02 MGM Help needed

[Prgrmerror]

I could really use some help trying to figure out what’s going on. A month ago I had what I thought was torque chatter. It happened so fast by the time I got off the gas it was gone. I read what I could and waited for it to happen again. I also checked fuel pressure and it was 30psi. Fast forward to today. It stalled in a slow left turn in the neighborhood. I didn’t realize it but the yellow check engine light was lit. I pulled over and it started right up. I turned the A/C on and got about a block when it acted up again. It wouldn’t take the gas pedal. Almost felt like I was driving into a severe headwind. I turned off the A/C, came off the gas and it cleared up. 10 minutes later it happened again. Wouldn’t respond well to giving it gas. It did act normal when I came off the gas. I drove it around for another 15 minutes and it acted fine. I initially thought fuel pump but the more I read the more I couldn’t exclude the crank position sensor. I have no idea how to proceed. Anyone have a similar issue? My wife uses the car often and I do t want her to have trouble on the road.
Thanks

[jaywish]

Check the codes for a start.

[IPreferDIY]

For a situation like this, it would be helpful to have something to plug into the car's computer to see if you can learn anything that way. A simple code reader would not be all that great, but there might be a "pending code" to indicate what's up. A scanner is better, since it tells you all kinds of operating parameters in addition to accessing codes. IDK what a typical scanner comes with, but mine can also access "onboard monitor" info, which has been particularly good for localizing misfires to particular cylinders.

I recall reading that the engine would not function at all with a faulty crank position sensor, but I'm no expert. Have you checked basic things like fluid levels (tranny and coolant come to mind in particular) and cleanliness of air filter?

[Prgrmerror]

No idea how to check codes. No lights on the dash are lit. Check engine is not on. The car had every conceivable maintenance item replaced 3000 miles ago All fluids, filters, plugs, coils, belt, AC clutch. it’s been running like a new car. Gas mileage is around 17 miles per gallon in town the car has been very normal. I was hoping that whatever it was was common to the car and that many here might’ve seen it before. I’m stumped I wish whatever it was just broke so I could find it and fix it

[EaOutlaw1969]

Could be anything wrong, start with checking the codes, if you do not have a reader maybe autozone or another shop will read them for you for free?

[Prgrmerror]

Thanks. Autozone is nearby. I’ll head there in the morning. Thanks for the suggestion.

[mercurygm88]

It's possible you could have pending codes and they just haven't tripped the check engine light yet.

[Prgrmerror]

Back from Autozone. They let me scan it and unfortunately there were no codes. It drove fine today. I’m going to do a visual inspection and I’m thinking about replacing the crank position sensor and dreading replacing the fuel pump but may take it on. I hate throwing parts at it but I can’t really sit around and wait for my wife to get stranded with it. If anyone has any thoughts please post. Thanks

[87GrandMarq]

My two guesses would be either the fuel pump or maf but I’m leaning more towards maf. Do you have any way of datalogging?


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[sly]

This really sounds like a wire wiggle test waiting to happen. Something is probably corroded or some wire loose somewhere. My wife's 2000 CV had the OBD-II wires break for some odd reason and they had to run new wires. Could be the same issue working itself into action between the PCM and the engine. Or the TPS/MAF/ECT/CAM/Crank (some sensor) is in need of a clean, replacement, pigtail connector.

[EaOutlaw1969]

You have a older car which any part at any time could leave you or your Wife stranded, even with a new car there is always the chance of getting stranded.
With this in mind it may be a better idea to spend money on a AAA gold membership and make sure the cell phones stay charged.

As far as diagnosing the problem You are on the right track with checking the basics.

I would start with pulling each and every fuse and checking for corrosion replacing or resurfacing suspect fuses. I would also check the battery connections and all the grounds.

I would also do a wiggle test on the harnesses throughout the car as the car is running.

The one thing that does stand out is the fuel pressure you found I would think 30 PSI is low for a fuel injected car But since I do not have a manual for a 2002 I do not know for sure. So please confirm with a manual for the rated fuel pressure.

In the years of working on cars it seems when ever I came across a weird problem it was normally caused by the last person that worked on the car, anything from loose connections from broken harness tabs to missing bolts and pinched or otherwise shorted wires even vacuum leaks could be causing your problem.

With this in mind double or triple check all the previous work done to the car even if you know it was done right check it all again anyways.

if this was my car and I had done all of this work and suspected fuel pressure or loss of injector pulse I would rig up a fuel pressure gauge and tape it down to the windshield you could also do the same with a noid light to check for injector pulse.

But first like I said recheck the manual for the correct fuel pressure as 30 psi sounds too low. others here may have better ideas.

I may add a worn TPS ( throttle Position switch ) could cause a loss of power and perhaps a shutter at low throttle and not cause a code hard to find with a DVOM but easily found with a lab scope. If you find nothing wrong with the fuel pressure or wiggle test and had to toss a part at it a TPS is a cheap and normally easy one to install and well worth doing if the part is original. but stick with a Motorcraft part.

[Prgrmerror]

The crank pos sensor connector looks a little wet with oil. Must be from previous work. Not really sure. The sensor itself had a pretty gunked up tip. I am just replacing it and cleaning the plug. If it happens again I’ll do the fuel pump assy. Hate not getting to the root cause with clarity but I need this fixed.

[EaOutlaw1969]

I forgot to mention one or more of the spark plug wells may be full of water or oil and could cause intermittent issues but would normally be caught by a code. may be worth pulling them out one by one and inspect each boot for signs of moisture or oil.

[Prgrmerror]

Sensor replaced and both banks dry. There was oil in 2 when I did the plugs in the fall but I took care of that then. The car started, ran, and drove fine. I did 4 miles in the neighborhood with the A/C on max. Running perfect. Hope it doesn’t do that again but if it does and still no code I’ll do the fuel pump. Thanks for the sounding board. I’m not a wrench but with YouTube and this forum I’ve managed to do fairly well with repairs and maintenance.

[Prgrmerror]

I re read the thread and will do the wiggle test while running. The 30psi is on the low side of okay. I think it may be a good time to order some sensors; the car seems to be mostly original and has 150k. This is the dog car for us. A breakdown means with 3 large dogs. That can’t happen. Lol