94 5.2L Magnum running rough

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dartslantsix

dartslantsix

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My Barracuda has a 94 magnum swapped in from a Grand Cherokee. Stock injection.
After sitting through the winter, I started it and it's running really rough. It smells like it's running rich. It tries to idle down, almost dies, then idles back up. When I rev it up, it smooths out some, but not as smooth as it should.
Here's what I've checked so far:
No codes from the PCM.
Inspected all ignition stuff: Cap and rotor look good, plug wires checked out, plugs look good except #4 was wet with fuel.
While running, I pulled the idle air motor connector and nothing changed. Pulled #4 injector wiring, no change. Pulled the vacuum line to the fuel pressure regulator and it also didn't change anything.
My next thought was that #4 injector was leaking. Pulled the rails and pressurized the system, no leaks from any injectors. I ran the pump for quite a while and pulsed a few of the injectors with jumpers. They spray fine, nothing weird.

I'm stumped. My next step will be verifying fuel pressure. Other than that, it could be coolant temp sensor?

What else should I check?

Thanks.
-Dave
 
Did it sit with ethanol gas in it?
 
My '94 Ram did that. Coolant temp sensor (there are two) was reading 14 degrees when it was 70 out, at first startup. The closed-loop kept the symptoms at bay until it was warmed up, driven, and open-looped itself into drowning in fuel. (I think it used one coolant sensor for the closed loop, and one for open). It was dumping fuel because it thought it was cold.

It won't throw codes, and it will need new spark plugs if that's it. I had to use a Snap-on scan tool (Thanks, Chris!) to see what the sensor outputs were, exactly.

New sensor fixed the issues immediately.
 
You may have just 1 bad spark plug, (Or wire) if you checked all those other things & they checked OK. jos51700 is correct about the coolant temp sensors too, (Up until 96, that's when Chrysler went to OBD2) but 1 (with the single wire connector) is for the temp gauge & the other one (2 wire connector) is for the computer & that may be bad, causing a problem. My first guess, try a fresh plug in #4. That's probably all it is.
 
Pull the plug wire off #4 when running if no change its that cylinder. Kind of sounds like it.
 
check compression ?? might be a stuck valve?
 
Thanks for the ideas, guys.
I'll check the temp sensor with my multi-meter to see if it's in spec.
Probably also check the inlet air temp sensor.
If that checks out, I'll compression check the cylinder.
If that checks out, I'll throw a new plug in #4.

Not sure when I can get back into it, but I'll update when I do.
 
Ok, update on this:
Checked compression. All cylinders are 170 psi except one was 165 and another was 180, so that seems good.
Manifold air temp sensor was out of range, replaced it.
Coolant temp sensor was out of range, replaced it.
Plugs are black from running rich, so I cleaned them with emery cloth and re-gapped them.

Car still runs rough.

Do I need to replace the plugs or is cleaning good enough?

Still need to check fuel pressure.
 
I would surely replace the plugs anyway. Good old Autolite 3924s work fine in these engines so there is no need to use expensive ones. It is possible one of the plugs has cracked porcelain/insulator from removal & installation. A spark plug socket should be used on these, it prevents this from happening. If you don't have one, get one. I believe it is a 5/8'' socket. Bad plug or plugs is more than likely what is wrong. Fuel pressure should be right around 45PSI at the fuel rail on a Magnum engine.
 
Does it run OK if you give it moderate throttle?

IAS solenoid is a known wear item about this age. If you still have the OEM injection- back of the throttle body.

Causes extremely rough idle or stalling at idle but part throttle makes it run good or at least stay running.

$20 part and 15 min labor.
 
Today's update:
New plugs, no change.
Just checked fuel pressure: 34-36psi the rough idle made the needle move, 44 psi with vacuum removed.
Service manual says: 31 psi at idle and 39 psi with vacuum removed.

So I'm about 5 psi higher than the book says. Is that enough of a difference to make it run bad?
 
Does it smooth out if you give it moderate throttle?
 
dartslantsix said:
Today's update:
New plugs, no change.
Just checked fuel pressure: 34-36psi the rough idle made the needle move, 44 psi with vacuum removed.
Service manual says: 31 psi at idle and 39 psi with vacuum removed.

So I'm about 5 psi higher than the book says. Is that enough of a difference to make it run bad?
Click to expand...
My 95 Dakota with a factory 5.2 Magnum was 45psi at the injector rail port & that was from the factory service manual. I had no vacuum operated fuel pressure regulator on the engine, the in-tank pump regulated the pressure. I don't think your fuel pressure is low enough or too high to cause a rough idle. Next step I would do is check for a vacuum leak somewhere.
 
Does it smooth out if you give it moderate throttle?
Click to expand...
No, it runs rough off idle too.

Friend came over and threw a timing light on it and we noticed that the light would skip a flash occasionally. Then the engine just completely died a few times. He said the light shut off when the engine shut down. So we knew it was somewhere in the ignition. First I tried a spare crank sensor. (this was a used sensor that I can't verify is good, pulled it in the fall trying to chase down another problem) The car then ran smooth, but would shut down after a few minutes.
Then I tried jumping the ASD relay and the engine ran great. Put a new relay in and the engine is still randomly shutting down.

I'm starting to wonder if I have two bad crank sensors, but each one fails in a different way. In the fall, the car would randomly shut down. I replaced the crank sensor then and didn't have any issues until this one. But I didn't drive it because it was winter.

This is a tough one.
 
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What about the pickup in the distributor? Just an idea.

Pretty sure you are aware, but just in case, there is a difference between an auto CPS and a manual one. The auto one is longer and can (will?) rub on the flywheel. The plug is keyed differently so shouldn’t be an issue. Sticks in my head that you talked about that in your blog though.
 
Either way, the CPS sounds like the source of your problem if it changed the way it ran.
 
DionR said:
What about the pickup in the distributor? Just an idea.

Pretty sure you are aware, but just in case, there is a difference between an auto CPS and a manual one. The auto one is longer and can (will?) rub on the flywheel. The plug is keyed differently so shouldn’t be an issue. Sticks in my head that you talked about that in your blog though.
Click to expand...
Dion, yeah I know about the different crank sensors auto/manual. I had to swap connectors in the harness to run the correct sensor.
My understanding is the pickup in the distributor times the fuel injection, correct?

I agree on the crank sensor.

Sidenote: We just picked up a hemi to swap in after this summer and my wife is saying that this is a sign to just rip the current motor out. Problem is I want to make sure this engine is good before selling it to a friend. And I'd like to do some racing/cruising this summer.

-Dave
 
You have a crank sensor in the bell housing behind the right head, and a cam position sensor in the distributor. I would check that. I believe the cam position sensor generates the pulse for both the timing and the injector pulses, the crank sensor tells the CPU which cylinder is at TDC since it's sequential injection and not batch fire. A bad MAP sensor (or the little rubber elbow) can also cause a too rich condition that might foul out a plug. Does it use oil? The "keg" intakes have a bottom plate which develops a leak over time and causes a vacuum leak into the lifter valley. The injection system can only compensate for just so much. Cheap fix, but a PITA to pull the intake.
 
dartslantsix said:
Dion, yeah I know about the different crank sensors auto/manual. I had to swap connectors in the harness to run the correct sensor.
Click to expand...

I thought you had but couldn't remember for sure. So thought I would mention it just in case.

dartslantsix said:
My understanding is the pickup in the distributor times the fuel injection, correct?
Click to expand...

I think the distributor just tells the computer where it is in the cycle. It might know #1 is at the top, but is it at the top of the exhaust stroke or the compression stroke? Which probably means it wouldn't cause rough running and might be more of an "on/off" issue where it either runs or it doesn't.

dartslantsix said:
Sidenote: We just picked up a hemi to swap in after this summer and my wife is saying that this is a sign to just rip the current motor out. Problem is I want to make sure this engine is good before selling it to a friend. And I'd like to do some racing/cruising this summer.
Click to expand...

Nice! What year? What are your plans for mounts and such?

I understand the idea of wanting to keep it mobile during he summer. I too have acquired a G3 but don't have it ready to go in so it will wait until (hopefully) this winter before I do the swap along with the T56 I have. At the same time, I am just itching to get started and it is hard to push pause.
 
dartslantsix said:
My Barracuda has a 94 magnum swapped in from a Grand Cherokee. Stock injection.
After sitting through the winter, I started it and it's running really rough. It smells like it's running rich. It tries to idle down, almost dies, then idles back up. When I rev it up, it smooths out some, but not as smooth as it should.
Here's what I've checked so far:
No codes from the PCM.
Inspected all ignition stuff: Cap and rotor look good, plug wires checked out, plugs look good except #4 was wet with fuel.
While running, I pulled the idle air motor connector and nothing changed. Pulled #4 injector wiring, no change. Pulled the vacuum line to the fuel pressure regulator and it also didn't change anything.
My next thought was that #4 injector was leaking. Pulled the rails and pressurized the system, no leaks from any injectors. I ran the pump for quite a while and pulsed a few of the injectors with jumpers. They spray fine, nothing weird.

I'm stumped. My next step will be verifying fuel pressure. Other than that, it could be coolant temp sensor?

What else should I check?

Thanks.
-Dave
Click to expand...
I would also clean the iac.
Also clean the throttle body iac port.
 
I have a 94 Magnum in my Dart, also running factory EFI. You might be on to something with that crank sensor for the issue of it just shutting down.

For the rough running, you might just have a clogged injector. You can have them professionally cleaned, or you can get one of these things from the jungle website and feed some good old carb cleaner through them yourself. That's what I did, and while my engine didn't seem to run any better I can say for sure that the injector spray patterns were better:
Amazon product ASIN B0126MEK3C
The other thing I'll say is that your fuel pressure is a bit low. The factory service manual for a 94 Dodge truck says this about fuel pressure:

1685718747065.png


I'm using a filter / regulator from a 2002 Jeep, which makes my fuel pressure about 52 psi, and I don't have issues with it. I'm thinking with your low-ish fuel pressure a clogged injector or two might show up much more readily and cause it to run rough.
 
My EFI training is pretty basic, but one thing I know;
OOPs my computer lost power, I'll have to reboot, be back in a sec. Ok so the programming is not letting me cut and paste so, Go to the bottom and read Note-1, then come back to the top and begin reading at Page-1

Page-1
Again, My EFI training is very basic. I'm only responding cuz this thread is on like page 15.... Ok then;
My understanding of the sequential EFI System, is like this;
The ECU, during cranking, looks to the CPS to know that the engine is cranking, and when it gets to #1; then looks to the Cam sensor to figure out on what stroke #1 is at (compression or exhaust). I believe this is called establishing synchronicity.
Once it knows that, it begins counting (18436572) from the cam-sensor signal, and never looks at the CPS again until the next restart.

It seems to me that your ECU is momentarily losing the cam signal, and forgets where it was in the counting. When that happens, I bet the ECU has no choice but to start over, and to look to the CrankPS to re-establish synchronicity.
Since the engine is spinning and has not yet stalled, it figures out where it is and starts running again. The ECU only needs a MAXIMUM of two crank revolutions to do this.
But since the engine does occasionally stall, I'm guessing there are times that it is not getting the Crank signal either!...... This would be highly unusual. More likely is that the issue is in the Power supply or the wiring, or the computer.
or the coil is going bad.

A failing coil will show up, in Closed Loop, as running rich whenever it missfires. But so will a bad injector. AND it is theO2 sensor that is fiddling with the AFR to compensate. To figure out which it is, you gotta fool the ECU into not recognizing the problem, so then, put her back into Open-Loop, which will cause the ECU to go back to it's base-programming, which is running off the CTS. This will put the O2 offline so you can actually do some diagnostics.
So now, in Open-Loop, with the CTS running the show, if nothing else, at least the O2 won't be modifying the fueling.
The base programming is really pretty good.
At this time, I would also unplug the AIS, so the Idle speed remains stable.
So now, the engine should be idling without any interference from the O2 nor any changes in rpm. Therefore, if the rpm is changing, it can only be caused by:
1) changes in ignition timing or
2) by flooding if an injector is bad. or
3) by an intermittent vacuum leak .
As to #1, the timing lite will tell the tale
As to #2, the stink out the tail pipe should clue you in
As to #3, I've never heard of that, lol.

Note-1
If the engine has an original beer-keg intake, of course the first thing to do is prove that the clean-out plate is not sucking up CC blow-by, which they are famous for doing. Proving this is pretty simple ; just flip the PCV out of the cover grommet, seal both valve covers and put a vacuum gauge on the dipstick tube, then start her up. Set up like this, the CC should immediately start building pressure, and if it does, shut it off before the pressure exceeds 3>4psi. But if the gauge reads vacuum, then the intake has got to come off and the clean-out plate resealed; then start over.
 
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Thanks @AJ/FormS , that's some good tech.

To follow up: I replaced the crank sensor just now and it's running fine again. Didn't get a chance to drive it yet due to graduation parties (and a 2010 Charger parts car clogging the drive way).
It idles good and the exhaust isn't stinky either. Let it warm up fully and it seems good. That's two bad crank sensors... they seem to last about a year and then POOF!

Thanks for everybody's help.

-Dave
 
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