Renix issues Update: IT RUNS!

ok, so it still doesn't start when cold without either, but when it does start it purs like a kitten!

Ok, so while reading through my FI manual (about 4 hrs in) we found that the "Sync Signal Generator" otherwise known as a pickup to any non-renix system sends signal to the ECM whether the motor is at #1 or #6, if this signal is not recieved the ecm picks a cylinder and starts its ignition and injection timing.....so we checked and it was out of specs, so in went a new distributor, did nothing, exchanged it as defective, put new one in, changed out to a used ecm, checked to make sure injectors where fireing, install new non-fouled plugs, a little squirt of either and she fires, runs great!

Are there two Coolant temp sensors on this system....the one in the side of the block under the intake (which is the one who sends signal to ecm) seems to be MIA (missing in action), however the guage on the dash seems to be working properly.

This jeep has not run properly since I purchased it, it feels like a great milestone that it does now....however still very frustrating that it won't start when cold.

My next step is to go through and try to find the MIA coolant temp sensor in block and go through and try to figure out why it won't start.

Thanks to all who have helped out so far, but, any sugestions as to starting when cold would be greatly appriciated!

Thanks,
Justin Ray

I have a 88 XJ and tired to change the engine temp sensor you are talking about. It is located behind the motor mount bracket on the driver's side. After I rounded off the corners I took it to the dealer and had the mechanic pull it out.

You are right the temp sensor in the heat ONLY provides information to the instrument cluster. The sensor on the driver's side of the block provides the computer with data.

If you were closer I'd be more than glad to hook up my snap on MT2500 scan tool and read the engine computer and see what sensors are in and out of spec.

In the past 3 or so years I replaced EVERY sensor which controls the engine operaiton. The engine ran better every time I changed a sensor.

It is hard to fix a vehicle by guess work. The taking the vehicle to the dealer or to a garage you trust and paying them 1.0 hour of labor to run a diagnostic on it would be of great benefit. They will make sure your TPS is in calibration along with making sure the injectors are firing and the pulse width.

The sensors which determine the fuel/air ratio are:
* Inlet air temp sensor - located in the intake manifold
* Manifold ABS pressure (MAP) Sensor - mounted on firewall with hose to the throttle body
* Coolant temp sensor

Spark and fuel
* Crankshaft position sensor (CPS) - mounted on bell housing, if you buy at the dealer you can get a high alt which gives your more advance
* Camshaft position sensor, also called the sync sensor. Located in the distributor. To make sure I got mine replaced i purchased a "new" not rebuilt distributor at the dealer.
* throttle position sensor (TPS) - this part needs calibaration.

The knock sensor will retard your timing if it detect pinging. It also located by the eng temp sensor but has a connector like a fuel injector.

I recommend you replace these over a years time. I buy one sensor every time I got paid. For starters I'd replace the 3 sensors i have listed under fuel/air if you are using the guess method. Replace them due to age if nothing else, forget testing to see if they are good.

So far all other sensors check out within specs according to the information I've found. Of course without the diagnostic tool or an ossilliscope the only thing you can check on a CPS is the resistance value, which mine checks to be within specs of 200 +/- 75 ohms, a new one on the shelf check out at 236 ohms, mine on vehicle checks at 216 ohms....so I *think* its ok.

The TPS is adjusted to proper specs acording to the manual....its simply a potientiometer that varies the input voltage from the ECM on the output, it tests within factory specs and is adjusted accordingly.

The sync (or pickup) was replaced, mine tested out of spec, but with continuity all the way to the ecm and ground, so I replaced it. The second distributor I got actually worked, when turning it you could actually feel the resistance as the the distributor would pass by the #1 and #6 positions, also the air gap seemed much better set than the first.

The MAP sensor also checks out within spec at both idle and WOT.

I have not checked the inlet air temp sensor and as stated the coolant temp is MIA, I've got one coming tomarrow, I just have to make sure the factory wires and plug is still there.

Thanks for the input, hopefully I'll get this thing worked out soon.

Justin

The "static" testing of sensors tell you it good for that one point, those tests do NOT tell you if the sensor works properly in a "dynamic" situation.

With the age of the vehicle replacing the sensors I mentioned is just routine maintenance.

I have learned the hard way the mulitmeter method of setting the TPS does good enough to get the engine running. I set mine that way and then took it into the dealer for a problem. The mechanic told me my TPS was out of spec and he set it for me in addition to the other repair he did.

I also helped two buddies with their late 80s GM vehicles with TPS that require calibration. They both set their new TPS using the multimeter method and when I hooked up my snap on scanner found they were .2 volts too low - the buick was .2 and should be .4 volts, the Vette was .4 and should have been .6 volts. The problem with the mulitmeter method is that it does not take in account the voltage drop in the wire from "the TPS to the computer". You will always have a low value. Your TPS may of been set right before your adjusted it.

I also recommend you start replacing sensors because they stopped selling engines with that engine control in 1990. Part are beginning to disappear for those AMC items not used by Chrysler on the post 1990 XJs. I think the TPS is a 100K mile item, along with all those other sensors.

Not sure how long you owned the XJ but there does come a day you have to replace parts, get use to it as an owner of an older XJ.

guess I forgot to mention that the previous owners couldn't figure out why it wasn't running or starting right, so they threw alot of parts at it like: new TPS, new Idle air stepper motor, new coil, new computer, new alternator, new starter, new electric fans...not to mention all the money they put into the suspension and tires only to sell it for a fraction of what they spent.... all because they couldn't make it run right

thanks for the insight....I didn't even think about the static vs. dynamic testing....a local shop with the correct tester said they'd run it for $30 so, I guess when I get it running I'll take it overthere and have them check it for me....said I could be there for testing to see what was going on.

I'll let yall know when I get the coolant temp sensor on and test the intake temp sensor.

Justin