Renix Timing Questions

[mud1059]

Jeep was running on the road, a clunk was heard near driver's feet and then the vehicle creeped to idle and ran like crap above that.

Speed up 10 months, nobody can figure this POS out. I've personally spent several hours searching and acquiring tons of knowledge to no avail.

It idles great. When gas is applied it won't go above ~900 RPMs runs like ass, missing and all the sort. I'm no mechanic, but it seems like timing issues. So far:

Cap
Rotor
Wires
CKS
MAP
TPS
O2
Grounds
All test good. Didn't test IAC as it idles fine.
I realize the knock sensor retards timing, that would be next, but figured I'd throw this up first. Another suspect is it skipped a tooth on the gear/chain, right?


Thanks all

 

[OZNAD]

fuel pump?

 

[martin]

I had the senior mechanic at the local jeep dealer for things like this. He would hook up the RENIX scan tool and figure out what is wrong. Might be worth it to pay an hour or labor to find out.

It could be a variety of things one thing comes to mind is a stopped up Cat converter. I had mine changed out at 135K on my 88 XJ.

You can throw parts at it but might be money ahead to go to a pro. Also ask to talk to the mechanic before he works on it, ask him if he worked as a jeep mechanic in the late 80s. by talking you will know if he the man or not.

I have a guy in huntsville, Al but that too far away from you.

When you changed the TPS did you calibrate it? That is very critical. I also had an ERG go bad, took the dealer guy to figure that out.

 

[5-90]

You say you tested the TPS - did you check function, or just adjustment? You'll need an analogue meter to check function.

Why do I bring this up? Because I had a similar problem with my 88, and it turned out to be flat spots in the TPS response.

Yes, the cat could also be a problem (or some other exhaust restriction - but check the cat first. I don't think the OEM XJ exhaust was double-walled, so crimps are pretty obvious...)

To check TPS function, get an analogue ohmmeter. Disconnect the three-pole TPS connector from the harness, and connect the ohmmeter to two of those terminals (I can't think of which two offhand, but it doesn't matter. As long as the resistance changes when you move the throttle.) Move the throttle blade slowly and evenly while watching the meter, the sweep needle should move slowly and evenly as well. If it jumps, hangs, or skips while you're moving, you need a new TPS.

Do not do this test with a digital ohmmeter - your TPS will fail if you're watching a digital display! This has to do with buffer circuits built into the DMM, and probably won't be your TPS...

Analogue ohmmeters can be had fairly cheaply, just store yours where it won't get knackered about very much (they do, after all, have moving parts.)

 

[MJmk]

I'm wondering what would be related to a noise by the driver's foot? Is this an automatic? Any chance the flexplate has failed and is wobbling around causing the CPS to lose it's signal as rpm increases?? Any strange noises/knocking sounds? Is what I mentioned even possible?

 

[5-90]

I'm wondering what would be related to a noise by the driver's foot? Is this an automatic? Any chance the flexplate has failed and is wobbling around causing the CPS to lose it's signal as rpm increases?? Any strange noises/knocking sounds? Is what I mentioned even possible?

Possible, but the flying height of the CKP nose is relatively low - if the flexplate is "walking" in and out on centre (instead of just flopping back and forth,) it's more likely to just kill the CKP outright than to bung up the signal.

Besides, I've driven with cracked flexplates before - as long as you take it fairly easy on the throttle, it didn't change how the engine ran. Much. (You lost a little performance, and got some noise, but it wasn't anything that couldn't be handled. And, I was able to make freeway speeds until the next paycheque came in a week later to buy a new flexplate and install it.)

 

[jjvande]

what were the symptoms of the cracked flex plate and how did you know to look there?

 

[mud1059]

So I failed to mention it has been to two shops. One was their family friend who couldn't quite put a finger on anything after throwing all the basics at it. I took it to an extremely reputable local shop I knew had a snap on scope. They're also on these forums and have all owned RENIX Jeeps. They were lost as well. Their vote was something electrical

5-90 I only checked it via digital multimeter. I checked everything via this link:
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

Lastly, it has no cat.

Thanks again gents.

 

[lonecountryboy]

Did you check to see if the timing chain skipped a tooth? That would cause those symptoms.

 

[OZNAD]

i think the fuel pump cause i just replaced all the same things that you changed out,same symptoms really, and in the end it was all because of the fuel pump..