Stalling Unless Plugged Into Ignition Coil?

[Boltjd]

Hey everybody,

 

I've got a 1988 Comanche Pioneer 4.0 and I've had some trouble with an erratic/rough idle since acquiring it a little over a year ago. It's my daily driver and a bit of a project truck, so I've spent a lot of time restoring it myself. To give some background, this includes new injectors, TPS, CPS, IAC, MAP and O2 sensor, water pump, radiator (as well as converting from closed to open cooling system), water pump, fan clutch, power steering pump, steering box, steering shaft and harmonic balancer. I've also put in a new camshaft, lifters, cylinder head + head gasket and intake/exhaust manifold gasket, as well as new motor mounts, a new fuel pump an. I've installed new coil springs, ball joints, hubs, front and rear shocks and struts, rotors, calipers and pads, even a dual diaphragm booster and updated master cylinder (as well a  as well as a clutch master cylinder) rear drum shoes and hardware, steering linkage and pitman arm, and track bar. I've refreshed the grounds and done a few tune ups, including replacing the distributor, ignition coil and ECM. I even put in an ECU from an '90, per Cruiser54's tips, and even an updated MAT sensor (albeit with a slight modification, as it's basically impossible to find an OE MAT). I've done quite a bit of soldering, whether that includes installing new connectors or pigtails for almost every sensor and every fuel injector, and even refreshing some of Chrysler/Jeep's horrific duct tape 'connections' (photos attached). 

 

Okay, *phew*.

 

So, to the point, a few months ago, I started to experience (at first) intermittent stalling, usually at stoplights, coming to a stop (as one does), and it was concerning, but it would usually start back up after a couple terror-ridden minutes (the truck would crank, but not turn over). Then, one day, it didn't start back up. I had it towed to a local shop, and upon arriving at said shop, I was told that there was a plug that was not plugged in. I was shown a red wire with a connector that I had not seen plugged into anything since buying the truck: I had assumed it was an extraneous connection, probably utilized in a higher option submodel, as the wiring harnesses seem to be universal to each submodel. The mechanic plugged the connector into the ignition coil, which then switched on the fuel pump, seeming to turn the vehicle into 'accesory mode'. He told me that unless I jumped it to some point, I would have to plug and unplug the connector each time I started and then stopped and got out of the vehicle, or my battery would be drained. I've been doing this, and the truck has been running without any stalls since, at the expense of having to plug in and unplug every time I get in or out of the truck. I've scoured wiring diagrams, and it seems that the plug is either the connection for an engine bay light, or an 'ETR' fuse. It runs to the starter relay by way of a green fusible link.

 

Any ideas what this could mean? Any solutions? Also, any ideas what might be causing the rough idle? Possibly a vacuum leak I'm unaware of? (I've also replaced the vacuum lines and I have completed a cylinder compression test, all to satisfactory reading.) I'm at a loss. 

[Ωhm]

21 minutes ago, Boltjd said:

I've scoured wiring diagrams, and it seems that the plug is either the connection for an engine bay light, or an 'ETR' fuse. It runs to the starter relay by way of a green fusible link.

It is the engine bay light (underhood lamp, if equipped) connector.

[87MJTIM]

I agree with Ohm - underhood lamp.  It should not have anything to do with starting or running.

 

If I were you, I would not go back to him (or he may try to sell you muffler ball bearings).

[Eagle]

2 hours ago, Boltjd said:

So, to the point, a few months ago, I started to experience (at first) intermittent stalling, usually at stoplights, coming to a stop (as one does), and it was concerning, but it would usually start back up after a couple terror-ridden minutes (the truck would crank, but not turn over). Then, one day, it didn't start back up. I had it towed to a local shop, and upon arriving at said shop, I was told that there was a plug that was not plugged in. I was shown a red wire with a connector that I had not seen plugged into anything since buying the truck: I had assumed it was an extraneous connection, probably utilized in a higher option submodel, as the wiring harnesses seem to be universal to each submodel. The mechanic plugged the connector into the ignition coil, which then switched on the fuel pump, seeming to turn the vehicle into 'accesory mode'. He told me that unless I jumped it to some point, I would have to plug and unplug the connector each time I started and then stopped and got out of the vehicle, or my battery would be drained. I've been doing this, and the truck has been running without any stalls since, at the expense of having to plug in and unplug every time I get in or out of the truck. I've scoured wiring diagrams, and it seems that the plug is either the connection for an engine bay light, or an 'ETR' fuse. It runs to the starter relay by way of a green fusible link.

 

 

Cranking and "turning over" are the same thing. You mean it would turn over but not start.

 

Plugging in the underhood light should not affect the engine. But ... it's a connection between the electrical system and the body (ground). Have you gone through all the tips relating to upgrading engine grounds in Cruiser54s checklist?

[jdog]

i would suspect a bad coil/icm, also i agree that red wire is for the underhood light

[Boltjd]

54 minutes ago, Eagle said:

 

Cranking and "turning over" are the same thing. You mean it would turn over but not start.

 

Plugging in the underhood light should not affect the engine. But ... it's a connection between the electrical system and the body (ground). Have you gone through all the tips relating to upgrading engine grounds in Cruiser54s checklist?

Alright, well you seem to have gotten the point either way. And yes, I have upgraded engine grounds with the exception of adding an additional ground for the fuel pump (tip #29). Do you have any other idea why there seems to be an 'open loop' (probably not the correct term, but I'm sure you'll correct me haha) which is 'closed' by plugging the underhood light into the ignition coil? Unless it's just a matter of adding additional grounding reinforcement. I actually have not added an additonal ground from the negative battery terminal to a bolt on the chassis above the radiator. 

[jdog]

i would check for power at the coil, if its not there check the ignition switch and the fuse links.

[Ωhm]

If your vehicle STARTS and RUNS with that Engine Compartment Lamp (ECL) connected only, I'd suspect you've lost your I1 voltage feed from the IGN SW.

 

With KEY ON check for voltage (B+) on the following pins:

 

D2_4

 

C213_A

 

[fiatslug87]

 that red wire is not a ground, it's 12v power.

[Boltjd]

On 12/22/2020 at 7:10 PM, Ωhm said:

If your vehicle STARTS and RUNS with that Engine Compartment Lamp (ECL) connected only, I'd suspect you've lost your I1 voltage feed from the IGN SW.

 

With KEY ON check for voltage (B+) on the following pins:

 

D2_4

 

C213_A

 

Alright, I'll give that a shot. If this is the case, would I replace the ignition switch entirely? Or just the specific wire running to the pin or connector running to the coil?

[jdog]

Will just depend, these things have had melted wires at the ignition switch, bad switch or blown fuse links. If it's the last gotta figure out why it blew

[Minuit]

Yep - that's the fun part. You'll have to check that entire circuit for the problem. The ignition switch is a very good first guess.

 

Simple visual inspection that you might want to try before getting the meter out: The ignition switch on these trucks is very prone to developing a bad connection internally and melting the connector, which can cause any number of problems. Many times you can find a bad ignition switch just by looking at it and the connector. To find it, just unplug the ignition switch connectors located under the dash roughly at the midpoint of the steering column on the right side. You're looking for any signs of high heat or physical damage to either the switch or the connector.

 

If that checks good upon a visual inspection, it's time to get the test gear out and find out where the 12V goes away. Note that this does not mean the switch is GOOD, but it does mean that it's probably time to get the voltmeter out and check various places for 12V.

 

The fact that your truck runs when the hood lamp connector is plugged into the ignition exonerates everything but the switched 12V feed to the ignition system for this particular problem. You (and your mechanic) are very lucky that he plugged 12V into something that's happy to receive 12V, or you'd be having MUCH bigger problems right now.

[JimB]

Had a 87 XJ once. Ignition switch (electrical not mechanical one) went to start one day the key would not turn to start position. Tracked it down to the electrical switch it self. There were signs of over heated contacts. Replaced switch and drove away. Tore switch open for fun. Contacts inside were melted.  Fast forward a few years. Driving same XJ and it just died. Coasted to side of road. Had to call for a tow. I was out of town so had it towed to a shop. They ended up having to run a new primary hot wire from starter relay to ignition switch. Fast forward years again. Bought my first MJ. 86 base. Decided to swap everything from 87 XJ to 86 MJ. 4.0 Aw4 Front dif. While moving wiring harness over I discovered where the firewall fuse box connector bolted together the factory primary hot wire had melted from the internal connector. 

 Sorry so long. I would get a wiring diagram. Find where the power wire to the ignition switch is. Take a meter and see if you have power to switch. There should be a constant hot 12v wire there. If no power there vehicle will not start. Quick and easy check. Been there done that.