal again.

I can recreate the problem now. (After 3 months of trouble shooting). I am 99.9% sure it is a spark problem and have so far changed the computer, the plugs, and the ignition coil. The only electronic part i haven't changed yet is the ignition module.

When it gets too hot it starts to miss fire and eventually stalls. I accidentally stumbled on a youtube video about this. It was not something I had considered.

I am looking for an after market heat sink to attach to the base of the large style HEI distributor under the module - so far no luck. Maybe the original module was defective?

The new one arrives in a couple of days. I will post the results.
Good possibility that is it. It is a pretty common failure point with those GM Distributors. I have read that you should get better heat sink grease than what comes with it.
 
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