Part-throttle bucking and hesitation

bonestock87 · Oct 3, 2011

As some of you may know, I recently swapped a 2.3 turbo in my 93. It runs great 90% of the time. I'm having an issue where the car will sometimes buck and not accelerate at part throttle. What is odd is how intermittenly it does this. It never does it/doesn't do it during the same drive time. For example: I can start up and drive to work and everything is great. I go out for lunch and it doesn't want to accelerate and bucks wildly unless I give it full throttle. I can shut the car off and a few mintues later it doesn't do that anymore. Furthermore, it can go days and not do it at all. So far I have:

Replaced spark plugs, wires, cap, rotor, fuel filter, cleand the IAC valve, ran fuel injector cleaner through it, and cleaned the throttle body. What I haven't done is to test/check the TPS. I'm using the stock throttle body from my N/A 2.3 on this turbo motor.

Advice?

bonestock87 · Oct 3, 2011

I retested my fuel pressure, it was dead on at 30 psi with vacuum line on the fpr, 39 with it off. I swapped the old Motorcraft wires back on I place of the "quality replacements" and also rechecked the plugs condition and gap. It seemed to run and idle much smoother and drove good. The fuel pressure rose as it should with boost. I believe I'll be ordring some new Motorcraft wires.

vristang · Oct 6, 2011

Did you get any error codes?
EGR still in use?

79'293stang · Oct 6, 2011

One thing I did that helped drive ability for my car was to switch over to the SN95 TB and sensors. My car idled smoother and ran so much better. Some say that throttle response is to sharp after the swap but since I run a BoPort 1.9 it made my car drive just as good if not better than stock never tested it on a stock engine, I did a write up on my swap if your interested http://www.stangnet.com/mustang-forums/816493-sn95-throttlebody-upgrade-wow.html , its not so expensive if you just do it yourself over buying one of those kits.

bonestock87 · Oct 17, 2011

Thanks for the reply guys, I've been busy and out of town lately. To update what is still going on:

Even after the plug wire replacement I'm still getting the part-throttle bucking. Again, this only happens at every other startup. I'm ruling out fuel and spark issues as it runs great until that dreaded time where it wants to do this. Once when it was having one of its "seizures", I shut the car down going down a big hill on the interstate and 30 seconds later put it back in 5th, let out on the clutch to refire it and the problem was gone for the rest of that drive. I can't explain this one. It's not bad gas as I've run 3 or 4 tanks through it from altering stations, I'm using 93 octane and I've ran some very good injector cleaner through it. Right now I'm thinking TPS, thoughts?

I know this isn't affecting this issue, but just as an FYI, my wastegate actuator is faulty and thus I'm getting all the boost the turbo can muster. I have a new one, just haven't had time to replace it. I'm controlling boost with my right foot for now. Oh, and yes vristang, I do still have the EGR junk connected and the computer is throwing no codes as tested with a very nice (borrowed) Snap-On Solice scan tool.

bonestock87 · Oct 27, 2011

In case someone finds this in a search down the road, my issue was fixed (so far, so good anyway) by replacing a bad wastegate actuator. It wasn't regulating boost at all. I also replaced the conical K&N filter with the factory air box and air filter just to get back to square one. It runs much smoother, pulls hard to the redline, and runs quieter even. My gillis boost valve is set right now to keep boost at 10lbs. I'll be turning up the wick 1 psi at a time until I hit the sweet spot between enough and too much boost.

cjk92turbo · Nov 1, 2011

was your car not accelerating right like you can only hold your foot so far on the pedal but if you gave it to much it would kick like in the back kind of like a shake? thats what mine is doing now

bonestock87 · Nov 7, 2011

was your car not accelerating right like you can only hold your foot so far on the pedal but if you gave it to much it would kick like in the back kind of like a shake? thats what mine is doing now

Exactly that. I still believe I have a slight TPS issue, but haven't checked it to see if I'm in the right voltage range.

mg man · Nov 7, 2011

Read a little on your swap. Like said check tps sweep. Usually easier with a needle type voltmeter look for dead spots in sweep. Also check the vam same deal. Also did you run a ground wire from turbo inlet to pin 49 on computer. Here is link if need for checking the 2 items I mention. Maurice
http://www.rothfam.com/svo/reference/sensors.pdf

bonestock87 · Nov 10, 2011

mg man, thanks for the link that's extremely good to have. I have not done checks on the tps or vam, I need to borrow an analog multimeter. I have acquired a large VAM and have an LA2 on the way next week, I'll install those to see if this issue goes away.

On the ground, I believe I have done that via running the orange wire that is on the turbo outlet to the ground wire in the O2 wiring that heads to pin 49. I may have explained that a little weird, but I did that just as Stinger's instructions say to.

mg man · Nov 10, 2011

Excellant only other thought. Make sure there is ground wire from intake to body. [I got this one and added one to main ground where battery cable attachs to body] Missing this does weird things. Maurice
Edit Note. This ground wire applies to turbo car and none turbo.

bonestock87 · Nov 17, 2011

Just a quick update. I checked my TPS voltage and sweeping voltage, its dead on perfect. I then put some new Motorcraft wires on this past weekend. 5 days of daily driving and the problem hasn't occured again. I bought a large VAM and an LA2 and hope to install them this weekend. We'll see how things go from there.

bonestock87 · Nov 19, 2011

Got the new stuff installed. Time will tell on the intermitten issue but I can definitely say the engine idles and runs a whole lot smoother than it did with the PC1 and small vane air meter.

bonestock87 · Nov 30, 2011

The problem has been getting worse. I've had to drive the 14mpg land yacht for a week now. No longer would it want to start and run good even when it was cold. After a lengthy discussion with a friend who is an ASE cert. mechanic and works almost exlusively on Fords, he believes my catalytic converter is causing my problems. Every sympton that it has he's been able to explain why the cat could cause it. I'm crossing my fingers. It all makes sense especially with a 26 year old cat that I've beat and banged on during the swap. Add to that the raw fuel it has seen while I've been trying to dial it in. He says raw fuel is the assasin of converters. So tonight if I can get it to run for a while I'm going to measure the exhaust temps before and after the cat. He says a bad cat will have exhaust temps LOWER on exit than entry. If it checks out, I'll be grabbing the sawzall and going at it!!

Time to go with a complete 3" system! Me: "honey I found out the problem with my car, it's the exhaust system, guess I'll just drive the truck for a few months until I can find the money to replace it". Her : "it'll cost you a fortune to drive that thing every day, just fix the stupid car and quit tearing up stuff that's not broke". Sound about right married guys?

bonestock87 · Dec 4, 2011

I removed the exhaust to see if maybe the cat was clogged. After a very loud drive around the country I brought it home. After 2 hours I went back out to start it and same issue! Didn't want to stay running. Crap! I have replaced nearly EVERY sensor except the MAP sensor. Just for kicks I replaced the stock 93 MAP with the BAP from the donor 86 turbo coupe. I reinstalled the exhaust. I'm now on day 3 of it not having any issues. I've been down this road before so I'm not getting too optimistic. My flashing check engine light even stayed off for several miles, but it has since come back. From what I've read, this indicates a severe misfire and/or severe emissions related problems and catalytic converter damage is likely. I don't want to tear anything up, but I'm not sure what else to do but drive it and see if the problem comes back. The only codes I'm getting now are for Vane Air Temp and Knock Sensor (which I have unplugged by design).

Anybody have experience with a check engine light that constantly flashes?

bonestock87 · Dec 16, 2011

A bad Vane Air Meter was my problem. No more CEL, runs great now!

79'293stang · Dec 17, 2011

Glad to hear you got it running well!

Part-throttle bucking and hesitation

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