jlincary

I have a 99 Grand Cherokee Limited with the 4.7L V8. The engine was just rebuilt. The engine starts up fine but as soon as the engine nears 200 degrees on the temp gauge it starts to misfire and eventually completely misfires and backfires. This persists until the engine won't idle and eventually shuts down. I've changed the fan clutch and installed new plugs.

Yesterday I was getting two error codes: P0203 and P1319. After changing the plugs today I was only getting the P1319 code. If I am right, that code is for a bad reading on the cam or crank shaft sensor.

The mechanic that rebuilt the engine thinks the culprit is actually a bad ignition coil that starts acting up as the engine heats up.

Admittedly, dealing with the electrical systems is way over my head.

Does anyone have any ideas on what the cause could be?

Any help is appreciated.

Thanks.

Hymie

My diagnostic program does not recognise P1319, either as a generic or Chrysler specific code.

Interestingly P0203 is Injector Circuit Open Cylinder 3.

In relation to your mechanic believing that the culprit to be a bad ignition coil – this is a classic fault on many vehicles whereby the engine heat, leads to the coil pack overheating and breaking down – giving exactly the symptoms you are experiencing.

No doubt he/she has seen it a number of times during his/her career – but the 4.7L V8 (as with most modern vehicles) does not have a traditional ignition coil. Each spark plug has an ‘ignition coil’ integral to the spark plug connector – such that the spark distribution is done at low voltage. If you inspect the electrical connections to each spark plug, you will see that the individual conductors do not have a thick layer insulation as required by HT leads – although they are routed within flexible plastic ducting.

Therefore you need to consider alternate affects due to something becoming warm/hot. Given that the onboard diagnostics is reporting this as the crank sensor – this it what I would replace and take it from there. It is entirely possible that your problem is due to the crank sensor giving out the wrong signal, once at normal operating temperature.

jlincary

Hymie,

Thanks for the reply. I had a typo on the code. It is P1391 actually. I've done alot since my original post.

I have checked the coils and every sensor I can get to except the crankshaft position sensor and the camshaft position sensor---everything checked out except the MAP. No matter what I tried I just couldn't get any volt readings, not even from the power circuit.

I installed some new components anyway. I have installed spark plugs, TPS, fan clutch (discovered this was bad). and fuel pump and fuel regulator.

My mechanic brought over another mechanic with a diagnostics computer and everything was running great until again the engine got hot and started to stall/misfire. He said all the sensors were giving good readings (including the crankshaft and camshaft position sensors and the MAP).

The mechanic claimed he got a low fuel pressure reading on his computer as the stalling and "misfiring" was starting and was certain the problem was a bad fuel pump. So of course I changed the fuel pump, cleaned the gas tank, and installed a new fuel regulator. We got everything hooked up and we still have the same problem after the engine gets warm.

The engine starts and runs fine until it gets hot. Let it keep running until it was starting to backfire and the check engine light came on. I check the error code on the dash and it spit out the P1391 code. I spoke to my my mechanic and has no clue.

During the removal of the blown engine, could the sensors in question have been damaged. Or, when the rebuilt engine was being re-installed, could the sensors have been damaged or the leads to the crankshaft position sensor have been put close enough to the exhaust that the heat from the exhaust causes problems with the leads (shorting possibly) as the engine heats up?

My next step I suppose is to remove the starter to get at the crankshaft sensor and check the leads for this issue and replace the sensor since I will have it out anyway.

I have read dozens of other posts on similar problems and so far I have not found any certain solutions so any suggestions is appreciated.

By the way, the P1391 code is the only code I got today when the engine started stalling.

Thanks.

tiwvr1

I would replace the crank sensor with a dealer part. Depending on what kind of scanner your mechanic has, it may not tell the whole story. A GOOD scanner will run min of 5k dollars.

jlincary

Any tips for actually getting the sensor out? I have removed the screw that holds it, but I can't get the sensor to come out.

jlincary

Well, I thought I had it fixed. I installed a new crankshaft sensor and it ran great for me for 30 mins or so, but my son just got back from a short trip and it was back doing the same thing.....stalling and misfiring....and we have the dreaded P1391 code again. It also is having trouble starting now.

I also now have the P0340 code in addition to the P1391 code.

Hymie

P1391 is a Chrysler specific code: Interim loss of CMP or CKP.

P0340 is a generic code: Camshaft Position Sensor A – Bank 1 Circuit Malfunction.

Although I would always recommend treating reported on board diagnostic codes with caution – any Jeep mechanic would start by believing what the computer said, and take it from there.

Once you have replaced the reported errant sensors and still have the problem, even an experienced mechanic is likely to be baffled by the problem.

I was interested in the reported low fuel pressure reading, which was not fixed by replacing the pump. Many years ago, on a normally aspirated Ford – I suffered what I was certain was fuel starvation. At the time I had an old clear fuel line connecting the pump to the carburettor, and observed air bubbles (within the fuel line) travelling back towards the fuel tank.

After much investigation, I discovered that the problem was due to a blocked fuel filter in the gas tank, which was causing the problem. Given that fuel starvation would cause the symptoms you have – I would recommend you fully check the fuel lines for any possible restriction/blockage.

My old Ford would often run for 10-20 minutes with no problem, then the blocked filter would create enough vacuum to cause the problem. It could be that the problem occurring when the engine reaches normal operating temperature is a red herring.

jlincary

The camshaft was replaced as part of the engine rebuild. Should the camshaft position sensor have been replaced as well?

This evening after checking voltages on some of the sensors, I disconnected the positive cable on the battery and grounded if for 30 sec to clear all codes. I then drive problem-free for approx 20 miles. There were no reported codes when I shut down the engine.

After having then sat for 30 min or so, my son took the Jeep out on an errand and within 5 mins and probably 2 miles traveled he was back home with the same issues. Codes P0340 and P1391 are up again.

I believe the only difference in his driving from mine was that he had on the radio.

At this point I am giving up and plan to take it to the local Jeep dealership tomorrow.

jlincary

Tonight we changed the cam shaft position sensor and replaced a cracked connector on the negative battery lead. We changed both parts, cleared codes, then tested and it appears we may have solved our problem.

The volt readings on the battery were slightly higher than before so there was some loss apparently due to the cracked connector.

We test drove for approx 30 minutes. Let it sit for about 30 minutes. Then test drove again for approx 30 minutes and we had no repeats of the stalling and backfiring.

So my recommendation for solving the P1391 code is to change the crankshaft and camshaft sensors and make sure your battery connections are in good shape. The sensors are relatively cheap and not very hard to replace.

Thanks to the guys that replied. I hope this is my last problem with this part of the jeep. Now we are on to other things like dealing with a grinding noise coming from the transfer case. I think I already know the solution to that and I don't think I am going to like it.

Hymie

Pleased to hear that it appears you have fixed this problem – hopefully it did not cost too much in false diagnosis to fix. Just goes to show what a nightmare it can be when computer systems (sensors) start playing up on modern vehicles. Although it looks like it took three weeks to sort, it could have taken a main-dealer longer and much more of your money.