1986 2.5 Rough Low Idle

[CaffeineTripp]

I'll start off with the problem; the Jeep won't idle at all. Stalls. Takes a bit to start and will only start when throttle is held down. Throttle must be held down to keep the Jeep idling. Seems to have a miss until you hit ~1800 RPM. Smooth from 1800 RPM +. Cap, rotor, plugs, wires are within a year old, checked gap on plugs and it's fine. Checked for some vacuum leaks at obvious points, but a bit hard to do without a fogger machine.

I've searched and came across a few options; clean the IAC, check TPS voltage on positive and sending, test MAP voltage, solder C101 connector (if it is a problem for the 1986 as well as the 1987 2.5s).

Problem is, most of everything I've found is for a 1987 and above engine, not sure how much readings and connection points differ between the '86 and '87+ model years. What I've found for the sensor readings is this:

MAP: 4.5-5.0 volts with KOEO

TPS: ~4.82 V Positive, 17% for Output to ECU

Fuel Pressure: 9-13 lbs (though I've also seen 6-9 for TBI equipped)

[cruiser54]

Make very sure the ground strap from the head to the firewall is good. I would replace it with a #4AWG cable if it were me. The firewall paint interferes with it's connection also. Remove the 15mm bolt and scrape the paint off under the strap before you do anything else.

[CaffeineTripp]

I've done that part alway when I was going through cleaning many of the grounds I could find. Got the main battery ground cleaned on the block, head to firewall ground, and a few others. The ground strap is still in quite goos condition with no fraying.

[CaffeineTripp]

Checked out the sensors today before work. The MAP sensor is reading at A-C: 5.02, B-C: 5.0. A-C: 1.479 Ohms constant.

The TPS, which I believe to be on the backside of the TB closest to the firewall: A-C: 4.97, B-C: 5.02.

All of the voltage readings were taken at KOEO.

The front sensor, which I thought housed the IAC valve, apparently isn't much of a valve whatsoever, more or less filled with gears, a stator much like that of the , and not nearly as much of a pain to disassemble as the TPS is on the back of the throttle body.

There is also a sensor, what I believe to be a sensor, at the back of the head on the driver's side. Can't for the life of me remember what color wire that was leading to it was, was unplugged. Coolant temperature of some sort? Driver's side left, at the very rear.

Also, possibly fixed a massive vacuum leak near the throttle body itself; an L shaped vacuum hose which connected directly to the intake manifold and a small, black vacuum line. Needed to be removed to access the TPS.

As of now, she runs brilliantly, though it's still a bit of a trouble since I didn't really do anything.

[cruiser54]

Spray some carb cleaner around the rest of the hoses near the throttle body wit it running. Notorious leakers.

[CaffeineTripp]

Seems the going assessment. Eventually I'll end up taking off the intake manifold and the exhaust manifold and rebuilding the throttle body with all new gaskets and seals, cleaning up everything on that side and getting rid of useless vacuum hoses and lines to keep it simple and straight forward. Only the things that are necessary for the engine to run and run well will I keep hooked up. Be nice to get rid of all the rats nest of vac lines/hoses.

In any case, to a question that I had above, this C101 connector, is this also a problem on the '86s, or did Jeep for some reason get it right for the first two years of production and then get lazy thereafter?

As to checking for vacuum leaks, besides using carb cleaner, soapy water, propane, or something else like that, I've heard that if you use a fog machine that can work as well, but then there's the risk of harming an internal sensors; MAP, O2, IAT. It's something that I've looked into purchasing so I can have the capability to find every single leak that the 2.5 has rather than going through all the hoses with carb cleaner in hopes that I can hear/see anything going on with the truck as the engine's loud as hell.

[JENSSEN]

My 88 2.5L was doing the same,... It had one loose intake manifold bolt, tightened it up and it's all good

[cruiser54]

Throttle body cleaner is perfectly safe to be spraying around.

 

There was never a good C101 connector.

[CaffeineTripp]

Throttle body cleaner is perfectly safe to be spraying around.

 

There was never a good C101 connector.

 

Not that I'm so much worried about spraying TB cleaner on anything inside the engine bay, just that it's a bit hard to find any leaks on vacuum hoses and lines with it, along with carb cleaner and soapy water.

So I'm under the assumption that no matter the year or engine, all Comanches had the C101 connector that was just plain ol' junk?

[cruiser54]

Throttle body cleaner is perfectly safe to be spraying around.

 

There was never a good C101 connector.

 

Not that I'm so much worried about spraying TB cleaner on anything inside the engine bay, just that it's a bit hard to find any leaks on vacuum hoses and lines with it, along with carb cleaner and soapy water.

So I'm under the assumption that no matter the year or engine, all Comanches had the C101 connector that was just plain ol' junk?

 

In 89 they did away with the c101.

 

TB cleaner should work perfectly to find any leaks.

[Comanche1987]

is there a thread explaining this c101 connector?

[cruiser54]

I bet this will work for you.

 

Renix Jeep C101 Connector Refreshing

 

 

The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

 

Almost every critical signal between the engine sensors, injectors, and the ECU travel the path through the C101.

 

The C101 is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.

Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.

 

If you have a small pick or dental tool tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter. Apply a true dielectric grease, not the stuff that came with your brake pads, to the connection and bolt it back together.

 

 

 

Revised 11-29-2011