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1994 B350 5.9L V8, runs rough and pops
02-18-2010, 10:10 PM
Hi, I'm at my wits ends trying to diagnose, let alone fix this mess. The van is a fried of mine and has around 200,000 miles, before it got to me it had 2 rebuilt computers put in and the trans rebuilt (don't ask my why they thought that would help. Anyway, here's the issue, it starts great, has 39lbs of fuel pressure, new cap and rotor and plugs and wires and a used distributor (just to check), and no cats, but shortly after it starts, it begins to idle roughly and engine shakes, and begins to load up. Under load it'll sometimes run ok, mostly backfires through the throttle body and out the exhaust. We tried unplugging and pluggin the 60 pin for the computer a few times, cleaned the grounds. The only code that comes up is 27. All the injectors ohm out ok, and when hooked up, all the noid lites blink. I removed the fuel rail and actually watched the spray pattern and they're all a nice fine mist. The only think I can think of now is a camshaft or valve issue. Anyone have any other ideas?
02-19-2010, 12:46 AM
The only code that comes up is 27. All the injectors ohm out ok, and when hooked up, all the noid lites blink.
It sounds to me like you have a wiring harness issue, probably intermittent connection at the PCM connector. Try spraying the prongs of the connector with electrical switch cleaner and then connecting/disconnecting it several times.
What's a "noid light"?
02-19-2010, 11:14 AM
Thanks for replying. I did unplug and re-plug the 60 pin connector and spray it many times, to no avail. I heard that was a trouble spot, but i can't find anything wrong with it.
A noid light is a light that plugs in place of an injector and lights was the computer fires the injector. handy tool.
02-19-2010, 01:10 PM
Okay, then next considering it has 200K on the clock, I'd have to go with worn timing chain that possibly skipped a tooth. This would result in both the valve and ignition timing being slightly retarded. That in turn would explain the backfiring.
02-19-2010, 01:13 PM
I agree on the timing chain and that's what I thought, so when my firend was checking it with his mt2500 he said the cam sensor and crank sensor were good with eachother, which i suppose means the chain can't have jumped. If it wasn't so tight up there, i'd just take off the cover and look, but that's a job in itself.
02-19-2010, 03:39 PM
he said the cam sensor and crank sensor were good with each other, which i suppose means the chain can't have jumped.
Unless someone rotated the distributor at some point to put them back in sync.
02-19-2010, 05:50 PM
Possible, but someone told me that distributor timing in this example only affects the injector pulses, not actually cam timing. I didn't think that made any sense, but I didn't have enough information to call him on it.
02-20-2010, 04:20 AM
have you scanned all the sensors, I would also perform a compression test just to make sure
02-20-2010, 02:10 PM
someone told me that distributor timing in this example only affects the injector pulses, not actually cam timing.
They are correct, the cam timing is tied to the crankshaft by the timing chain. Rotating the distributor adjusts the injector pulse to sync it with the crank. So even if the cam timing is off, the injector pulse could still be correctly synced with the crank. Backfiring through either the exhaust or intake only happens when the spark plug fires and one of the valves is still open.
02-20-2010, 03:50 PM
just check the timing chain. make a mark on the crank damper on the tdc mark on the front timing chain cover, remove the distributor cap. turn the crank until the distributor rotor moves and inspect how much the crank damper moved and let us now how much it turned, if its the timing chain you'll know..
02-20-2010, 04:50 PM
The slack test is actually a bit more involved. This really should be done with two people, one to turn the crank and mark it, the other to watch for distributor rotor movement.
There is a very simple check for a loose timing chain due to a broken tensioner, worn gears, or a stretched chain. Pull the distributor cap and observe the rotor position. Take a breaker bar and a appropriate socket and put it on the crankshaft damper pulley. If you have a degree wheel put it on the damper pulley else you can just chalk mark the timing mark position at the appropriate time.
Now - slowly turn the crankshaft pulley in a clockwise direction. Watch the distributor and observe that the rotor is moving. Stop turning. Now - mark the damper pulley position with the chalk or observe the degree wheel. Very carefully turn the crankshaft in the other direction and VERY carefully observe the rotor in the distributor. The instant it begins to move STOP turning and mark the crankshaft position again. Measure the number of degrees of rotation of the crankshaft. If there is a lot of slop in the chain then you will have moved the crankshaft ten or fifteen degrees (or more) before taking the slop out of the chain after the reversal before the camshaft began to turn. Get the picture?? If all is well and there is no slack in the timing chain then you will see about three to five degrees of "reverse motion" before the distributor begins to turn.
If you are not sure how many degrees it turned during the procedure there is a simple way to calculate that based on the spacing between the chalk marks. Take a string and wrap it around the crankshaft damper where you made the chalk marks to measure the circumference of the damper. Let's say it was 18 inches. If there is one inch between the chalk marks then divide 1 by 18 and multiply the result by 360 (the number of degrees in a circle). In this case the answer is 20 degrees and it is time to replace the chain/gears!!!
02-22-2010, 12:05 AM
Had a chance to check compression. 7 cylinders at 130, one at 150. Not perfect, but plenty good enough. I haven't had a chance to check the chain slop yet, will get to it as soon as i can. Thanks to everyone for their comments and help, it's very much appreciated.
03-01-2010, 11:48 PM
Finally had some time for the van. Checking timing chain slop, while timing the distributor, very minimal, I was quite surprised. Tried a temperature sensor, no luck. Tried a map sensor, no luck. Timed distributor, improved the idle quality when cold. So, here's an update on the issues. Starts and runs great when cold. As soon as the temp starts to climb, it pops out the exhaust and lopes very badly at idle. Fresh tuneup, new fuel pump, injectors all tested, hundreds of new sensors. Fresh out of ideas.
03-02-2010, 12:27 AM
whats the fuel trims and 02 sensors readings when it's running rough?? does this year have an egr valve
03-02-2010, 08:35 AM
It's got an egr valve, which we took off, cleaned, checked the best we could and reinstalled, no change. I'm not sure on the fuel trims, i only have a code reader, but a friend who scanned it with his mt2500 said everything checked out good. I could probably con him into coming back out and checking it again if you think there's a need.
03-02-2010, 09:27 AM
As soon as the temp starts to climb, it pops out the exhaust and lopes very badly at idle.
hundreds of new sensors.
Does that include a new 2-wire coolant temperature sensor? (Not the 1-wire one for the gauge.)
03-02-2010, 11:21 AM
Yep, that's the temp sensor we replaced, with no change. Does anyone have the Mopar instructions for timing the distributor? The instructions i have say to position the distributor as close to the switching point as possible, but if you are turning the dist., it switches from 0 to 5v at one point, then if you turn it back the other way, it switches from 5v to 0 at a different point. I set it exactly in the middle of the 2 switching points. Is that correct?
03-06-2010, 12:35 AM
try block off the egr. if you thinks it's timing just start the vehicle loosen the bolt a little and turn it slowy until it runs fine, what does the plugs look like
03-06-2010, 12:41 AM
what happened to the code 27 have you checked that. have you also checked for a plenum manifold vacuum leak??
03-06-2010, 11:20 AM
Brought the mt2500 back out and found that the crank sensor was bad. Changed it out and it's back to good. Looked it it first, but you could tell that it had been out of there and the owner said it had been replaced. Too bad it didn't show up earlier, woulda saved a lot of dickin' around. thanks for all the help everybody.
03-06-2010, 12:58 PM
found that the crank sensor was bad.
One thing that irritates me about OBD-II is that there is no crank sensor checking or trouble code. That's a major oversight IMO.
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