87XJLIMITED

Here is what I'm working on,1987 XJ 4.0 AW4.

At idle on a cold start it idles normal for a couple of minutes, then the idle will drop down and have a slight miss to it, then it pops back up to normal like a switch flipped, this repeats about every 45 seconds even when fully warmed up. Sometimes it doesn't happen at all and the jeep idles fine. Seems to go away when driven at cruising speed for an hour or so then stopping and letting it idle. When the key is shut off the problem will occur again sometimes and sometimes not

I just bought a Snap on MT2500 yesterday(best tool I've bought in awhile) and I notice that the computer enters closed loop when my idle drops, then when it goes back in to open loop the idle is fine, the problem is that it is going into closed loop around 100 degrees . At 180 degrees it rarely goes into closed loop. Sometimes at cruising speed closed loop stays on, but mostly it is in open loop. Is this a O2 sensor problem or ECU The O2 sensor works like the scanner says it should when in closed loop. I have 5 volts at the coolant sensor on the side of the block and the ground is good. I have done almost every thing in Cruiser's Renix file's including the C101 delete.
I know that I have a thermostat problem cause it gets up to around 176 to 185 degrees cruising down the road. I put a NAPA 195 thermostat in it a month ago. I guess I will see the local Jeep dealer.

Any help would be appreciated.

salad

Your coolant temp sensor could be giving you headaches. Can you verify the engine temp with an IR thermometer?

87XJLIMITED

Can't do it today. But I plan on checking it when I get to work in the morning.

When I disconnect the sensor, according to my scanner instructions, the coolant should read 247 degrees on the scanner, which it did, but it took about a minute to get there, it slowly climbed up . The Renix has 2 coolant sensors, one for the ECU and one for the gauge. The dash gauge sits at or just above the line in the middle between 100 and 210 at operating temp which leads me to believe the ECU coolant sensor is accurate as it reads around 175-183 on my scanner.
I disconnected the sensor and drove the jeep with the ECU believing the coolant temp was 247 degrees and it stayed in open loop.

DFlintstone

My idle cycled until I changed my 02 sensor.....

https://www.cherokeeforum.com/f2/ren...ce-rms-133153/

DFlintstone

Your temp gauge sender is rear-left on the head. Your engine coolant sensor is down under on the left side. The temp switch for the E-Fan is on the radiator.

247* sounds nutty hot. (the E-fan comes on about 217*) And on defrost or with the AC.

Both the IAT on the manifold and the Engine Coolant temp sensor use the same numbers to test, found here> http://www.lunghd.com/Tech_Articles/...iagnostics.htm

Best of luck, and Welcome by the way! You might want to take a peek at Cruisers stuff in my signature.

87XJLIMITED

247 degrees is what the computer thought the temp was because I unplugged the sensor on the LH side of the block. Actual temp was around 175-180 degrees.

Just went to the store, coolant was 89 degree on the scanner and the dash gauge resting at the 100 mark before starting the engine. Within 10 seconds of starting the engine the computer switched to closed loop and then open loop over and over while driving for about 4 minutes till I got parked at the store and shut it off. Coolant was at 131 degrees on the scanner when I shut the engine off and the O2 voltage was a steady 4.92V to 4.62V and didn't move the from the time I started the jeep till I shut it off . On the way back home it went into closed loop a couple of times right off the bat, then stayed in open loop and the O2 voltage dropped slowly to around 2.68V and then hovered around 3.55.

I thought the computer didn't enter closed loop until operating temp (195 degrees) was reached

It is noticeable when driving 25-35 MPH around town when it goes between open loop and closed loop, when it switches to closed loop you can feel the engine bog down a bit.

Also the fan switch in the radiator is by-passed and now runs through a switch in the dash.

cruiser54

Renix generally goes into closed loop quickly, regardless of the coolant temp. How fast is the O2 sensor switching when in closed loop?

DFlintstone

160* might be a number. How are you seeing open/closed loop on that 87?

cruiser54

I've started a REnix with the DRB hooked up when ice cold. Goes into closed loop within 2 minutes or less.

DFlintstone

Me thinks that 02 voltage is too high. Wavering around 2-1/2 would be better. I had a "solid", 5, till I put in the NTK, then got 2-1/2 and my Idle quit cycling.

The Renix 3 wire titinia sensor (variably) grounds the ECU feed, which the ECU then uses to trim the mix. Starting in 91 the 4 wire zirconium works differently, actually "generating" a current for it's PCM. ( I think!)

87XJLIMITED

It isn't moving much like it is supposed to. One time today on an extended drive it was cycling back and forth from high to low volts but not rapidly like it is supposed to.

I didn't realize that Renix enters closed loop so fast, that makes me think I have a bad O2 sensor. The only sensor available through Napa here in town is a Bosch unit. Is that OK? I thought I read somewhere that NTK was the best one to get. Napa lists a NTK but is out of stock and apparently not available from another Napa store.

87XJLIMITED

I bought a used Snap on scanner for $100

cruiser54

They cycle really fast when working properly. Bosch is okay.

DFlintstone

Really. and it tells you weather it's in open or closed loop? I was right up to date, in 1985. Learning here.

Guess it depends on who you talk to. IIRC some like Bosch for the renix and NTK for the later...unclear there. Anyway I went with NTK....I haven't re checked it since I put it in. Napa here gets parts overnight, so you could have it Tuesday.

djb383

The "loop" closes when the O2 sensor is correctly signaling the ECU. Heated O2 sensors start signaling the ECU quickly after start-up when functioning correctly. Our '98 (not Renix of course) enters closed loop very quickly after cold start (according to the ScanGauge) and well before coolant temp is anywhere close to operating temp. I'd suspect a faulty sensor or signal.