Strange Hesitation Please Advise
 

Once my tank is about 1/2 full I get huge hesitation problems under heavy throttle. I fill my tank and the problems gone. I have already determined its not the gas.

Post more info:

Do RPM's matter?
Does it occur in turns and/or on straights?
Has it done as long as you've owned the car?
What mods if any do you have?
How is it at FULL throttle, heavy throttle, light throttle?

hesitation
 

Techno: Thanks for responding. If I accelerate smoothly it usually does not but if I punch it I eat the dash. It will accur in both staights and turns. I have every pfs bolt on including pms, hks twin power, taylor plug wires less than a year old and fairly new plugs. I am thinking fuel pressure, bad fuel pump or something.

Hmmm...I tend to agree with your assessment, you can test the fuel pressure, but I think you have to do it at the pump for a spec reading. Maybe a pressure check up front would at least indicate any anomoly.
Could be a problem with the secondaries...but I don't see how a full tank would affect them.
Wish I had more for you.

Hesitation
 

Thanks again, I will look into fuel pump diagnostics/replacement ect...In the mean time I will pretend I have 10 gallon fuel tank.

Hestation
 

Fritz Flynn, I am experiencing the SAME THING! and I have the exact same mods you do, except I have the PFS high flow fuel pump as well. What's funny is I took my car to PFS and had everything done there and then drove back to Chicago with a grin the whole time! And had none of what I describe as "sputtering" at WOT in 2nd and sometimes 3rd gear, it goes away if you back off the throttle even a little bit. My car is not a daily driver and I tend to really have fun with it when it is cooler in the evenings, say 60's or 70's. I have not talked to Peter Farrell yet but I am thinking that maybe I am running a little "Lean" even though the computer comes programmed pretty "Rich". I also run a downpipe and Highflow cat, both Bonez SS. I will call Peter Monday and inquire as to what his opinion is, I think this might be the answer. There is also a fuel cut at certain RPM's at certain boost levels which might cause this but I am told that when that occurs the car "falls on it's face" I don't know if that is what you are describing but mine is SPUTTERING at WOT.

Hesitation
 

BBeavers, Thanks for your input. I am falling on my face for sure but I don't think I am running lean cause shes backfiring. Again when I fill the tank its fine until my needle reaches the 1/2 way point then major hesitation definately like a fuel cut. If I keep it floored when the hesitation comes on I fall on my face then pop a wheelie but then I control my anger so I don't leave the rear axle in the road.
If I accelerate smoothly no hesitation. Its only when I stand on it and its much worse in 1st and 2nd gear.

Whatever you do, don't disregard this idea. A little bit ago I basically the same problem. Turned out to be the throttle position sensor (tps). If the wires or plug going into the tps get loose in any way, it will cause the problem. In my case, all I had to do was "jiggle" the wires around, test by accelerating, and continue the process until I found a smooth ride. I actually had to get something to hold the wires tightly in place because some bumps would loosed the wires again just a little and the problem would start back up. So if you know where your tps is, check the connection. Unplug it and plug it back in. Then drive around a little. If the problem continues, move the wires around a little and try again. I would at least check this first. It is a solution which will cost you nothing, but could be your answer. If you have any more questions feel free to ask.
Ricky

Just to throw out some ideas, i don';t know how much this will help.

I also have a PMC and one time, while making adjustments, i somehow set the max RPM to 4000. So as soon as i hit 4000, it was like hitting a brick wall.

On the other hand, if the problem always goes away on a full tank, then i would guess its your fuel pump. A lot of people who autocross run with a full tank becuase when 1/2 tank or less they have found hesitation in the turns. Have you checked your injector percentage on your computer. Rule of thumb is the pump is good for 85-90% - any more, time for a larger pump.

bbeavers - if you are experiencing a hesitation at high rpms, it is most likely a lean condiiton. depending on how your maps are set up, and a little to either your max boost or your PT settings.

anyway, hope this helps

Hesitation
 

Thanks for all your help guys. I think its the fuel pump but I will replug the tps just in case.

Ricky, where is the tps?

Silver93, thanks for your input. My problem only occurs above 4k or 5k rpm's so I think your right, I am also flowing more air due to the DP an high flow Cat. Does the crisp cool air, say 60-65 degrees exacerbate a lean conditiion? tthis problem only became apparent after a recent heat wave ended.

Fritz Flynn, the TPS is just behind the throttle body between it and the fire wall. look just above your oil filter. the workshop manual is not real clear as to it's location.

same thing after I had my new motor installed. After the break in period I had the turbos set to allow full boost, bu tI was getting hesitation.... it was a bad TPS. Clean it, move the connection a bit, and see what happens... GOOD LUCK

bbeavers -
yeah, i tell you, it would be easier if i knew the mods on your car.
i also think that there is a tendency to run the units TOO rich, which can also cause the hesitation.

finally today, i spent an hour doing runs and recording data and making adjustments all over the place and i'm finally getting strong smooth runs.

anyway, PM me

Silver93, My engine mods are posted on the sixth post on this page. Basically all the PFS mods plus Bonez downpipe and highflow cat, I also have the high flow fuel pump. Give me your thoughts. Thanks!

Fritz-
Sorry for the late post, but were you able to find the TPS? bbeavers gave a pretty good description of its location.

bbeavers -
this is my opinion of the GOLD box - (i have never used a purple, only the gold)!

i am convinced it takes time for the car to "learn" it's new settings. Remember you are using the PMC to trick the ECU.

ANYWAY, my original thoughts were that you were running lean, which you may very well be doing. BUT, and a very CAREFUL "but" - you could also be running too rich.

I originally installed my PMC with some general settings from the previous owner and the car drove like shit and backfired like crazy. Then someone told me to set all PT settings to zero, and only adjust the max boost settings on menu 6. This worked pretty good, and made sense, so i did and my low boost setting (10psi) ran well and the high (14psi) ran ok, until i got to 5000 rpm, then i would get hesitations. So, i would drive, make adjustments (while the engine was running) and try again, etc... This never solved the hesitation and actually, made the car run like shit again.

I became convinced of two things. Whoever said you can adjust this while the car is running is wrong (i think it screws everything up) and i was running TOO rich. I mean, the point of a computer is to add fuel so we dont blow up! RIGHT?! why buy a computer to only add like 6%?!? BUT,then why am i always backfiring and why is my tailpipe so damn blacK?!

Now, for everyone thinking, "hey dumbass, put it on a dyno w/ a wideband" - i say to you: "you are absolutely right! i agree" - i just haven't cause i don;t want to pay $100/hr for a sniffer. And yes, you are right that $100 is cheaper than $3000 for a new engine. So really, i have no response for that point, cause you are right!

Anyway, everyone told me backfiring was normal, etc....etc... - but i got tired of popping and smacking in parking lots all the time. So i started leaning things out a little at a time. I started by replacing the PT settings from zero to "-4". Then i started reducing the low and med PT settings more, and finding that the backfiring was getting less and less. This leaves me to where i am now. And yes, i also think these settings look crazy, BUT, except for the occassional 3K hesitation, the car is running much smoother and much stronger than ever before - and i have eliminated 99% of low throttle backfiring and 80% of backfiring during shifts .Also, my tailpipe is nowhere near as black as it used to be, but is now has a nice thin grey coating to it.

My settings are:
This is for high boost, 14psi (i set the PMC to a max of 15 psi). i don't have settings for low or med boost cause i never use it and always leave it on high. also, i use a profec B for boost control.


Idle: -28, +3 degrees

2200 4000 6000 7800
Low -22 -22 -20 -12
Med -22 -22 -20 -10
High -18 -16 -12 -4

Max Boost +6(-2deg) +8(-2deg) +18(-4deg) +20(-4deg)


you can see that only under high and above 6000 is there really any fuel added. At 6000 its +6 and at 7800 its +16. If you watch the readings, you;ll notice that your PT under boost is always on high.

This setup, based on the stock O2 sensor, gives reading in the .84-.88 (and some places .90).

Anyway, the car is running strong, no hesitations - which i had when the car was MUCH richer than this! if the hesitiation indicated a lean condition, i should have made the hesitation worse, not made things smoother!

Anyway, hope all this helps.

also, don;t forget, if you think you've been running rich, replace your plugs - as they will be fouled and will affect how your car drives under the new settings - i am running NGK BUR9EQPs all around

also, when was the last time you changed the fuel filter and checked the condition of your air filter-

both very important!

Hesitation
 

Ricky, Thanks for getting back to me. I replugged
the tps and still have the same problem however I talked to Peter at pfs and he thinks its the fuel pump. I don't have expierience fooling with gas tanks and such so I will let them fix it.

Silver93, Thanks for the great info, this should help a great deal since our mods are almost identical. My fuel and air filters were changed less than 3k miles ago. However, I am also running 9's all around for plugs but suspect even though they have less than 3k on them they may be fouled already based on your findings and theory about running rich. I am due for emissions testing before the end of the month and am considering going to all 7's just for the test, I have heard that hotter plugs = lower emissions. What do think? This is probably a good tome to try leaning things out anyway. Also, check out Cirani's "Lightning in a world of thunder" web site under engine how to's "Passing Emissions". There was a post by a Marc Schaefer that echos EXACTLY what you have said about the PMC and it's "Extremely" rich settings out of the box! Guess what? he leaned things out 18% on the PR-LL and PR-ML and it eliminated the "Popping" and hesitation. Check it out!

bbeavers -
yeah, i'll check steve site again for PMC info -
also, i don;t think you need to change to 7s on the plugs for emissions - i just did mine last month running all 9s, and the PMC was on the rich side (compared to now) and i passed so easily - it was a joke.

but i definately would get new plugs in - its makes a difference. and i keep and ID all my old ones - its a good way to do trend monitoring.

now, my problem is the damn 3K hesitation is showing its head again! argh!