PANZERR

'88 4.0 has been sucking through gas, the exhaust smells very rich and discovered it wont go into closed loop. Idles great but as soon as you touch the throttle it starts dumping gas into the engine. Tried troubleshooting on my own for a while before life caught up and I ran out of free time before taking it to a shop. Shop had it for a few weeks before throwing in the towel and making no progress, TBH the shop kinda seemed like they have no idea what they're doing as I had to provide them with a lot of guidance as well as my personal MT2500 to speed up their troubleshooting process, I don't think anyone there has ever seen let alone worked on an Renix engine before mine. Talked to some local places that work on old jeeps and one guy said the thermostat might be bad or the wrong one was put in, confusing the ECU and keeping it in OL so I put a new 195F in. New NTK O2 sensor (23553) should be here today, shop said they tried a few O2 sensors but made little difference. I still suspect it might be O2 sensor related, need to dig up some threads I found earlier on how to test them, apparently new O2 sensors aren't made like they used to and are known to cause issues.
Things I've looked at so far...

• New cat, no exhaust leaks
• New plugs, injectors, timing should be GTG, don't think its misfiring
• Isn't the ECU, tried some same year spares as well as a later year with no big changes.
• Checked the MAP, TPS is properly adjusted
• Pulled and cleaned the (super gunked up) IAT
• No vacuum leaks as far as I can tell

What else should I look at? How many times do I have to rub the block before Cruiser54 shows up? Tips 1, 2, 3, 5, 6, 7, 8, 9, and 11 have been done.

Jim Malcolm

You made no mention of the Coolant Temperature Sensor...

PANZERR

Replacing that today. Sorry, its hard to keep track at this point

Kuro89

Definitely want to take a look at the renix bible, lots of info in testing sensore.
​​​​​​Iirc OL/CL is determined by the coolant temp sensor located on the radiator(?)

Saudade

On the Renix, the CTS is located on the side of the block under the manifolds. The one in the radiator is the electric fan switch.

Also check this one. https://www.lunghd.com/Tech_Articles...iagnostics.htm

Kuro89

That's where it was, thanks been a while since I worked on a renix.

Saudade

I've had mixed luck with Bosch O2 sensors. I run NTKs now. (even have a few spares).

My '88 tends to fail smog on the first test, I use the readings to determine what I need to fix. I always pass on the 2nd try.

I've been going to the same smog shop for years. Back in 2020, I had to do quite a bit to get it to pass. Since the shop is a certified smog repair station, I asked if they had anyone who could work on these old Jeeps. His response was "You mean, besides you?"

The changes I made in 2020 worked so well I even passed in 2022 on the 1st try (OK, I did seafoam it and check my TPS adjustment before going). My next smog is coming up in June. <fingers crossed>.

dmoe69

It sounds like other than using more gas and not being able to pass emissions test, its running O.K.? I don't know about the MT2500, but the REM will tell you the voltage going to the O2 heater. If the MT2500 doesn't, that might be a good thing to check. The O2 sensor also has its own dedicated ground, you also might want to check that you have continuity there,

PANZERR

LMAO
Yeah I follow almost the exact same process. Fail, tinker with related parts, usually passes second time. Hopefully this NTK helps, Bosch was what I took off.

PANZERR

Other than failing emissions it runs great, just stinky as hell and sucks through gas.
The MT2500 is what the REM was built off of.
I'll trace those wires, approximately where does that ground go?

dmoe69

As I recall, the ground is to the frame aft of the sector box. I moved mine, based on a suggestion on this Forum, to the negative post of the battery. The O2 sensor connector and wires are the last things coming out of the wire harness, I think the ground location should be apparent once you have hands/eyes on it.

PANZERR

Think I fixed it. MT2500 shows the engine going into closed loop and all sensors behaving as expected.
Replaced the Bosch O2 sensor with an NTK 23553 and replaced the temp sensor on the block. While in there it looked like the wires to the sensors in that area were too close to the exhaust manifold and melted some together, possibly creating a short. Cut out and replaced all the wiring/connectors, also added some insulation for good measure.

cruiser54

Saudade

OUTSTANDING!!!!