technical questions, help!!!

[svtcobra228]

Ok finally have some days off to work on the SVO. Current problem stuttering at low rpm, worse under boost. after 3500 rpm pulls hard up to redline. As noted in an earlier post ive put in a Walbro 255 that does not hummm when i turn the key but it does run so its working. Full tune up with motorcraft parts. Today im going to look at the TPS, my question here is if the tps is out of range will it set off a code on a diagnostic computer? When i had it on a computer before it read VAM high and low signal, and cannot locate knock sensor. All codes reset except the knock sensor. Im also going to do some fuel pressure testing. My idle is fine, smooth at 1100rpm. Im not sure what it should be at but i remember my turbo coupe idling at about the same. What is the stock engine speed? The sticker under the hood is long gone. Any imput to what i should look at today would be appreciated. thanks,
jason

[GAboySVO]

Knock Sensor

If your knock sensor is sending bogus info to the EEC-IV, it could be trying to adjust timing, fuel, etc. and causing your problem. If it is not disconnected, disconnect it and see if there is any difference.

I think I read somewhere that base idle with the IAC unplugged and the TPS adjusted to 0.90vdc is 700-800 rpm. When you plug the IAC back in, it should give you the correct idle speed.

The TPS will set off a code if it is out of range KOER test. I'm not sure if you get a code during KOER test. Look in the FAQ section for how t adjust the TPS. If you have a bad spot in the TPS range then you will only detect it using a analog volt meter.

A couple of post this week and last have led to the ECT being the problem with loss of power and stuttering eventhough no error codes were reported. You might check it out. It is cheap enough from AutoZone that you might replace it anyway.

As far as the fuel pump not humming, i'd guess a ground wire problem. Was the car doing the same thing before you changed the fuel pump? Did you take out and clean the injectors and fuel rail yet?

Just my 2 cents.

[svtcobra228]

update.....

Ok, did a lot of testing yesterday with my mechanic. The TPS is bad but thats not the problem exactly. We checked the timing, its correct at 10 degress base but the car advances 48 degrees when reved up to run. If we pull the spout the car will run like crap and backfire when it hits the 3000 rpm mark where ive had the problem in the past. The scanner didnt pick up any codes except no knock sensor detected and its a hard code.....keeps coming back. You would think that if the knock was bad it would retard the timing but instead the car wants more timing to run and hardly runs at all with the spout out. we changed the coil, uncloged the egr, unhooked the tps and tried a new baro sensor. The cam is in time as well. So now here we are, the mechanic is going to try a few more things today but i had to come back home so we will see. He's got an old turbo coupe at his house and is going to pull the computer but the car is an automatic so im not sure of the pin differences. Any more ideas of what we should try

[richsvo]

Are you saying that the timing is at 10* with the spout connected? It should be at 10* with it UNPLUGGED, if that's what you're saying....

Wasn't sure what you are indicating, so if I'm way off, then disregard...

Rich

[svtcobra228]

10 degrees was the base timing according to my mechanic. Im going by what he told me. Im thinking the spout was out.

[SVOeric]

you can't swap computers without doing several re-pins out of a TC


You need to make sure that timing is at 10, with the spout out.

if that is correct, the next thing to try is the TFI module, then the PIP sensor inside the distributor.

[svtcobra228]

i have a new tps that will be installed. he was going to try a new distributor today and see. He said he had never seen ford not run with the spout removed, anyone else seen this before? Mike, you mentioned injector drivers, if there is a problem there would that make the car stumble at 3000 rpm, the problem is constant and at around 3400 it clears up and runs strong all the way to redline.

[SVOeric]

if it won't run with the spout out, you need to check your ignition system (rotor button, plugs & Wires, ) and then follow this procedure to set the TPS --

http://www.svoca.com/forum/showthread.php?threadid=11

Your problems are sounding more and more like a improperly set TPS...

[svtcobra228]

the car does run with the spout out but barely. my mechanic said he had never seen a ford run that bad with the spout out. also with the spout out when you rev the motor and it hits my 3000 rpm problem it sputters violently and backfires. with the spout in it doesnt sputter at all when you rev it but if its in gear and driving when it hits 3000 its cuts out. i think he was changing the distributor next. i just left the car with him, ive done all i can do myself with limited mechanical expertise. I think im having the valve stem seals done while he has it too. I should have an update from him monday.

[svtcobra228]

update

Latest update on the stumbling problem. Still isnt fixed. Its now had a new coil, baro sensor, replaced plugs again. New distributor, pick up and module. New throttle pos. sensor. Fuel pressure is ok and yet the problem still exists!!!!!!!What else is left, four mechanics have been looking at this thing, two of them ford mechanics longer than i have been alive. Any more ideas?

[SVOeric]

was the fuel pressure tested @ load, or just while idling ?

if all the ignition system is good, and compression is good, it must be fuel, or air problem -- which leaves VAM, TPS, FPR, Fuel pump, injectors, or the wiring connected to these componets.

I'm going to ask one more question -- is the engine getting warmed up ?? in other words, how far up on the temp gauge does the needle get after running for 10 minutes ??

[svtcobra228]

while we were working on it it ran close to red and then the fan came on like normal. the fuel pump has been replaced, also the tps. The Vam was also looked at and appears to be working ok and it didnt run a code on the computer. Im not sure at what point the fuel pressure was checked, i wasnt there when the mechanic did this. He was going to check the injectors and FPR next. Its just strange how the stumble clears up after 3400 rpm every time. Light hesitation under 3000, at 3000 exactly it stumbles and bucks violently and then after 3400 it runs perfect.

[svtcobra228]

So this symptom isn't related to throttle position or boost pressure, but rather is repeatable according to RPM? Am I understanding correctly?

Exactly Mike!!

Ive already disconnected the EGR, it was stopped up so we took it off and cleaned it out. Works fine now but still not the problem. Out of my curiosity, what would the alternator be doing that might cause the problem, or other pulleys or sprockets that you mentioned? Also the distributor was replaced.

[svtcobra228]

another update

Well guys, thanks for all the help. I got the word from the mechanic today. Looks like it was dirty fuel injectors. He had to clean them three times but he thinks he has fixed it. He said he was going to drive it around today to see if that fixed it for sure. Next i guess valve stem seals should be done. thanks again guys.
jason