My 331 ran great - TPS didn't even work - fixed - now it runs rough!!

[Cobra912]

Ok this is a wierd one:

1) finished my 331 in my 86 about a month ago. all stuff in sig running an A9S cpu and converted to mass air following all instructions to a T. (repinned, fuel pump relay etc. etc.)

2) all new everything! plugs gapped to .38 (all), running MSD 6A, tfi msd coil, MSD pro-billet tfi dizzy and 30lb injectors. Timing set at 14 degrees. Pro-M 75mm mass air cal. for 30lb, with JLT intake (inside fender) comp cams nx264hr

3) fuel pressure was set a very high 55 psi to keep it from bucking when driving.

A) Car ran awesome for a car with no tune. I could travel at 30mph in second gear and mash the gas spinning the tires like no tomorrow. However when not under WOT the car would fall flat on it's face for 2-3 seconds when shifting from 3-4 or 4-5 and then take off like a bat out of hell! or when I shifted from 5th to 4th it would also fall flat.

B) The car also idled super high (1400-1500) but we accredited it to the lack of tune. I went through the surging idle checklist but no changes. no vacuum leaks.

ANYWAYS yesterday we were looking at a couple things when we realized that the car had cruise control from the factory (a long time ago) and the stock throttle cable was not adjusted properly causing the throttle blade to bind and not close all the way. Now the car idle great at 800!! YEAH I was so happy because it had been driving me nuts pulling up to a stoplight at 1500rpm.

Then I pulled all the plugs after reading that several people had problems with the car breaking up at speed due to improper gapping of plugs. I gapped them to 50 hoping it would help. The plugs (autolite 3924) were not soiled and had no indicators of anything wrong other than the tips being slightly white. re-installed.

We took the car for a drive. again ran great but still problem A. So we decided to check the TPS. Checked the prescribed method and found that the voltage was all over the place and could not get a consistent reading between .6 - .9 When we tried a "sweep" of the throttle the readings were all over the place. It was obviously apparent that the TPS did not work at all! I had an extra TPS so we switched it out. readings were all with in spec at .8 up to 5 volts.

Took the car for a drive - Viola!!! The car did not fall on it's face. Problem solved....................... or so I thought.

C) HOWEVER it now surges, almost feels like a miss when going through the gears at partial throttle. It doesn't sound rough but feels rough. Get into it hard and you can't feel it.

I bumped the fuel pressure down to 40 psi thinking I had been masking the TPS problem with fuel pressure. Still no difference.

What the heck is going on? Should my car have run as good as it did with a faulty TPS? I haven't been able to get the code which I know there will be as I have elimanated the egr, fuel canister, etc. etc. But any guesses??? Is there any problems with the way the mass air sensor is pointed or positioned as I thought I read somewhere that it did.

 

[jrichker]

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

Do not jumper anything to the single black connector. It is the power for the under the hood light. It is in another bundle of wires near the windshield wiper.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see EQUUS DIGITAL FORD CODE READER (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

 

[Cobra912]

UPDATE ***************

Have not dumped codes yet - will pick up ford code reader tomorrow night and see what happens.

I just took it for a drive with the "new" used TPS. Same thing, runs like crap, feels like it's missing,surging etc. which it was not doing with the old TPS.

I un plugged the TPS and problem went away car ran great but would hesitate big time in the upper gears. Rev'ered up to a 4500-5000 launch down the highway and nothing - no problems, hauled azz. partial throttle - problems.

I did not realize the car would run without a TPS. I will dump the codes tomorrow and see what I get.

Please stay tuned!

 

[Darkwriter77]

Bear in mind you're going to probably have codes stored from driving it with the TPS connected ("TPS - low or no voltage"). Reconnect the TPS, reset the ECM (disconnect battery cable for awhile or pull the ECM fuse to clear it), then take 'er for a spin, and THEN check your codes.

 

[Cobra912]

You were right Darkwriter.

I got the reader. Checked the codes:

63, 31, 81, 82, 85, 84, 95

I understand the 31 thru 95 which are all a result of having elimanted the whole egr, air pump, fuel canister, etc.

The 63 was there with key on, engine off. I reset the battery with my cutoff switch. Key on engine off - no codes. The good TPS now on the car.

Ran key on, engine on test. Same codes but no 63.

Car sounded great but I was unable to take the car for a drive because 3 kids and only two seats! haha can't put a baby seat on the poly race buckets.

So I hope tomorrow after work I can take it for a drive.

 

[Cobra912]

Oh by the way I used a Sunpro made by Actron for the tests.

Two questions:

1) If there was a bad TPS on the car, it gave off an error code (and same as diconnecting it) and the car "adapted to it" would it be possible that putting a new TPS and not reseting the memory (by disconnecting the battery) would still cause a problem or code without the cpu autmatically correcting it?

And if by putting a new one on and reseting the memory (elimanting the code) is it possible that this could solve the problem? Remeber it was only under partial throttle. The car idles great and pulls hard under WOT.

2) Fuel pressure. I now have the car set to 40psi at idle. I thought I read that no matter what pressure you have it set at the cpu will automatically decide for itself how much it needs. Given my combo does it make sense to have this psi? I sure wish I had a wideband.

I also read in an ongoing tech question regarding O2 sensors being unplugged for open loop. Does this sound like something that would work?

 

[Cobra912]

Wow...........this one has me stumped.

Thinking of reducing gap from .50 back to .38 where I had the plugs. Also thinking of upping the fuel pressure.

Unplugged MAF (75mm Pro-M bullet) which caused the car to run even worse so it must be running properly.

I've done some research on here and I have read everything from unplugged sensors to vss to dizzys.

I'm running a pro-billet MSD TFI with a 6A box, blaster coil and autolite 3923 plugs.

 

[Cobra912]

Anyone????

 

[Cobra912]

Ok I spent HOURS diagnosing the problem.

1) I pulled the msd wiring adaptor harness off and connected the coil without the msd 6a box - no luck

2) pulled all the wires and plugs checking for cracks (even though they are all new) - no luck

3) TPS checked, all good - no luck

4) bumped up fuel pressure - no luck

5) completely removed my JLT and aligned the Pro-M bullet 75mm mass air so that it was at more of a 45 degree angle versus the 90 degree angle I had it at - again no luck

6) checked codes again, all same, just egr, emissions etc. - no luck

Decided to dig deeper, my Dad came over and he immediately checked the distributor. WELL GUESS what!

The rotor was installed improperly with one bottom tab in the wrong hole. It was making contact with the cap and it was full of plastic shavings. Pulled it all cleaned it up, installed properly and checked timing.

Took it for a drive down the highway - PROBLEM SOLVED!! it ran hard and even in 4th gear it'll put you in the back of your seat. I was so happy.

Now.................off to the strip for the first time ever on Sunday!:Track: