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HELP! - Jeep Died!

NHXJer

NAXJA Forum User
Location
Manchester, NH
Hey All:

I need some help here - my Jeep died all will not start!

Saturday morning, I started it up - started just fine with no troubles, and was letting it run for awhile. About 20min in, the Jeep just died. I didn't hear how it happened, I had gone inside for a second to grab something, and it just stopped. It was running fine before that.

I tore into it, and to make a long story short, I don't think the injectors are opening. I have pressure to the rail, but no fuel in the cylinders. It will fire briefly with starting fluid. I tried checking for voltage at one of the injectors while turning it over, and got nothing.

Anyone have any ideas?

Thanks,
Chris
 
Chris,

This would be the time to take you XJ to the dealer or a garage that has the test set for the Renix engine control system used from 1987-1990. Not every garage can test our XJs since they used that engine control for very few years.

I'll give you a little info on the engine control system. The Crankshaft position sensor (CPS), also known as the speed sensor, tells the computer where the engine crank is in the rotation. This information is used by the computer to determine when to fire the spark plug.

There is a sensor in the distributor called the camshaft position sensor. You also hear this sensor called the sync sensor. It is a Hall effect sensor. The sensor is connected to the wire coming out of the side of the distributor. It uses that triangle piece of metal under the rotor to read the camshaft position. This sensor tells the computer the camshaft position, the computer uses that info to fire the injectors. On our XJs our engines shoot injectors in banks of three - like 1, 5 & 3 or 6, 2 & 4.

If you change the CPS you have the options of two versions. The "normal" CPS and the "high altitude." The only difference is where the sensor mounted on the bracket. With the high alt you get more advance which means more power. Since both sensors cost the same at the dealer it is a no brainer. You have a knock sensor to if the engine knocks the timing will be retarded by the computer.

If the sync sensor is bad you have to pull out the distributor. You can either disassemble the distributor and install a new sensor or you can buy a new/rebuilt distributor. I would recommend a replacement distributor. With your age I am sure the bushings are worn. It not smart money to install a new sensor into a distributor with worn bushings.

Once I had a new distributor installed I noticed more power, I already had the high alt CPS installed. The mechanic told me worn bushings can retard your timing.

Now you have some information, you need to have you XJ hooked up to the test set to see if you are getting the signal to the injectors. Call your local garage and ask them if they have the scan tool. I think the snap-on brand one costs $2500, there is not a consumer version you our I can buy :(

HTH

Martin
 
Thanks Martin for all the information!

I swapped the entire distributor from my working 88 today - no dice. I didn't even bother to swap it back - the suspect dist is now happily residing in my "good" Jeep.

I really don't have the money to go get it diagnosed - any other ideas anyone?

TIA,
Chris
 
Sounds like you're getting spark to the plugs if it fires up for a second with starting fluid. So injectors might not be opening... A bit of a challenge without a code reader though.

The C101 connector that some models have can be a source of problems (large connector above brake booster). You could partially pull that apart (maybe 1/4") and reseat it, just to see if that helps. It's full of grease if I understand correctly. Dunno if you want to actually pull it apart or not.

You can also try reseating the CPS connector, just because it's a popular failure.

If you're good with a multimeter you can do a lot of testing...

If you unplug the air temp sensor for example, the sensor itself should have a resistance that varies with temp. At 40 degrees F it should read 7500 ohms, at 70 degrees it's 3400 ohms, at 100 degrees it's 1500 ohms. The same test works for the coolant temp sensor above the driver's side motor mount.

You can test the MAP sensor too. If you unplug it and measure the 2 outside pins of the wiring harness connector (not the sensor itself) with the key in the on position, you should read 5 Volts. Reconnect the sensor. Measure the voltage across the 2 wires farthest from the vacuum port by backprobing them (stab through the insulation with the multimeter probe), that should also be at around 5V with the key on.....
 
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