Hesitation issues

The hesitation issues comes and goes at different rpms. I really have no idea what could cause this. Basically when I'm driving at 65mph (2200rpms) the car bog's down and has a hard time moving. I've left it on cruise control and the car still has issues. It will slow down to 60mph then speed back up to 65. It does this alot. I have searched but cant find any problems with the car. I replaced the spark plugs. I also replaced my 02's (front) because the computer said they were bad. Then after all that the hesitation is still there. The computer inst throwing anymore codes either. The strange thing, When I'm driving at 55mph or at 75 (2500rpms) and over the car doesnt bog at all. The car drives smooth and stays that way. Anyone have any idea what the problem could be?

I have tons of mods. The basics are Vortech V2, 5.1L stroked engine, Cams, Heads, intake, throttle body, intercooler, fuel mods, and exhaust.

Could a bad IAC cause this?
What about a Bad Mass air? How could one even check that?
What about a bad TPS? Could that cause something like this?
Is there anything else I could check for that I havn't done yet?

syc_stang said:

im having this exact issue. my stang does it in all gears between 1500-2500 rpms and then fine after that( 5 spd).it acts like it has alot of back pressure in the exhaust and then when it open up its fine. im getting ready to look at mine. im gonna look at the plugs. specifically the plug closest to the thermostat. hopefully it wont be wet from coolant. maybe a fuel pump? im gonna check that too. also im gonna use some injector cleaner and see if that helps.

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Oh yeah I forgot to mention it happens in all gears as well. Speed doesnt matter its really the rpms. I have a free flowing exhaust with just 2 cats and I'm pushing 500rwhp and it was driving fine for 8 months after my tune. It wasnt untill a few months ago that its been acting up. I got a code for 02 sensors so I swapped them. Didnt fix it. I have two new fuel pumps in my tank so that couldnt cause the hesitation issues. I thought about a clogged fuel filter, but why would it work fine at 2500+rpms.

I've been thinking of pulling my mass air to see if it's dirty and needs to be clean. I really cant figure this out. I'm totally stumped. I even did the basics and reset the ecu. Let me know if you figure it out.

Do you also have a Vortech?

nyuk98gt said:

mat82284 and syc_stang:

Do you have access to a datalogger (SCT XCal plus a laptop)? You can replace a lot of parts and not find the solution so it may be better to datalog to see what is happening. (No flame intended - I'm trying to save you some money.)

Chris

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I do and can log it, but what should I be logging? I have the SCT livewire....

Nightfire said:

Bad COP's

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As for bad cops, how do I test each individual one? Shouldn't the ecu tell me when one goes bad??

trombonedemon said:

I just had to replace a bad COP today and all of the symptoms you've stated I had w/just one COP gone bad!

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Thanks guys for all the help. I've been busy so I havnt had time to respond.

Trombonedemon, How did you know which COP was bad? Did your ecu throw any codes or did you buy one and just swap it out one by one?

Thanks for everyone's help, but the fix wasn't anything anyone could have ever realized! Honestly I'm happy to have had this issue first. I almost bought a new set of COPS for my car too.

It started yesterday. The car was driving fine, then I go into the store come back out and no power at all on my car. I pull out my multimeter and it shows 12.35Volts but it was showing a negative sign like i mixed up the wires. I thought nothing of it. I unplugged the battery terminal and reinstalled it thinking a wire was loose. The car then starts, but as soon as I turned on the AC it died every time. (it was 98 outside so i needed ac) After 3 try's to get the AC to work the ecu shut off after my car surged and went into protect mode. I then disconnected all my stereo equipment (thinking a short happened) and proceeded to reset the battery again. This time the car had no power what so ever. I couldn't even set my alarm, or get the stereo to come on. I was mad and sat there for 15mins. Then I called my friend for a ride, but before leaving I was able to set my alarm. I then tried to start the car and it worked. I drove home, drove around down for a while testing the car and it was back to normal.

We'll this morning it ran perfect as well. It wasn't until 2pm when I got out of class I become stuck again. My car wouldn't unlock, or start. Not even a click. I called for a ride once again, then as im sitting in the car the power jumps back on. This time I started the car and it couldn't hold any kind of idle. I could hold it at 1500rpms 2000rpms or even 3-4000rpms but once i let off the gas the rpms fell straight to zero like a rock. I then tried over and over, and on the 5th try it finally idled. I then turned the AC on after idling for 10mins. The car surged and turned off again, but this time my friend was near the batter and said that a bolt of lightning shot out of the negative terminal. He was shocked, I was shocked and mad at the same time. I then took the battery out and took it back to kragen since it was under warranty. They tested it and it was fine. They then started to charge it and it started sparking again. At this point they just swapped it out. They told me that its like a 1 in a million chance but my battery was switching polarity. making the negative the positive and the positive the negative (which would explain my multimeter reading a negative since it does this when the wires are backwards).

After this the car runs perfect again. The hesitation is completely gone (so far) I've driven 20 miles and it never hesitated once. It used to do it every time on deceleration as well as cruising at 65. The car actually feels much better and more responsive now. The car was running with the hesitation for 4 months, I was hoping for a code but it never showed up. Now its fixed and I'm happy!

I've never heard of a battery doing that did anyone else know that it was even possible??? It sounds scary since it could have fried something in my car!

RedDaemon said:

Congrats everything is all better

How long have you had the battery before you started to experience your problems?

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We'll actually day 1 i had issues. I installed the battery in my car and after 2 days of my car sitting the battery completely died. After a recharge it worked great and didn't have any issues for a few months. i got the battery last December. It wasnt until march or so that i started having hesitation issues. I still cant believe the battery was the cause.

trombonedemon said:

Uhhhh, thats very scary; from what I read your battery could have exploded. Evidently the only way a car battery could have reveresed its polarity is that if the battery reached its full life cycle and someone reversed the leads when they recharged the battery. I wouldn't buy anthother battery from where you purchased this one at, b/c that would entail someone check the battery, realized it was dead, screwed up charging it, and put the battery back up on the shelf for someone to buy.
This is why we consumers need to check the battery date of manufacture before buying it.
Great problem and awsome job solving. This is exactly what this web site needs, queer situations like this one.

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Yeah im thankful nothing else broke. As for buying a battery elsewhere I would have except it was under warranty so i got a new one for free. This one works good though, I've been keeping an eye on it and checking voltage. I havnt had 1 issue like i was having before and my car drives so much smoother now.