Head gasket? MAF? Need some Mustang tech help :)

Barrier · Dec 13, 2006

So I've been having this problem for a while with cold starts... My vehicle is in a garage usually, however about 3 weeks ago I left it in a parking lot. (cold temperatures... Michigan) The next morning when I started it, the car idled immediately at ~500 RPM, no throttle response, and seeming like it was camming like a muscle car. No MIL light came on throughout. This kept on for around 10 seconds then the car was fine. Recently it has been happening even when the car is in the garage and just this morning it wouldn't stop until I turned the car off. It then began surging and intermittently doing the same camming sound with no throttle response, whether accelerating or coasting. Still no MIL light. This continued until it reached OT.

I hooked it up to my computer tonight with the ECT reading ~140 and immediately it began doing the same thing at idle ~540 RPM. I noted that the short term fuel trim on bank 1 was reading -20.3% (lean) and bank 2 was reading 30.7% (rich). TPS was a bit off reading 13.8% at idle and 93% at WOT. The IAT, ECT, MAF, and MAP all read fine... I'm guessing the head gasket on bank 1 had a pinhole leak that would seal up at OT but progressively got worse. A colleague suggested before the test that the oil on my K&N filter (I cleaned and re-oiled it 2 months-ish ago) could have leaked through and residue could have hit the MAF sensor. Any thoughts?

jstreet0204 · Dec 13, 2006

MAF would throw off both banks. I would lean toward a lazy o2 sensor before a head gasket.

Barrier · Dec 13, 2006

Checked both upstreams with the scanner (downstreams have eliminators)

And would that cause all the rough starts and surging anyways? I wouldn't know

jstreet0204 · Dec 13, 2006

Barrier said:
Checked both upstreams with the scanner (downstreams have eliminators)

And would that cause all the rough starts and surging anyways? I wouldn't know

They may be switching but that doesn't mean one isn't out of range. One could just be lazy and not switching fast enough throwing off the fuel trims on one side. That would cause a rough idle, but only after it goes into closed loop. If it starts fine, that after a few seconds, or minutes depending on how cold it is, starts to idle rough, it is probably one of the o2 sensors. If the rough idle starts immediatly it is probably something else. Have you checked the fuel pressure at idle.

Mike97gt · Dec 13, 2006

to get the fuel trim readings correct you need both long and short term fuel trim.

Long term is what is already learned by the adaptive strategy, and short term is correcting the PCM is making to the learned value at that moment..

So if you see -20 long term and -10 short term your total fuel trim is -30.. this means that the PCM leaned the mixture out 30 percent. positive numbers is fuel added on top of the base map negitive numbers is fuel subtracted.

If you can get the total trim readings for both banks that would help out alot.

I have a feeling that you have a large vacumm leak or somthing that is screwing with OL operation. The PCM should make adjustments to OL based on what is learned in closed loop operation but somtimes if the problem is too big for adaptive to overcome then this can happen.

Start out with the basics like checking the intake tubing and all vacumm connectors. Plus if you can check fuel presure do that and see what you come up with. On your car there is a PID you can look at with a scanner ( atleast you can with the ford ones) that will tell you the fuel presure the PCM sees at the rail.

Barrier · Dec 14, 2006

Thanks to both of you for that much needed information

jstreet: The rough idle starts immediately then usually goes back to normal after around 10 seconds, but yesterday it happened both at start up and intermittently until it got to ~200* on the ECT

svttech: I'll see what I can come up with on the long term, but they were both reading 0.0 the whole time on the device... anything I can do to find out the numbers or is it just not reading it? I'll check out all vacuum lines today when I get the time and possibly clean the MAF just to rule it out.

Also... one person suggested I wan't getting enough voltage to the ECU. I do have a corroded negative terminal and will be replacing both cable ends and cleaning everything today. Any possible way that might be it?

jstreet0204 · Dec 14, 2006

Barrier said:
Thanks to both of you for that much needed information

jstreet: The rough idle starts immediately then usually goes back to normal after around 10 seconds, but yesterday it happened both at start up and intermittently until it got to ~200* on the ECT

svttech: I'll see what I can come up with on the long term, but they were both reading 0.0 the whole time on the device... anything I can do to find out the numbers or is it just not reading it? I'll check out all vacuum lines today when I get the time and possibly clean the MAF just to rule it out.

Also... one person suggested I wan't getting enough voltage to the ECU. I do have a corroded negative terminal and will be replacing both cable ends and cleaning everything today. Any possible way that might be it?

It sounds like the problem may be with open loop idle then. Try checking the tps voltage if you haven't already. Get the battery cable fixed first since that is a good possibilty also.

Barrier · Dec 14, 2006

jstreet0204 said:
It sounds like the problem may be with open loop idle then. Try checking the tps voltage if you haven't already. Get the battery cable fixed first since that is a good possibilty also.

Will do whenever I can Thanks again, I'll make sure to reply with results.

Barrier · Dec 15, 2006

So I ran it again, and it does look like I have a lazy O2 sensor on bank 1. Apparently somehow I overlooked this last time, but it's only reading up to 600 on bank 1 when it should be ~900? At any rate the fuel trim is constant 15% rich for that O2. Might be my problem?

jstreet0204 · Dec 15, 2006

Barrier said:
So I ran it again, and it does look like I have a lazy O2 sensor on bank 1. Apparently somehow I overlooked this last time, but it's only reading up to 600 on bank 1 when it should be ~900? At any rate the fuel trim is constant 15% rich for that O2. Might be my problem?

The easiest way to tell if it is the o2 if you don't have all the fancy equiptment like SVTTech has, is to just swap the two front o2's. If the problem follows the o2, to bank 2, then you know that sensor is the problem.

Rickey_Bobby · Dec 16, 2006

barrier, what scanner are you using?

Barrier · Dec 21, 2006

I'm using AutoEnginuity's base scanner.

Also: My O2 wires are a bit singed but I saw no melt down to the inner metal... they were melted by the pipes before I zip tied them down. However being this is right when I start the engine up and thus still in open loop, I figure it's an unrelated issue

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