Caish

The Money Pit is coming together,
I've got a renix issue I can't seem to figure out.
Its idling so/so slight miss, maybe plugs or wires there.
It tries to smooth out just above idle and upper RPM.
Under a load like taking off, and with every shift (5 speed)
rolling back into the throttle it pops back through the intake...
I'm starting to think it might bad injectors. This engine came
out of an 88 XJ with 128k miles and sat for around 10 years
in the peoples back yard.
Any suggestions? Injectors, Knock Sensor, anything else handy?

Molinaribp

my 88 had what sounds like a similar problem after i rebuilt the motor, real smooth under any type of load but as soon as you let off run very poorly even stalled a few times. it turned out my timing was a bit off and the o2 sensor was bad, but after talking to a jeep tech he said that it was pure luck and the dealer he works for doesn't always fix the renix's.

Caish

Googling up my issue I found another reference to the O2 sensor.
I got a spare, I think I'll change it out in the morning a see what happens.
I also forgot to mention the EGR valve is disconnected and its fully closed. So thats not the issue.

Caish

I've checked about everything I can check.
I'm stumped, guess its going to go visit the
shop and see what they can figure out.
I've got two of everything except the knock
sensor, I've used multi tester on all the
sensors and can't seem to find the issue.

On a side not it will idle a minute or two
then die but the injectors keep clicking
like it was still running.

Caish

Ok, I found the Renix manual and have been reading over it.
I noticed that it says the TPS for an Automatic, is different from the standard shift model . Its a Dual Function sensor.

I'm working if this might be a cause for the running issue I have.
Anyone have a clue before I go to tearing it apart again?

Caish

Well after a more little checking, I've deduced the knock sensor maybe bad.
That would explain the rough running.
The one thing I didn't do that might revealed the issue is run a timing light on the it.
But it would make sense if the ECM was slamming the timing from full advance to full retard thinking it is detonating and causing it to run erratic.
That dang sensor is expensive though, $60 I think it is from O'Reillys.
Should have it tomorrow and see what that does for the running.

xj8588

well can i tell you how hard it is to diagnos renix problems. i have a few jeeps, one being an 88 and i had simalar problems, idle related anyways. instead of throwing money at sensors (im guilty of this as well) did you check and recheck/clean and or replace all of the ground wires/ connections? this made a huge difference to my jeeps and from what i know/ have learned this is one of the most common problems with te older renix era jeeps. hope you get it all worked out. hang in there lol

Caish

Thanks for the tip on the ground,
I've checked all the grounds and even for the sake of argument, I ran a ground from the battery to the sensor ground on the diagnostic port.
So that idea 98% ruled out.

xj8588

well i just figured it might help if you hvent checked them all over at least once. as far as i can read, you pretty much changed everything else out. so i hope the knock sensor fixes things for you. i might check mine out one of these days as well... sill not running perfect. now that i think about it did you check the tps ground? or run the ground wire from it to a good engine ground directly? just trying to think of things that i have heard or tryed. good luck

Caish

There is one other thing that makes me think its the knock sensor. But I can't verify it.
The injectors are not turning off when the engine dies and causes it to load up. Silly I know, but I was thinking that maybe the ECM used the knock sensor to determine if the engine is running.
I know it sounds strange considering that it has a CPS and Cam sensor to tell it the same thing.

5-90

The knock sensor doesn't do anything unless there's a problem - you can disconnect it entirely and the engine will run fine, as long as it isn't knocking.

The "other side" of the RENIX A/T TPS is there for the TCU, and has nothing to do with the engine.

What you describe sounds like the distributor is off by one tooth. RENIX is highly adaptable, but it wants a good baseline to work from (idle will stumble and stall, but it will run fine at speed. I just went through this on a job I had here...)

If the engine "sat around," who's to say that someone didn't play with the dizzy and put it back wrong? It's easy enough to work out - lift the dizzy and turn it one tooth anticlockwise (and note that you did so.) If that levels it out, stop there. If it doesn't, lift it again and turn it two teeth clockwise (and so note.) If that levels it out, that's fine. If it doesn't, turn it one tooth anticlockwise again (to eliminate that as a future problem,) and start checking sensors again.

A failed/failing HEGO will typically make the engine run rich - which kills fuel economy, but it will still run fine (dealt with this one as well. The HEGO provides a feedback path for trimming fuel metering - the input signals are provided by the TPS, MAP, and IAT with some input from the CTS. That gets it within a couple of points of where it wants to be, then the HEGO tells the ECU if the fuel is in trim or not.)

The CKP may be getting flaky on you - you can also try unplugging that plug and plugging it back in to "wipe" the contacts clean. It's a three-pole connector with only two wires in it at the back of the manifolds. The CMP will affect starting (it will act like timing is off while the ECU "guesses" which cylinder is coming up,) but it won't affect running.

CKP = CranKshaft Position sensor
CMP = CaMshaft Position sensor
CTS = Coolant Temperature Sensor
HEGO = Heated Exhaust Gas Oxygen sensor
IAT = Intake Air Temperature sensor
MAP = Manifold Aboslute Pressure sensor
TPS = Throttle Position Sensor

Caish

Thanks 5-90....

I went out this morning and pulled the MAP sensor off the parts XJ and changed it for the sake of argument.
Guess what....
It idles now
At random times the idle will stumble a little, but not serious enough to die.
Cracking the throttle open it has a stumble sitting still. Its still there under load too.
If you roll into the throttle gently it will run out but anything more makes it stumble and miss.

I'm going to figure this out! I'm to the point I think its nothing serious.

superj

check your tps setting too. its supposed to read some number while closed on the multimeter. i bet if its off then it will stumble when accelerating.

an easy check too.

Caish

Checked that yesterday was smooth and progressively higher as it was opened. So its not an issue as I was thinking.
I'm starting to ponder if the injectors are just not fueling smooth, they after all did set for close to 10 years.

superj

its possible. pull them and spray them out with some carb cleaner