TAC

I still have my "fuel starvation" problem. I have another clue that may add some insight. The symptoms are that at a certain point in time, the car refuses to accelerate properly. It acts like it's out of gas. The symptom occurs in boost and not in boost. The first time it showed up this time I simply pulled away from a stoplight going around a left turn. The engine hesitated for a brief second and then continued. I was not "getting on it" and it happened when I shifted to second and continued to accelerate at a very moderate pace.

I immediately went back on the highway and started testing. If I punch it, I get the bucking. If I accelerate a little slower, I get sputtering and hesitation. This all took place with the tank showing 2 bars below 1/2. I went to a Chevron and filled up. It took 12 gallons...about what it should be. The tank appears dead on capacity wise. The problem continued with a full tank...no real difference. The boost guage never gets above 50" cause I shut it down as soon as I notice the problem and the problem shows up well before the turbos get completely spooled up.

The new clue is that the problem appears to be heat/time related. Very similar to old vapor lock problems. I recently replaced the fuel pump hoping that would fix it. I never saw the problem again because I never drove it for that long of a time period. This time I had been driving on the highway for 2-3 hours before the problem showed up. I let the car sit for 3 hours and went back out and the problem was still there. I let the car sit for 24 hours and went back out and no problem whatsoever. I can rip through the gears with impunity. I drove and tested for 1/2 hour tonight and could not get the symptoms again. The boost guage looks very steady and pegs at 52" while floored when not exhibiting the above symptoms.

I am really hoping this rings a bell with someone. I can think of lots of things such as:

vapor lock?
pressure in the gas tank?
ignition problem-component failing at high temps?

All suggestions are appreciated. I hate taking this to the shop without a good idea of what's wrong but I don't have much choice. It appears something is failing when hot. Please help.

1 issue that I don't think is related but I'll toss it in. My throttle is sticking slightly...the revs stay up when I shift. Kind of like a stuck choke-a very light tap on the gas pedal always drops it back down. This happened once before last year and a very thorough spraying of the linkage and spring with carb cleaner eliminated the problem and it appears I've eliminated it again for the time being. With the engine off the spring seems very solid and returns the linkage to the stop with no hesitation so I don't know why it sticks with the engine running. Is my cure the accepted method for this or am I masking something like a bad throttle position sensor or ???? Could this be related to the above issue?

Thanks for all help.

Ultra Slow

If your tank it 100% full, you should not have a problem like this. These cars, depending on individual cars power, will starve anywhere between 1/2 a tank and lower. Mine does it right at 1/2 a tank at lower speeds. All the gas is thrown back from the hard acceleration, and the aftermarket high volume bosch pump callaway sticks in the car cant pick it up and causes that problem that can be very destructive... Notice the word "aftermarket" and "problem" always go hand in hand. Check any aftermarket or mod stuff first as that is usually the problem. If you are certain, without a shadow of a doubt, your fuel pump is mounted in the car RIGHT and the leads are not lose and throwing sparks in your gas tank, the try these things;

Your car is not vapor locking. These just do not do that.

First, check your fuel pressure... You must take the front injector(s) hose off the shrader valve and check it just like a TPI.. Should be about 48 at idle with the vac/pressure line undone. If not, your pump may be the wrong one, or that little FPR is bad... If you change, be sure to get an adjustable.. If you boost your car, you want to raise it up to the low 50's anyway.

Second, make sure there is not some wierd problem with your fuel pressure relay coming loose or kicking on and off. You can pull the relay and jumper the hot side and keep the pump on all the time and test this theory.

Third, and probably unlikely. I have seen a couple c4s in my time that have
been jacked up by "billy bob" mechanics that have put a cradel jack in the right rear secrion of the car before the tire and crushed the metal supply and/or return line with the jack. The car idles fine and runs fine at low speeds, but at high fuel requrements, its like a low fuel/vapor lock scenario.


Fourth, I'm sure you changed the fuel filter, but make sure the callaway built heat shield is over the filter. This "might" cause a problem from heat soak/vapor lock if they left it off. Many flat rater shops discard it as BS heat shield part.

Fifth, Check the microfueler computer under the driver side kick pannel. Make sure it is not coming lose and causing an intermidant problem with the secondary injectors kicking on and off. Also make sure the boost/static vaccum line is hooked good and will and has not blown off under boost. Check it ALL the way to the intake where it hoods under the TPI byt the FPR. This is aftermarket and it usually causes lots of problems.

Sixth, Go back through any maintenace the car has had in its life. If you took the car somewhere, more than likely whatever was done concerning any of the special areas of the car (turbos, injectors, etc) was not done right and usually causes more damage than good to the car. Most callaways I have seen suffer hard from this and thats why the car gets a bad rap and is not known for being fast.

Hope this helps.

Also, if you replaced your pump, I hope you went back to the same bosch pump as callaway had. If you put a stock l98 one in, thats your problem.


One other thing. Check ALL the hoses going to your throttle body, especially those from th carbon canister... They are usually big holes in them and big boost leaks too.



[Modified by Ultra Slow, 1:36 AM 4/30/2002]

TAC

These are some great tips, I'll print them off as a checklist. As far as the pump goes, yes I bought a direct replacement from Callaway. I can't be ABSOLUTELY positive about the installation but am fairly confident it was done right. The shop I go to is a known local speed shop that has specializes in vettes and Mustangs. They even had one of the Speedvision mustangs to setup a few months ago. They work on a Ling TT here and have a good word of mouth reputation. They correctly diagnosed and replaced a bad wastegate last year. Yes, I had my current problem before it ever went to this shop so they didn't cause it. I just figured it was the problem with having a low tank that Callaway refers to in their addendum to the owner manual.

Yes, the fuel filter was changed last year and I will probably do it again to be sure. Are you saying there is a heat shield on the inline filter that's under the car...under the x-frame? I haven't been under there for a while but don't remember any heat shield. It seems kind of far back for that...or perhaps it can get hot from the exhaust pipes?

As for the fuel starvation under 1/2 tank the last time it did this filling up the tank didn't have much of an effect, if at all. After 24 hours of cooling the car ran fine. When the problem first occurs does it leave a residual effect that has to work it's way out of the system or something? I'm thinking of testing by driving a long time to heat it up but fill the tank every hour or so to keep it fairly full. If the problem shows up initially at 3/4 full or fuller, it probably isn't the fuel pickup problem. If the problem never shows up when keeping the tank full I think that eliminates everything BUT the fuel pickup issue. Remember, the first time I noticed the problem this time was under very sedate acceleration. If that's enough to cause problems ... :nonod: Also, when I first got the new fuel pump I went out and tested with only 2 bars of fuel left and didn't have any problems at all. I didn't run it for 3 hours...just long enough to note it didn't act up with that low of fuel.





[Modified by TAC, 6:49 AM 4/30/2002]

Stan A

Ultra gave you a great list to work from. Go with it!

I know we talked about the bladder tank liner and I believe that you checked it out, However, we have also seen a condition where the liner will move in such a way that it can block the gas and re-settle into position like there is nothing wrong when checked by eye site. You really need to be sure that the bladder is not loose.

Good luck,
Stan :chevy :seeya

ZR1

Just curious, but did you check the fuel pump? I know you said you had it replaced but I just worked on a problem like this and the line attaching the pump was not connected properly. It gave the same results.

Airborne

Tim,

I would re-check everything you did such as pump, filter, fuel pressure, and especially Ultra's "crushed line" idea.

Have you looked in the tank to see if any contamination is present?


[Modified by Airborne, 9:48 PM 4/30/2002]