Ok well i was having a little problem while Autoxing this weekend and then worse on the way home......

The car was "cutting out" at interstate speeds like 70-80 mph in 5th gear, just like for a split second and the tach was bouncing around like crazy....

I know this

I just changed out the intank fuel filter - not that then
The injectors were just tested and are good

It felt electrical, especially because of the tach....
It only did it on course in 2nd gear above 5k
I kept checking the plug wires and they were on but had "play". Tell me what you think i need to do.

I bought a new fuel filter just to be safe..... Let me know..

 

Using test lights or voltage at idle readings will get your idle setting done, but may not show a worn out TPS resistor.
I pull the TPS connector off and clip on an analog (needle type) VOM set to the 1K scale.
The reason is because as the TPS wears, it can give non-linear or inconsistent signals to the ECU.
You can see this as you work the TPS plunger in & out, the needle should swing smoothly from 0 to ~5K ohms.
A worn out TPS may give 1K ohms at idle, but have a drop out or short further up the scale.
I had one go open at the top which made the S5 ECU go nuts, giving random fuel cuts.

 

Ok replaced the TPS and it didn't solve the problem. I have been searching around and can't really locate the problem,

please shoot out some ideas or similar problems and solutions...

i am going to relpace the fuel filter and the spark plugs in the am.
What does it feel like when the coils are going out?
What about the alternator would over or under voltage cause this?
How about spark plug wires?
What does a fuel pump feel like when it's crapping out?

thanks

 

Oops - I should have seen that earlier - It rules out the TPS.
Hmm - Isn't the tach triggered from the trailing coil?
I'm not sure, so check me on that.

How about loose primary grounds?

 

Are you taalking about the grounds on the primary injectors?

 

Are you talking about the grounds on the primary injectors? How can you tell the difference between electrical and fuel related hesitations...... . thanks for all the sudjestions..btw,.

 

You know what......I JUST RAN injector cleaner through this thing on saturday night, That's about when the problems started.... Could the cleaner have bunged up the fuel filter? Man this really sucks.

 

The tach jumps imply an electrical issue, but it could be both..

 

The spark ground is through that cheesy clip-on firewall ground, unless you have added other ground wires.

 

Is this exclusive to 5th gear? (dont see how)

 

honestly sounds like something got wet that wasn't supposed to...check wiring in the engine bay for something grounded out ot exposed insulation.

 

No it's not in only 5th gear, it's randomly throughout the rpm range. Is this the sign of a failing cpu maybe? I am really at a loss here. I have gone over the haynes and it is worthless.

Here's the exact situation. The car accelerated hard, then "misses" for a mili-second, then resumes normal for a second the "misses" for another mili. It almost makes the same sound a rev limiter does. My gas miliage is better then ever (20mpg) All the plugs and wires look good, the in tank filter is new (this is when the problem started.) And I am replacing the "under hood" fuel filter in the morning. Please help i don't know if i can continue to drive it like this.....

trevor

 

Okay, lets get more info here:

Above 3800? Below 3800? Only above 5000? Happens anytime? Only during acceleration?

The Tach jumps correspondingly? Thats whats worrying me. I would like to think of it as a misfiring injector, but with the tach jump... Hmmm..

What EXACLY have you changed since this started happening?

 

below 3800 but never below 2100- above 3800 anytime any condition, hard driving or granny style, primarily in 2-5th at medium to full throttle though. it only does it if i am giving it gas, but giving it gas may only be for holding a constant speed, not accel per say. The tach will go from say 2k where i was driving at to 0 then right back to 2k.

 

Okay, right now I am leaning towards a loose connector or failing trailing coil, but here is an outfield guess:

How are your plug wires routed? Sometimes if you run plug wires next to each other in long stretches, the can "crosstalk". This means the spark will jump the wires.

 

Hey man sorry to hear about your car acting like that, I hate it when my car gets fuked up. But a while back I had a similiar problem, and it was electrical. It happend right after they stole my radio. The car would run fine, but when I punched it, it was like if I had a two-step on. Then the tach guage would stop working. Well I changed everything, from coils to plugs. and even the ecu. Until I gave up and sent it with my mech. Apparently the was a short in the harness and it was all fuked up. He re placed some wires and it was all good. I really didnt ask him wat wires he replaced, so I cant help you out there, but try checking out the main harness.

 

Well i will look at the plug wires, I have them routed close together, and tye wraped , but they have "dress up" plastic sheathing on them. I have a trailing coil out of a parts car i am going to try too....... Also do your spark plug wires "click" on the plugs? Mine don't....

 

Of course mine do.

 

Ok well, new plug wires tommorrow too i guess. If that's all it is i am going to kick my own ***. I was going to hold out and get some "performance" wires but it takes about a week to get them...I'll buy some cheapies and see if it fixes the problem......I am also making a HUGE grounding kit with supplies from work, my car will be so grounded it'll be like a 10 foot copper rod in pavement....

 

Still up for sudjestions if there are any additional.

 

OK well today i had a few minutes and started looking hte car over, I figured my plug wires were still good because they are only like 6k old. So i moved on to the plugs themselves, they were dry and had a "sand" colored buildup on them, i took a wire brush and electronic cleaner and gave them a good cleaning, the electrodes were still in good shape, I put them back in and procededto jack the car up to change out the fuel filter. Lo and behold what do i find? A ground wire leading to the fuel filter......where does this go? I don't know. Anyways it's a little loose, free swirling i might say. So instead of changing the filter i just tighten the connections on the ground and take her for a test drive,....... Well the hesitation seems to be gone for now, i'm not saying this fixed it neccesarily but it seems to have stopped it for now, I'll update some more if this proved to be a coincidence.

 

Update- The problem HAS gotten better but is not gone.... It only does it in 2nd gear now obove 5.5k rpm's

I bought new plug wires and installed them, and i also ran a thick ground wire to the fuel rail and then to the negative terminal on the battery. I am about to change out the fuel filter and the coil this weekend. If you have any other idea let me know..

trevor

 

Is the tach still acting up?

 

Not really..it'll drop according to engine speed now like when the car "misses" it'll drop like 100-200 rpm's, it seems to coincide with the miss now. Not bouncing around like crazy.....

 

Out of curiosity, have you checked the alternator voltage? Low voltage can cause misses and also cause your tachometer go wild...

David