Long time member, but I have not been on here in years because everything has been running perfectly.
Well that has changed and I need some help figuring out this problem.
AMC/Jeep 401 V8. 16197427 ecm running $0D. Started out as TBI but later changed to MPFI by swapping out he resistors in the ecu and doing the needed programming changes in the BIN.
So everything has been great for years, running great, very reliable, super fun.
So randomly a month or two ago, I noticed what sounded like it was dropping a cylinder or two at cold start. Sometimes it lasted a few seconds, sometimes you had to start driving for a few seocnds then it suddenly cleared up and ran fine.
One day it started doing it when I was about halfway into town and did it the whole way back home. I did not have time to check anything at the time.
The next weekend I look everything over, all the spark plug wires looked good. Distributor cap and rotor look good. I cranked it up and it ran fine.
It did this off and on a few times, then on the 4th of july, I went to drive it to lunch, and it was missfiring hard. You could hear it cut in and out. Like whatever the issue was, was coming and going intermittently.
I messed around with it and unplugged each injector 1 at a time seeing if I could narrow it down to one cylinder. I could not.
I checked the spark on a couple cylinders and it seemed good.
The issue/misfiring seems ignition related, as the AFR on the wideband still looks good. Not running rich or lean.
I am running a HEI distributor I modded several years ago and running the 7 pin module.
I had a spare coil, so I figured I would swap it out, just in case it was breaking up. No change.
When I say misfiring, it is not backfiring or popping, but just sounds like it is not running on all cylinders and has no power.
I tried running it after swapping the coil and it is still doing its misfiring thing, but then I just randomly look down and saw the tach jump.
So I thought, heck, I bet I have a bad pickup coil. I swear I want to think I saw the tach jump, when it cleared up for a second.
So this past weekend, I pull the distributor, swap out the pickup with a spare I have and reassemble. I marked the location of the distributor and rotor and get it back in as close as I could to where it came out, so I could get it going enough to reset the base timing.
Well, still no dice. It actually runs worse now. It will barely stay running, and now wants to pop out the exhaust a little.
I'm sure the timing might be off a degree or two, but it should not be enough to cause this issue.
I go ahead and swap out the 7 pin module with another spare I had just for poops and laughs with no change.
I finally break down, dig through my storage and find my autoprom. I fire up the laptop and hook it up.
It is showing error 33, MAP high.
I think, dang, was that my whole problem all along, a bad map sensor?
I swap it out for a spare I have with no change. I disconnect the battery to reset the ecm with no luck.
So I turn the key on, connect to the ecu (engine not running), hook up a hand operated vac pump and apply vac to the map sensor. I get no reading, it just shows map 100.
I try both sensors with no readings from either one. The spare I know was good when I put it in storage.
I check the connector and I have the 5v refrence, and have ground.
I unhook the ecu and check the signal wire, thinking it is broke. Nope, I have continuity and it ohms out with no resistance.
However, I can get no map reading on the datastream. I have bench tested several ecms in the past and using a vac pump on the map sensor, always showed it on the datastream. But it will not show anything now.
When I start the engine, the map will read, but it stays at map 80-90. So naturally, the engine runs like pure crap, cause it thinks the map is that high while at idle, and the fuel/spark is being adjusted to try and account for that.
Last ditch effort, I break out my spare ecu I have (yea, I like having spare parts). Same thing with the other ecu.
So I am pretty much at a loss and at my wits end. Why, if I am getting power and ground, and the signal wire seems fine, am I not getting a map sensor reading in the ecu/datastream. But with the engine running, I get extremely high map reading, but only when the engine is running.
I even tried hooking up the vac pump, then starting the engine, and it still reads high map (and runs like crap).
Just looking for any help or suggestions.
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