Jump to content

Another "heat Soak" Thread

Recommended Posts

1988 Pioneer 4wd, 4.0l, 5 speed. Motor is stock with 240k miles on the clock. The only modification is the EGR has been disabled and a valve cover from a 92 XJ installed.


I've read every heat soak thread on CC, tried a lot of stuff but still have hard starting and rough idle issues when motor gets hot.

It started last summer when it was hot out and only happened occasionally but now it pretty much does it all the time, even though the air temp is cold.


Once the motor is warmed up, subsequent starts are hard and the idle is rough, pretty much like it's missing on one or two cylinders. It smooths out when you start accelerating and driving but still idles rough when you come to a stop. Runs like a top when driving down the road.


History of work completed within last year:

- New dizzy with cam pos sensor, dist cap

- New timing chain/gears

- New plugs and wires

- Rebuilt, Precision, 4 hole injectors

- Cleaned TB, IAC, and cleaned/adjusted TPS

- New fuel filter

- New knock sensor


Within the last two weeks:

- Swapped MAP, CPS, coil / ICM

- Tested coolant temp sensor, was good

- Bypassed fuel pump resistor

- Cleaned and tightened dip stick ground stud and terminals

- Checked connectors/pins on most of the sensors listed above

- Tightened intake bolts


I'm getting a fuel pressure test gauge Saturday to check out the pressure when warm, also going to insulate the injectors in case they are getting over heated. If FP is good, I'm not sure what direction I'll go then, maybe pull the wiring harness apart and start checking for broken or chaffed wires.


Any other ideas from the Renix gurus? Like I said, I've searched but I'm running out of ideas.

Link to comment
Share on other sites

Ever cleaned your C101 connector?

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, ECU, and some to the TCU, travel this path through the C101 connector.

The C101 connector 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 before bolting both halves back together.


Revised 07-17-2012

Link to comment
Share on other sites

Here's another good test to do:


Cruiser’s Renix Sensor Ground Test


This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.

Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.

Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.

Revised 06/12/2012

Link to comment
Share on other sites

The sensor ground test is quite important.


I don't believe you've got a heat soak issue BTW.


Thanks, I'll be checking the sensor ground. Maybe technically not a "heat soak" issue but definitely a heat issue. Only happens when the engine warms up and the higher the OAT the worse it gets.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...