extreme hesitation

22catch22 · Sep 12, 2008

I know this is for the big dogs but I figured there would be more knowledgeable/experienced people here and have not found the help I need in the v6 forums. Plus, as soon as I get this problem figured out I'll upgrade this engine. Have a 95 v6 automatic that has baffled every mechanic that has looked at it. Car has hesitation issues accompanied by spark knock and there is a total lack of hp. The worst part is after the car slows down (but doesn't come to a complete stop) and then tries to accelerate again. The car will not accelerate for anywhere between 5-25 seconds and then it will SLOWLY begin to increase speed. Transmission expert says it is not transmission, engine expert says it is a fuel starvation issue. Any ideas? Thanks for any help I can get.

WhiteFox342 · Sep 12, 2008

Install a temporary fuel pressure gauge that yyou can see while driving. Watch the gauge when the problem appears. If the pressure drops you may need a new fuel pump. This would be the easy repair.

If the hesitation occurs and the fuel pressure is good you will have a LOT more diagnostic work to do. Any number of things could cause this problem - a bad sensor like a MAF or ECT. It could be a wiring harness problem, a PCM problem...etc...

HISSIN50 · Sep 13, 2008

Are we to assume there are no codes present?

Have you viewed PIDs while driving?

Does it happen at all times or is it better when the engine is cold (for instance)?

Does it miss at all?

Has a compression test been done?

A little more info will help because otherwise we can only paint broad strokes.

Good luck.

22catch22 · Sep 13, 2008

WhiteFox342 said:
Install a temporary fuel pressure gauge that yyou can see while driving. Watch the gauge when the problem appears. If the pressure drops you may need a new fuel pump. This would be the easy repair.

If the hesitation occurs and the fuel pressure is good you will have a LOT more diagnostic work to do. Any number of things could cause this problem - a bad sensor like a MAF or ECT. It could be a wiring harness problem, a PCM problem...etc...

Thanks for the reply. My uncle told me to do the same thing. I will have to do this ASAP.

22catch22 · Sep 13, 2008

HISSIN50 said:
Are we to assume there are no codes present?

Have you viewed PIDs while driving?

Does it happen at all times or is it better when the engine is cold (for instance)?

Does it miss at all?

Has a compression test been done?

A little more info will help because otherwise we can only paint broad strokes.

Good luck.

Thanks for the reply. No codes have come on. The problems persist all of the time regardless of engine temperature. Any time I accelerate there is spark knock, but it is way worse when trying to accelerate right after slowing down. A compression test was completed and each cylinder was in the acceptable range.

22catch22 · Oct 2, 2008

Took my stang to another transmission specialist and he drove it around. In his opinion he thought that the transmission was working properly and that all of the problems the car is having is due to a computer issue. He thought that the computer might need a calibration update. Anyone ever heard of this?

HISSIN50 · Oct 3, 2008

Has anyone driven it while watching PIDs? This might capture a sensor or system that is out of calibration for the situation.

I'm not big into the OBD-II V6 EECs but generally recal's are for new mods or to fine tune little issues that come to be known from TSB's. This issue sounds like a sensor or hard part that is failing or otherwise out of whack.

An OBD-II car should spit a code with that kind of misfire occuring...........

toyman · Oct 3, 2008

Okay, I'm getting old and my memory isn't what it used to be, so what is a PID? I just know that when you tell us I'll say, of course, duh.

HISSIN50 · Oct 4, 2008

PIDs (Parameter Identification Numbers, IIRC) are just operating parameters viewed in real time. With a decent scanner (like an AutoXray 5K), you can hook it up and go for a test drive while watching or streaming most sensors and systems in real-time. This is useful when a car acts up during said test drive - you capture the data and review it to see what system was out of whack. The OBD-II cars provide much better feedback than our OBD-I V8 cars (most of this audience is OBD-I), so this should be even more helpful.

toyman · Oct 4, 2008

Okay. I never had an autoxray scanner just a code reader. However, with the AEM I can read/watch/datalog all the operating parameters. The trick of course is to have an idea of what it is that you want to focus on. IIRC there are over 500 operating parameters. For the OP it appears that he should focus on fuel, air and ignition related parameters. Sounds as if it's running lean from a stop or low speed.

Bosko5.0 · Oct 5, 2008

is the firing order correct???

94-302-vert · Oct 6, 2008

How about a good tune-up...

AP1995V6 · Oct 6, 2008

Do you have a humming sound coming from the transmission tunnel? It won't consistently be there, but it'll definitely come and go. It sort of sounds like the fuel pump. Just in the front of the car.

If this is the case, your transmission pump is on its way out. This is what's wrong with my car, and I have the same sort of hesitation. Everytime I completely stop the car, I have to wait for it to downshift then give it just a tiny bit of gas and wait for it to engage before I can go (usually a 10-15sec or so process). But this is just an excuse to upgrade to 3-pedals, but unfortunately, my engine swap is having to be put on stand-by .

Chythar · Oct 6, 2008

AP1995V6 said:
Do you have a humming sound coming from the transmission tunnel? It won't consistently be there, but it'll definitely come and go. It sort of sounds like the fuel pump. Just in the front of the car.

If this is the case, your transmission pump is on its way out. This is what's wrong with my car, and I have the same sort of hesitation. Every time I completely stop the car, I have to wait for it to downshift then give it just a tiny bit of gas and wait for it to engage before I can go (usually a 10-15sec or so process). But this is just an excuse to upgrade to 3-pedals, but unfortunately, my engine swap is having to be put on stand-by .

You could always find a wrecked GT/Cobra and upgrade that way. Take a look at my sig and check out my upgrade from a 94 V6 to a Cobra clone.

toyman · Oct 6, 2008

Chythar said:
You could always find a wrecked GT/Cobra and upgrade that way. Take a look at my sig and check out my upgrade from a 94 V6 to a Cobra clone.

Except the Cobra never came with an AOD-E.

Chythar · Oct 7, 2008

toyman said:
Except the Cobra never came with an AOD-E.

My comment was to AP1995V6, he wanted an "excuse to upgrade to 3-pedals" (auto-to-manual swap) and upgrade the V6 to a V8 as well. I can see where my comment would be confusing, considering the original post.

AP1995V6 · Oct 7, 2008

My 351 is only a short block so I'm thinking about getting rid of it and going with a supercharged 5.4 and using a t-56 transmission so that it can be a bit easier to drive than the beastly big bore engines

extreme hesitation

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