258 w/Mopar MPI cranks, but not running

[Jsooter]

My CJ7 has been running good for a couple of years (other than misc leaks...). I parked it Friday night with no problems. Saturday, it would crank but not start (occasionally, it would run for a few seconds and then die).

PO installed Mopar MPI.

I check the plugs and they definitely need replacement. I replaced plugs, but that did not help.

It seems to be getting fuel ( I can smell it) and I've verified there is spark. I doubt the timing changed, but I suppose it's possible.

So, any ideas what to check next? Does the MPI kit include a Crankshaft Position Sensor? If so, any ideas where it's located?

Thanks for any suggestions!

 

[hole]

Most of the time the CPS is at the front of the crankshaft, unless the PO went full bore and had the pocket cut into the bell housing. I do not know what the exact spacing(gap) should be, but I've heard it's not uncommon for the bolts coming loose and the unit gets out of adjustment. If you need to replace it you'll have to call Hesco

 

[Jsooter]

Thanks, I'll check that tonight

 

[Torxhead]

I have also heard of that cps getting metal chips stuck on it which would affect its operation as it is a magnet. The cam position sensor located inside the distributor can go bad also, but they seem to last longer than the crank position sensor does.

 

[Hedgehog]

Ohhhh I thought this would be a crank shaft type question. The word "crank" can be so confusing sometimes. But maybe I'm just being a little cranky.

 

[Jsooter]

I found a few small metal chips on the outside of the sensor. I'll remove it to night in order to see if there is any debris directly on the face of the sensor.

 

[Jsooter]

Before I go too far down the path of the Crankshaft Position Sensor, I have a basic operational question: Is possible to have spark and still have a bad Crankshaft Position Sensor?

Thanks!

 

[ThisGuyUKnow]

Before I go too far down the path of the Crankshaft Position Sensor, I have a basic operational question: Is possible to have spark and still have a bad Crankshaft Position Sensor?

Thanks!

Unlikely

 

[ThisGuyUKnow]

Before I go too far down the path of the Crankshaft Position Sensor, I have a basic operational question: Is possible to have spark and still have a bad Crankshaft Position Sensor?

Thanks!

I smell gas is not a good diagnostic tool for ruling out fuel problems, my guess is your pump went bad, the pick up side is kinked or your regulator isn't allowing pressure to hold up. You need to get a fuel pressure gauge and connect it to your Schrader valve and prime the system. If you aren't setting 40 psi and holding for several minutes with the engine off then you have a problem

 

[Jsooter]

I agree- not a good diagnostic tool.

Thanks for the input about the fuel pressure gauge

I smell gas is not a good diagnostic tool for ruling out fuel problems, my guess is your pump went bad, the pick up side is kinked or your regulator isn't allowing pressure to hold up. You need to get a fuel pressure gauge and connect it to your Schrader valve and prime the system. If you aren't setting 40 psi and holding for several minutes with the engine off then you have a problem

 

[hole]

They are relatively inexpensive at Habor Frieght, and some auto part stores have them to loan out

 

[Jsooter]

Measured 0 psi at the rail with key in ON position.

Started tracing things back from the fuel pump and found the relay was not working 100%...connections were very gunked up. Looks like old/dirty dielectric grease or something.

Cleaned the relay and socket with contact cleaner and and then applied a thin coat of dielectric grease.

Now it starts and runs as expected. Pressure at rail is now 50 psi.

Thanks for all of the suggestions and education!

 

[hole]

 

[Hedgehog]

So essentially, when you jump in and crank the engine it cranks as usual even when you crank it up to a higher degree of cranking. I hope you have a tach so it easier to appreciate all the cranking going on. Others have had difficulty with the starter continuing to crank even after the ignition switch is turned off and the engine shouldn't be cranking at all. I had a similar thing happen last year. I jumped in the jeep and it cranked for quite a while before cranking up, but I did notice an unfamiliar rattling so I turned the ignition off and the engine stopped cranking, but oddly enough the thing kept cranking even when the engine wasn't supposed to be cranking anymore. The solenoid was stuck so the starter just kept on cranking even with the engine no longer cranking. In the end with the starter cranking while the engine was cranking the starter destroyed itself. Another $100 gone for no good reason, which of course made me extremely cranky for a time.

Yes, I'm being a cranky old jackass, but I love the English language. Believe it or not I'm not a member of the language police. Within sensible reason I don't mind misspelling, missing or incomplete words, even horrible language skills, but this cranking thing does confuse me from time to time. The word seems to be almost universally used to describe a running engine or trying to start an engine. I think it might be a regional thing. When I was in the service I realized how common speech is different from place to place. For instance how people refer to a soda pop (Coke, Pepsi, Dr. Pepper etc.). For some its a generic Coke, pop, soft drink, soda, soda pop, all correct and common for a given region of the country. We can say things accurately in so many ways and our words can have so many meanings. Honestly, this was a bit of a joke with a purpose. Also, it is great that you found your problem. Diagnosing a problem like this can be highly rewarding.

 

[ThisGuyUKnow]

Measured 0 psi at the rail with key in ON position.

Started tracing things back from the fuel pump and found the relay was not working 100%...connections were very gunked up. Looks like old/dirty dielectric grease or something.

Cleaned the relay and socket with contact cleaner and and then applied a thin coat of dielectric grease.

Now it starts and runs as expected. Pressure at rail is now 50 psi.

Thanks for all of the suggestions and education!

50 psi is too high. The mopar mpi is obd2 and is set to run at 35 to 40 psi.If it is obd2 then it should be 50 psi but that would mean you don't have the mopar mpi kit.

And yes too much psi can be a problem.

 

[Lumpy Grits]

Measured 0 psi at the rail with key in ON position.

Started tracing things back from the fuel pump and found the relay was not working 100%...connections were very gunked up. Looks like old/dirty dielectric grease or something.

Cleaned the relay and socket with contact cleaner and and then applied a thin coat of dielectric grease.

Now it starts and runs as expected. Pressure at rail is now 50 psi.

Thanks for all of the suggestions and education!

Agree that 50 psi is on the high side. I would re-check with a different gauge.
Where did you get the gauge you used?
IMO-You should carry a spare fuel pump(don't go the cheap here)as they are a known issue and will die with out any warning.
THX for the update-
LG

 

[Torxhead]

I would think if the computer picks up that there is that much excessive fuel pressure, it would send a trouble code out.

 

[Jsooter]

I'll double check the pressure tomorrow. Thanks for the heads-up.

I bought the gauge from Amazon: Actron CP7838 Professional Fuel Pressure Tester

 

[hole]

IIRC, if the vacuum line is disconnected from the regulator at the start of the rail it should read 49lbs +/-

 

[ThisGuyUKnow]

50 psi is too high. The mopar mpi is obd2 and is set to run at 35 to 40 psi.If it is obd2 then it should be 50 psi but that would mean you don't have the mopar mpi kit.

And yes too much psi can be a problem.

correction to a typo the mopar MPI kit is obd1. WHich should be 35-40 psi

I would think if the computer picks up that there is that much excessive fuel pressure, it would send a trouble code out.

There is no fuel pressure sensor for the ecm to get such a reading. The way it would detect it is in the o2 sensor if it is detecting too much or too little fuel in the exhaust it can probably adjust the metering to the new parameters but you want to bring the PSI to the correct level for the programming so that it isn't always operating at an extreme.