Magnum swap starts, does not run

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dartslantsix

dartslantsix

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Okay, so I tried starting my car today for the first time. It starts, runs for a couple seconds then dies. The amount of time it "runs" is not consistent. Working the gas pedal doesn't seem to have any effect.

I have good fuel pressure at the rail- with key on it is 12-14 PSI and it climbs for the short time that the motor is running.

I double checked that we have the spark plug wires routed correctly. Distributor was never removed, so it should be fine.

This is the set up:
Out of a 1994 Jeep Grand Cherokee (OBD I). Ran great in the Jeep. Using the Jeep relay/fuse box. Everything is stock for the Jeep. I have removed all the EGR and Evap equipment.
Neutral safety is grounded at the computer. I have one wire hot to the computer all the time, one wire hot on key on.
I tried to check codes using the CEL wire off the PCM, but it doesn't light my test light and my voltmeter doesn't move enough to discern how many times it's flashing.
I had heard that the ignition switch has a dead spot between start and run that the PCM does not like, so I wired in a start button so it would not cause an issue.
Jeep had an auto, I swapped in a 5-speed. I put in the correct V8 flywheel and had to change the crank sensor to a manual shift sensor. The two sensors had differing wiring connectors, so I swapped the connectors. Not sure if this may be incorrect.

Not sure what else to look at. I've heard that the Jeep's have a security feature that needs to be disabled. I'm going to start searching for that, but does anyone have anything I should look at first?

Any help is greatly appreciated.

-Dave
 
hey dave, another dave here. I did mine with a 5.2 mag. from a 01 ram, but it was obd2. not real sporty on the obd 1. I do know that it needs around 30-33lbs of pressure at the rails at start up. also, on mine, I had to hook the start and key on wire together for the switched power wire. I know the security set up will let it start and run for a few seconds then die. it will do this 5 or 6 times then it wont start at all. again this is on the obd2 system. yours may not have this being a 94. there's several here that's done the earlier system, and I'm sure they will chime in. be glad to help if I can. dave.
 
Thanks for the input so far. I tried jumping the Auto Shutoff Relay, that didn't seem to affect it. Tried starting this evening and it's trying to run longer. It's acting like it's missing- it's making me wonder if the injectors are sticking on some of the cylinders. I'll let it sit tonight and try tomorrow. I'll pull the plugs too to see if that shows anything.
 
So it starts and runs for a few moments , then shuts down. I'm not too up to speed on your particular set up. That said, there should be a crank sensor at the flywheel housing, I would check and verify it's generating a pulse to the control unit. I believe that is what is used for establishing #1TDC . If it can't establish #1 , it might not be able to tell which injector to "fire" and for how long. Just something to ponder.
 
Okay, did some more poking around today. Pulled all the plugs. Each plug smelled of gas.
I then checked for spark at each plug and this is where it was weird. I had spark, but not a consistent bright spark. It would alternate between bright and dim spark randomly. Not sure what controls the strength of the spark other than the coil.

Any ideas on what I should check next?

Non consistent spark would definitely cause what I was seeing yesterday.

Thanks.
 
Couple things to peek at. For starters, condition of cap and rotor. Ever been touched? Spark towers and rotor tip chalked up? Magnetic pickup breaking down? The gap between stator and reluctor inconsistent? How about the plug from the pickup? Tight, clean , no unwanted power or ground shorts? Just a few things more to look at.
 
I'm pretty sure the magnums that year should have 45-52psi in the rail before startup, 12-14 I'm surprised it's starting at all. Try getting a can of carb cleaner and keep it running on that, it will at least narrow down between fuel and spark. Just to make sure, your rail shouldn't have a regulator on it being a 94, but 92-93 does (I think?). Just picturing your setup, my 68 fury is 94 obd1 5.2, so probably very similar.
 
I agree with Dave and Ralphie on the fuel pressure - way too low. I have a spare 92 5.2 fuel setup and it does have the regulator on the fuel rail with the return line to the tank. You need to eliminate the fuel pressure situation first, then move on.
 
ralphie361 said:
I'm pretty sure the magnums that year should have 45-52psi in the rail before startup, 12-14 I'm surprised it's starting at all. Try getting a can of carb cleaner and keep it running on that, it will at least narrow down between fuel and spark. Just to make sure, your rail shouldn't have a regulator on it being a 94, but 92-93 does (I think?). Just picturing your setup, my 68 fury is 94 obd1 5.2, so probably very similar.
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ok, my bad, I thought the higher pressure came in with the obd2. i do know 12-14 wont cut it. it needs to see at least 45 as soon as you hit the key. dave.
 
I was thinking that the Magnums with the fuel regulator on the rail was around 35 psi. I know the injectors are different. That's one reason I didn't interchange the rails on mine in order to use the regulator. I only had 7 of the older injectors.
 
From what I gather all 360s and most OBD-IIs have the high pressure. Early motors have the 35psi- but that doesn't mean they all do.

As for security, if anything came with security in '94 that donor'd be it. Can't say they did and that'd be the problem even though that's similar. Definitely need to figure out when you've got half/a third the pressure you need. If everything came from the Jeep but the sensor/flywheel- are the injectors still the same? What pump do you have, and what's the rest of the fuel system like?
 
Thanks again for the input. I've had some time here and there to check some things. First, let me clarify what the engine is doing.

It's not actually starting all the way. It catches enough that you think it's starting so you let go of the starter and then the engine chugs along for a while before dying. Sounds like only a couple cylinders are firing.

This set up has the fuel regulator on the rail itself. I rechecked pressure. With key on, it goes to about 12 PSI and bleeds off. During start, pressure goes up to 45 and stays there until the engine stops "running".

We re-checked all the grounds and they are tight. Spark from coil wire to ground is good. Spark appears good at the plugs.

Last night I checked one of the injectors and it is pulsing during start. Didn't check the rest since I didn't have time.

At this point I'm wondering if it's in time. Engine ran when pulled and distributor wasn't messed with. Cap, rotor, wires and plugs are new. Firing order was triple checked.

I'm wondering if the automatic's tone ring is clocked differently from the manual trans flywheel I'm using. If that was the case, the computer could not sense the correct timing. I've heard some guys say a manual trans PCM is required, others say the Auto PCM works fine. Called B&G Performance today (who reflashes the PCMs) and he said a manual trans PCM is required.

I might be able to put a timing light on it tomorrow.
 
When I first did my manual trans magnum swap in my Dakota, I had an auto PCM in it, it ran fine but threw auto trans codes, so I don't think that is your problem, but not sure. Also double check the PCM pinout and make sure there isn't a 12v ign source missing. It almost sounds like an old ballast resistor issue where it would run in crank but die in run?
 
Okay, here's how I've done the PCM wiring.

Battery, cavity 3 red wire is hot all the time.
Ignition Acc feed, cavity 9, light blue is hot when the key is on.
All the wires listed as ground are grounded. Except "sensor grounds" which go to the sensors.
All the cavities with plus marks next to them I cut out.


pin%252520out.JPG
 
I think that you have hooked up everything correctly as far as I can tell, I looked at a schematic and it looks fine. The only wiring thing I would check is how/when pin 9 is getting power. The original ignition switches have 2 ign positions, and they are separate terminals. In start, the coil got full 12v, so there is a (brown?) wire for ignition in start, and then a (blue?) wire for ignition in run. What I did was connect those two wires together coming from the ignition switch, and then hook them to the pcm. This way the pcm has constant 12v in run and start. You could temporarily hook pin 9 up to 12v battery and try it to see if its dropping out. Sorry if you checked all this, everyones setup is a little different!
 

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The only wiring thing I would check is how/when pin 9 is getting power.
Click to expand...

Just checked this with a multimeter. Was using a test light.
Pin 3 is 12V constant.
Pin 9 is 12V when key is on.
Numbers dip slightly when the starter is activated, as expected.

This weekend I'll check some other things in more depth. Thanks again.
 
Good luck this weekend. Geez, it feels good when it fires up!!
 
It lives! Turned out to be crank sensor wiring. It's still not 100%, but it idled for 10 minutes and now I can check codes tomorrow.

When I swapped the connector for the crank sensor, I thought I had everything right, but obviously not. We just started swapping the wires around until it fired. I'll check my notes in the morning and post what wires go where on the sensor.

The previous wiring must have given the PCM just enough signal to fire, but not in the correct timing.
 
Good deal! You're going to love driving it, my fury is such a fun car!
 
Well, that didn't last long. It's back to doing the same thing.
I had swapped some wires around on the crank sensor to see if that was the issue. When I did this, the fuel pump would not even run. With the sensor disconnected then the pump ran with key on. So we tried a few more combinations of the wiring until we hit the one that let it run last night. It still sounded like it was missing on a few cylinders, but it was running.

I checked the wiring this morning to post up what worked and to my surprise, it was the same setup that I started with way back when I started this thread. Uh, what?

A friend of mine did this swap in a Jeep and said he had trouble with air in the fuel rail, so this afternoon I jumped the fuel pump relay and ran some gas out of the schrader valve to see if there was air. A few bubbles came out. Then I tried firing the car and it's back to running for a bit then chugging and dying.

I'm wondering now if the injectors may be clogged. This motor sat for about 2 years with the fuel line disconnected. A few months back I pulled the fuel regulator and it had some sandy dust stuff inside. I cleaned it out, but some of that could be clogging the injectors. Probably won't hurt to pull them and clean them out.

We were able to pull some codes out of the PCM this afternoon.
34= cruise control
53= PCM fault, I believe this is due to the computer not being able to communicate with the trans computer
72= Cat circuit
55= end of codes

Any other ideas?
 
sounds like mine when the cam sensor was out of time. you sure the distributer wasn't moved? you don't have to take it out to mess it up, just rotating it will throw it off.
 
aaadave said:
sounds like mine when the cam sensor was out of time. you sure the distributer wasn't moved? you don't have to take it out to mess it up, just rotating it will throw it off.
Click to expand...

I took my distributor out. How do you fix that - if it turns out to be a problem?
 
68coupe said:
I took my distributor out. How do you fix that - if it turns out to be a problem?
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It's called distributor sync with the drb. Or with the engine at tsc and the ign on, backprobe the cam sensor wires with a meter. It will either read 0 or 5 volts when you rotate the distributor. Find the spot where the meter wants to flick back and forth between 0 and 5 and tighten it. Should be within the 2* that the computer needs.
 
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