Hesitation during acceleration... cannot figure it out.

[86LT1]

Car idles right where it should, can rev up with no problem not missing a beat.... now when i start driving down the road and gradually get on the gas my car dies dead on its face. Usually pretty abruptly, and its only for a second then it catches itself and is fine. This will happen in any gear. If I'm cruisin in 3rd and decide to start getting on the gas, boom it happens, same with 4th or 5th gear. And sometimes if im going through town it will do it when im pulling out of every traffic light.... then sometimes it wont do it at all.

BUT, if im sitting at a stand still and launch, going WOT through every gear the car doesnt flinch. Same as if im still at high rpms in 2nd and decide to hammer down on it.

So far I've pulled the O2s and cleaned them off, took out the MAF sensor cleaned that, and washed air filter... Tomorrow I think I'm going to stop at napa and grab a new TPS and see if that work?

Anyone have any idea on what this could be?

[popo8]

Throw a fp guage on there and watch it....paying special attention to the moment it stumbles...

[86LT1]

Yes! good idea, i'll try to get to that tomorrow before i buy a TPS.. do you think it could be flooding? or restricting? ... then depending on that I suppose it would lead me either to my fuel pressure reg. or a clogged fuel filter

[popo8]

Yes! good idea, i'll try to get to that tomorrow before i buy a TPS.. do you think it could be flooding? or restricting? ... then depending on that I suppose it would lead me either to my fuel pressure reg. or a clogged fuel filter

My vette (TPI car) was doing the same exact thing. I was losing fuel pressure when I "called" for it. Ended up being the filter for me.....

[OutCast]

Technical term for your problem is "tip in" I had this same problem and cured it by adjusting (not replacing) the TPS. Do you have an aftermarket throttle body on the car?

What are your IAC counts and TPS voltage at idle? IAC counts should be in the 30s and TPS voltage at .4 - .6 (mine was best at .45).

[86LT1]

Technical term for your problem is "tip in" I had this same problem and cured it by adjusting (not replacing) the TPS. Do you have an aftermarket throttle body on the car?

What are your IAC counts and TPS voltage at idle? IAC counts should be in the 30s and TPS voltage at .4 - .6 (mine was best at .45).

Yea, i have a BBK 58mm TB. How do you go about adjusting the TPS???? And i have no idea what my tps voltage is or my IAC counts? I do have access to a snap on diagnostic scanner which tells me a lot of information on my engine when running, but ive never looked at that stuff.

[OutCast]

Use the instructions in the link below but DO NOT perform STEP1 from those instructions. I don't know how big you motor is as far as cubic inches but there should be no need to open the throttle blades using the set screw. Start at STEP2 by opening up the mounting holes on the sensor to allow you to turn it a little once it's re-installed and find the correct voltage. My car is a 1993 and .46 was where mine ran optimally. Yours may be different as stated in these instructions. I found my optimal voltage by leaving the sensor just loose enough so that I could move it a little when the engine was running and "blipping" the throttle until I found the spot where the hesitation was no longer there. Once you find it, tighten down the mounting screws and go for a test ride.

http://www.golenengineservice.com/documents/LT1%20Tech%20Articles/Adj%20TPS.pdf

[86LT1]

Ok, so I'm gonna follow those instructions and I'm going to be looking for a .67v reading. Then adjust the TPS to the point where the engine will start and idle easily, once finding that point tighten down the TPS. And i should be ready to go??

I'm def gonna give this a go, the weather just got shitty again here in Pittsburgh, so hopefully i can find a nice day next week to try this out.
Thanks for the info OutCast!

[SeanMac]

imo, do adjust the throttle blades to get iac counts in line first on a warmed up car, then adjust tps.

[86LT1]

... i was reading through the instructions on how to perform this again, how do i find my IAC counts???

[86LT1]

How do I find out what my IAC counts are? then how do i adjust them, by re-positioning the TB?

[SeanMac]

with the scan tool, look in the datastream where it shows you what the pcm is seeing while the engine is running.

[86LT1]

nvm... i found out to get the IAC counts, and how to adjust them... i found this post while searching the internet, very helpful in understanding what to do along with what everyone has shared with me http://68lt1camaro.proboards.com/index.cgi?board=LT1&action=display&thread=169

But, is this my problem??? It seems the more i read about this issue, the more it relates to how the car idles, and not on fixing the problem im having ( sudden hesitation while accelerating ) But I just adjusted my TPS sensor to the correct voltage - .69-.71 and I'm gonna take it for a test drive tomorrow after work, while also checking fuel pressure on the test drive. And I'll post how everything goes.

[86LT1]

Well... went through all the rest of the steps today ( fuel filter, fuel pressure, & IAC )
seems like everything is right in line,except PSI, which I might adjust my fuel pressure a little after i figure out my hesitation problem
... at idle with the vacume hose off the pressure is at 43.5 - 44 PSI. But when i put the hose back it goes to 40PSI, and during driving hovers between 38-40 sometimes a little above 40 when i get on the gas, but dropping back down.... I have to do more research on this topic to see what i should be driving at/ idleing at. ( i have a holley adjustable reg.)

Since i went on a few test runs this evening it seems more and more to be an ignition issue rather than fuel or air. Tomorrow or Wednesday I plan on replacing ICM (stock) and if that doesnt work, onto the coil (MSD)

IMO i'm to the point where one of these has to be it, when i drive its like my car is hitting a dead spot ..... I DONT EVEN WANT TO THINK THAT ITS MY MSD OPTI-JUNK:censored:

[popo8]

Idle should be 43-44 if Im not mistaken....

[86LT1]

i dunno i'm at a loss.... i've like tried everything... i'm gonna go outside soon and try the ol' water spray over the plugs to see if I'm getting an arc anywhere but other than that i dont know.... except for the my f*cking $500 MSD opti

fuel filter-good ... TPS-good ... IAC-good ... fuel pressure-good ... plugs & wires- visually good ... changed out ICM-good ... changed out coil-good ...

i just drove for about a half hour, and the best way I can describe it is on a 0 to 100% acceleration, its like if I'm slowly accelerating at 25% get up to around 2500 rpms then get on a little more to about 50% acceleration and between 30-3500 rpms it like hits a dead spot, the car hesitates... like i just lost power, but then as quickly as it happens it picks right back up and goes back to normal. and this ONLY happens durring gradual acceleration. If I get on it, high RPM shifting winding out the gears.. never misses a beat. even when I drive it like at about 40-50% and let the car wind out at that without changing throttle position it also goes fine and doesnt hesitate.

Like i said at first... I DUNNO, i'm so frustrated. This did't happen til after I broke my car on the dyno at the end of summer last year.