1989 MJ 4.0 No Spark

[RedBeast]

Well that did it i retarded the distributor a tooth and now it runs just fine. So my when i timed the Cam and Crank i must of messed up tho i double triple and quadruple checked it cause i didn't want to screw it up, i still must of some how.

The resistance in my sensor grounds was some corrosion on my negative battery cable. I didnt get any cables when i got the truck so i stole some off a junkyard 90 something XJ and cleaned them up but inside the hole that the bolt goes thru there was alot of that white sulfur powder, I scrapped it out and now i have only 1.6 ohms of resistance at the MAP, TPS and O2 sensors.

Since i more than likely screwed up the timing chain is there any worry of hitting a valve at high rpms if its retarded a tooth on the cam? Im guessing that power and MPGs will suffer slightly but my worry now is destroying a valve and the head.

 

[8Mud]

The initial timing is going to be the same (or close) if your one tooth off retard. But you are likely to run out of advance quick. I never have been able to get mine to idle right with it one tooth advance. But all XJ's aren't created equal. The cams changed at least once during the model run and some required some fine adjustments to initial setup. Mine idles fine one tooth off, it won't build RPM's. The ECU controls advance (ignition timing) over a pretty broad range, almost enough to be one tooth off in my experience, at least at idle. I've put a distributor in one tooth off on numerous occasions, sometimes by accident sometimes out of curiosity. I never have tried it one tooth off and at full throttle to see what happens.

What's throwing me is the mid range acting up, but upper and lower RPM's working OK. This would be unlikely to happen with a timing or fuel issue. Unless maybe if you full throttle, bypass the ballast resistor and force the ECU into full throttle mode, otherwise you are slowly starving the fuel rail as the RPM's build below full throttle, maybe. Jump the ballast resistor, it's not necessary.

Your issue could be most anything, from CPS, through multiple sensor issues, to some sort of fuel issue. Unlikely to be something in the ignition, ignition problems tend to manifest as poor idle and then show up again at higher RPM's in my experience. I doubt I've seen every possible failure mode in a Renix, if it isn't a probable common failure, it is an improbable exotic failure. I tend to go down the list in order of probability, systematically.

Sorry I have to say this, but thinking 15 ohms of resistance in "a" (likely to be multiple) sensor ground circuits is slightly high, is like saying your fifteen old daughter is a little pregnant. I've had way lower resistance in my sensor ground circuits cause fairly major malfunctions. Just for giggles, test the volts between the TPS ground and the battery negative, the whole ground side of your sensors and even your injectors and ECU may be seriously constipated.

I've tested initial advance with a timing light just to see if it was advancing at all. I've never paid much attention to the actually numbers, as the ECU is changing the advance constantly as the motor warms up, the intake heats up and numerous other inputs. Some guys have said initial advance is around 14 degrees at idle, not set in stone obviously. I've seen Renix idle anywhere from around 450 to almost a thousand RPM's, between 500 and 650 is more typical. Doubtful you'd get the same advance with a 500 RPM idle difference or even a 100 RPM idle difference. Depends on the engine temp., the air temp., RPM, even the barometer and numerous other factors.

 

[8Mud]

Well that did it i retarded the distributor a tooth and now it runs just fine. So my when i timed the Cam and Crank i must of messed up tho i double triple and quadruple checked it cause i didn't want to screw it up, i still must of some how.

The resistance in my sensor grounds was some corrosion on my negative battery cable. I didnt get any cables when i got the truck so i stole some off a junkyard 90 something XJ and cleaned them up but inside the hole that the bolt goes thru there was alot of that white sulfur powder, I scrapped it out and now i have only 1.6 ohms of resistance at the MAP, TPS and O2 sensors.

Since i more than likely screwed up the timing chain is there any worry of hitting a valve at high rpms if its retarded a tooth on the cam? Im guessing that power and MPGs will suffer slightly but my worry now is destroying a valve and the head.

A quick check is to find the number one compression stroke "TDC", then align the timing marks to zero. Take the valve cover off. Rotate the balancer 1/4-1/2 turn to the left and right make sure both of the number one rockers are as high as they go on the valve side with the timing marks aligned. There is likely to be a little play, the timing chain has slack, but if it is far off it will likely be obvious. The exhaust and intake valves are as high as they go at the top of the number one compression stroke with the timing marks aligned "TDC".

If your timing chain isn't misaligned you may want to try indexing your distributor. What this does is find the magic spot to equalize the center point for maximum retard and advance. Usually only an issue on early Renix or sometimes with after market cams.

 

[Ecomike]

I am real curious how they ran this claimed test?

"run to oreilly and finally got around to having my ignition control modules (original and junkyard) checked and they both came up needing to be replaced"

 

[Ecomike]

"Also i have a red power wire in a female spade connector coming off a loom heading to the heater fan motor that has 2 wires orange and green in a 2 prong plug. Where is this red wire supposed to go it has about 15 inchs of wire longer than where the orange and green go into the heater plug connection. I ask because i have no heater fan. it doesnt blow air on any setting."

That red wire may go to a hood light on the hood? It may be missing by now?

Heater fan, called BLOWER on the fuse box, is likely a blown fuse, burned up wire to the ignition switch Connections, and Ignition switch itself..), and to the blower fan speed switch (switch on the dash and connectors) and also likely to be a blower speed bad resistor pack mounted under the dash on the AC/heater core duct work box. All them go bad after this many years.