My car shuts off while sitting at a light and sometimes while driving.

[mattd1979]

The car shuts off as if you turned it off with the key. It will start right back up and run good for a little bit and shut off again. towards the end the more frequently you try to start it the harder it is to keep it running. I Had replaced the TPS sensor and Maf along with the fuel pump and controller all around 10,000 miles ago. This problem popped up about a week ago. It all started with it simply shutting off while in park. I started it back up and it did find the rest of the night. The next day it became more of a problem. My Nephew drove it to the store and it shut off on him 3 times. Towards the end he was almost to the house when it began to stall he revved it up and it wouldn't go over 6500 rpm. I have a NICO ECU installed. I mentioned this in a previous post. Last night I had it running, so I revved it to see if it hung at 6500 as it did with him but it went all the way to 7300 like it was supposed to. As soon as I lifted my foot, it shut off. I started it back up and I had to keep pulsing the throttle to keep it at 3000 rpm and finally it leveled off and I could lift my foot and it would idle. I goosed it a couple of times as before and it continued to run with no problems. I can't seem to figure this out.

[maxnix]

Intake maintenance hsitory? Fuel filter replacement interval? Condition of tank and fuel lines when you replaced FP? Did you inspect FPCU? BG44K?

[mattd1979]

All underplenum hoses and rubber intake orings replaced, knock sensors replaced, knock sensor harness replaced, fuel injector harness replaced. All of the above was done almost 20,000 miles ago. Replaced 2 fuel injectors 2 weeks ago, fpcu replaced with fuel pump, all fuel lines are good. Replaced fuel hoses. Replaced fuel filter when I changed oil 2 weeks ago. I replace the fuel filter every 9,000 miles.

[goody90q45]

CEL on? Any ECU codes? Were FPCU and fuel pump installed new or used?

[mattd1979]

There were no CEL lights and no codes. The fuel pump and fpcu were pulled from a 1995 Q that we bought for parts. It was totaled in a car accident involving 2 police cars. The car had 62,000 miles on it when we got it. It ran good once we got it started though it was stuck in 4th gear from the accident. Everything else that I replaced was new.

[96Qowner]

I'd pull the MAF and CAS connectors and make sure they're clean and that the pins fit tightly and are conductive. The pins on the MAF connector in particular are only crimped onto the wires and have been known to come loose.

[mattd1979]

Alright, I'll check the connectors on the CAS and try to clean them up some more. I replaced the MAF with a good used one about 5,000 miles ago. There is some type of conductive grease that I saw somewhere that is suppose to increase conductivity but I can't remember what the stuff was. I saw it online one time. Does anybody have any ideas of anything out there that I could get that would do this? I am hoping that I can get this taken care of before this weekend because I am suppose to be driving up to Jacksonville (about 3 hours one way) to pick-up family members for my Nephew's graduation party. I know that there is an electrical problem somewhere because the engine is mechanically sound. I am thinking of swapping ECUs to see if that helps anything. I have just about done everything else that I can think of.

I am trying to figure for one, what could cause the engine to shut off. Could it be the ECU telling the injectors to stop? Could my coil pack modules be going bad? Could the CAS be the issue? Are any of the above known to go bad? I don't know. I'm at a loss for now. I wonder what I could disable so just the basics to run the engine are in the picture. Then, if it acts up again, I believe I could more easily pinpoint the problem. I wouldn't leave it like this. Just long enough to see if anything continues to happen. If nothing happens then I would re-enable each additional component one-by-one until the problem surfaces. What do you all think?

P.S. The spark plugs were also changed back when I did the underplenum job about 20,000 miles ago and I also updated the chain guides.
Modified by mattd1979 at 1:21 PM 8/26/2008

[96Qowner]

I mentioned the MAF because sudden shutoffs are a symptom. It's possible the replacement is bad, but it's more likely to be trouble in the connector. Intermittent wires would explain a lot. You might disconnect the MAF and see if it runs any differently. The CAS often exhibits some of the same symptoms, although the car won't run well at all when disconnected.

[mattd1979]

I disconnected the CAS last night while it was running and it shut off. It wouldn't run unless it was plugged in.

[maxnix]

Stabilitant 22, I think.

It's in TexasOil's posts.

[mattd1979]

Yeah, that sounds like the stuff. Thanks. I went ahead and started the car and listened in the trunk at the fuel pump to see if it shut off prior to the engine shutting off and found that when the engine did shut off, the fuel pump stayed on for another 3 seconds. I then unplugged the MAF and so far the car is running. When I did unplug it , the car shut off, so I had to restart it. When I went to plug the MAF back in, the car shut off again. Is this normal for the car to do this when unplugging and reconnecting the MAF? If I keep the rpms up to 2,000( that is as high as it will turn with the MAF unplugged) I can keep the engine from shutting off, though it tries to stall first and then regains rpm. The same goes for unplugging it.

[mattd1979]

Well, apparently it has been narrowed down to my maf. I removed the cover to the maf and disconnected the MAF. I found that there was a copper plate that covered the circuit board and it is attached with 2 solder joints at one end. Only one joint was still soldered when I removed the cover. While the engine was running and I connected it back up to the MAF I noticed that it would try to stall when I'd lift up on the plate and when I pushed down on the plate, it would start running normal. I don't know if the plate was doing this or it was just because I was pushing down on the board. I went ahead and removed the plate to gain access to the board and to see if there were any joints that were loose. I didn't find any.

[maxnix]

Perhaps unrelated, when I recently did the VC job on my VH41DE, it ran like a top for about a month or 6 weeks. One day, wife came home, Slip and TCS (and thus SES) lights are on and it died 3 times on here in the neighborhood.

Switched cars and when I drove it later. All lights on and drove like a champ. Later that night, it stalled and lost power. Next morning, I checked all connections visually, took it to get scanned, and MAF came up. Physically checked MAF connector, and it had not latched fully. It appeared seated, but it still allowed some movement. Latched securely now, all is back to normal with no lights.

[96Qowner]

Yup. it's the MAF!

Here are a few threads on resoldering the MAF:

Repairing MAF

Fixed MAF in spare time

96Q the nightmare continues

Still Jerking and Bucking 1996 Q45