Texas_Ace

Ok, got the new TPS, installed it and the truck is now drivable!

But the strange part is i was test driving it and after a little bit i noticed that it started stuttering again slightly at maybe 10% throttle?

Anything other then that and it runs great but at a certaint point it acts all funny. Anyone know where the test for the TPS is on the FSM?

Texas_Ace

Ok, this is really starting to get annoying.

So went back out and started looking at it again, and now it is acting just like before the new sensor?!?

So guess it was not the sensor afterall. Ohmed the old one and it seems to be fine, i hooked up the OBD reading and the TPS seems to be within spec, it says right at what it should and no other readings seem out of place.

What what in the world could be causing this???

Once i get past about 30% throttle it revs/drives fine, under that is stutters and bucks like crazy! and it dies if i try to drive it. I have reset the ECU, it just seemed to make the problem worse.

Anymore ideas?

Texas_Ace

Well just got back from some more work on it and found somthign interesting.

It actually appears to have nothing ot do with the gas pedel at all.

It seem to be ~1800rpm is the magic number.

If i get it to rev past that, everything is golden. doesn't matter what i do as long as it is above about 2k rpm.

Below that if i do anything it bucks like a bronco. Idles fine though.

What in the world could cause that?

Fule filter, plugs, plug wires, all of those would either work or not, they would not act like this (at least i have never seen it).

So what would keep it from running right below 2k?

atistang

I'd say its a ground problem

Texas_Ace

Ground is possible but how would that only effect it in that narrow RPM band?

Maf was cleaned and checked on the OBD, everything appears fine.

Coolent temp also is fine, was saying 190degrees which is exactly what my gauge said.

Texas_Ace

What plugs should i run with the supercharger? I am going ot replace those just to make sure while i highly doubt it will help anything.

atistang

oh i didn't know it was supercharged

atistang

if it isn't to much trouble you might try bypassing your msd box

Texas_Ace

LOL, that thread in my sig is well over 2 years old, the MSD has long since been removed.

ok, just tried some new plugs, while it seems to run better it still has the problem just as bad as ever.

I am now totally lost, once it gets above 2000 rpm it runs perfect, lots of power.

Below 1500 it runs/idles fine.

Between 1500 and 2000 it runs like junk and will stall somtimes.

I am totally lost.

Texas_Ace

Ok, i just decided to hook up my inline spark tester.

And between 1500 and 2000 where the problem is, the casuse of the stuttering is no spark. Above and below spark is normal but between 1500 and 2000 it will lose spark for no reason here and there.

Now what could cause it to just lose spark?

gilby4runner

random chance but would your fuel system (urd) have anything to do with it?

Texas_Ace

Thought of that, so i hooked it up to the computer and check all the signals it gets and everything was normal, it also doesn't tie into the ignition system except for the timing advance so don't know how it would cause it to lose spark.

I do know it was not adjusting any signals while the problem was happening. so it seems ot be in the clear.

I just got back from a good test drive and funny thing is the longer i drove the better it seemed to get, sometimes i could not get it to do it.

I also narrowed down the problem RPM to between 1600 and 1800. What happens in there?

I think i am going to take a chance and go pick up the car as it is but would really like to fix it.

So anymore ideas? Why does it randomly lose spark at 1600 - 1800rpm?

atistang

if your urd controls timing advance then that could be the problem since there seems to be no cel related to the spark issue

maybe a crank sensor


i'm still leaning towards a ground problem, with all the electrical stuff you have added maybe something has came lose or gotten corroded or maybe is drawing enough juice to cause problems?

typically with more simple codes if the part doesn't fix the problem then its a ground issue

Texas_Ace

I thought of the timing advance as well but the OBF said that the advance was spot on.

Crank sensor or coil is what i am leaning towards at this point.

A ground is possible, the problem is finding it and fixing it. Where do you even start to look?

All the stuff i added is wired seprate from the battery with there own fuse block, so highly doubt they are casuing any problems.

If the stuttering happend allalong the rev range or really anything but this REAL narrow RPM band it would be easier to understand but only within 200 rpm's?

atistang

for the ground you just need to start with the batter cable, then start tracing every harness and anywhere you see a wire attach to the engine or body or frame then check it to make sure its not lose or corroded


also check for any broken wires that may be a ground

Texas_Ace

Yeah, already checked all the obious grounds but it is never one of those is it?

Guess i will play find the ground later. fun.

atistang

not normally, when i put an engine in my mustang i kept getting tps and maf codes, after a few weeks of playing around with different things i found one little ground in the injector harness that was hiding in the wire loom that was suppose to connect to the back of the intake

hooked it up and problem solved

Texas_Ace

Thats what bugs me, it doesn't toss a code.

and i have never heard of somthing like this.

Lumpy

This is quite odd...and it only happens in such a small range. Makes me say Hmmmmm, i donno, quite interesting. Could it be the wiring from the coil to the distributor. Could it be the distributor?

To be honest I have not worked on a 3.4 so I'm not real sure of the setup. Just trying to give some ideas.

Texas_Ace

The 3.4 doesn't use a distributor so doubt that is the problem lol.

But the coils ARE suspect.

So today went out and started it up to go pick up the trailer.

And what do you know, runs perfect again! I will take it but i sure hope it stays away this time. If not i might go mad trying to fix this.