Cobra hesitating at 1500-2100 rpm?

[stang8762]

My cobra has a slight hesitation/bucking at 1500-2100 rpm at part throttle. I had the problem for a while and i figured i would just deal w/ it b/c i was adding a turbo .. Now that i added the turbo and a assortment of parts its still there even after it was tuned. Its real bad when the car isnt up to temp . I have since brought it to my tuner and we took it down the road so he could road tune it .. He felt the hesitation but he said everything looks good as far as numbers ( mass air function , o2 and so on). He added a little fuel at the hesitation rpm and told me to drive it around but its still there, only now the hesitation is at about 1800-2200. He also said it could be mechanical or a charecteristic of the car. Before i take it back to the tuner does anyone have any ideas?

Again the hesitation was there before the turbo kit, new parts, new motor, tune and parts listed below so im thinking its somthing other than the tune.

I have added new:

Forged motor
70mm turbo 6psi 455hp
03/04 tank and pumps
HPX mass air blow through
60lb injectors
fuel filter
Tr6 plugs gapped at .030

 

[01bluesnake]

One thing to do when you have issue, is never replace parts expecting a fix, without diagnosing what the original problem is. Can you do a run down of what the car had done to it, when you first where getting the issue, maf, injectors, tune, ect. Also do you have a wide band on the car? Thanks.

 

[99cobra09]

check your plugs my car was doing the same thing, i tried everything and i redid my plugs to NGK and it fixed my hesitation.

 

[stang8762]

One thing to do when you have issue, is never replace parts expecting a fix, without diagnosing what the original problem is. Can you do a run down of what the car had done to it, when you first where getting the issue, maf, injectors, tune, ect. Also do you have a wide band on the car? Thanks.

Yeah i figured it was just a bad pump or injector ..Origionally the car was stock and i had a JLT intake, Mac exhaust , 3/8 intake spacer and a Amazon email tune and the car would hesitate a little when it was cold. The only part thats left still on the car is the 3/8 intake spacer.

I do have a Wideband and air/fuel numbers are 13.8-14.7 even when its hesitating . My tuner told me all the numbers looked good.

check your plugs my car was doing the same thing, i tried everything and i redid my plugs to NGK and it fixed my hesitation.

Yeah the plugs were new before the motor install but im going to check them again maybe get some new ones and re-gap the plugs

 

[01bluesnake]

Yeah i figured it was just a bad pump or injector ..Origionally the car was stock and had a JLT intake, Mac exhaust , 3/8 intake spacer and a Amazon email tune and the car would hesitate a little when it was cold.

I do have a Wideband and air/fuel numbers are 13.8-14.7 even when its hesitating . My tuner told me all the numbers looked good.



Yeah the plugs were new before the motor install but im going to check them again maybe get some new ones and re-gap the plugs

Ok, can you log your throttle position sensor voltage, while it is doing this? Thinking it may be a dead spot in the tps.

 

[stang8762]

Ok, can you log your throttle position sensor voltage, while it is doing this? Thinking it may be a dead spot in the tps.

I will check to see if i can log my TPS on my sct program ..

 

[stang8762]

Still working on this hopefully this weekend i can datalog my tps ..

 

[stang8762]

update:

While looking over the car i noticed the DPFE sensor on the back of the intake used for the EGR valve, one of the vacuum lines blew off so i put it back on and under boost it must have blown off again so i hose clamped it .. It solved 75% of the problem. There is still a little hesitation so maybe my egr valve could be bad . It make sense since i think the egr only works at part throttle around the rpm range that i was having issues.

I also changed my plugs w/ a new set of TR6 plugs and gapped them at .030. Ive read in some posts on the terminator forums that some cobras dont like the TR6 plugs and to switch to TR6ix (irridium) or autolite 103.

 

[stang8762]

Still working on this problem .. disconnected the DPFE Sensor and it went away .. or so i thought.. Took it to my tuner again and he says most of the stuff he can check such as the mass air is fine .. Still no codes or anything .. Might just try to change the TPS and Idle Air Control valve since now i have a slight hunting idle when i come to a stop ..

 

[01yellercobra]

Have your tuner turn off the EGR in a tune and try that. I have a low speed bucking in mine that's because of the EGR. I've replaced the valve and it didn't fix anything. I'm sure it's the piece on the back of the intake. But I have the EGR turned off and the car drives fine.

 

[olgreydog7]

I am actually having a similar problem too. Same thing, slight hesitation around 1500-2000 rpm and then it smooths out and the power comes back on. It only does it at part throttle. It gets better if I use Lucas Oil octane boost, the stuff that says not street legal. I figured it might be in the timing, but my numbers all look good too. My plugs are also TR6s and they looked good when I pulled them this weekend. My EGR is deleted and turned off in the tune.

 

[stang8762]

UPDATE:

http://www.svtperformance.com/forums/engine-tuning-214/718422-tr6-plug-issue.html

Even though i had new NGK TR6 plugs i saw another thread on here about swapping to a non-copper plug so last night i switched to the TR6xi iridium plugs gapped at .030 and it solved the hesitation while driving . The only time it hesistates is when i let the car sit for 20 min or more or when its cold and i come out in the morning and just try to get in it and drive .

It will do it also after driving, Even though its warmed up, and i turn the car off and let it sit for 15 min. I just cant get in it and drive it or the hesitation is there have to let it idle for about 5-10min then good to go ..


It always happens about 1700-2100 rpm after letting the car sit not running.. I watched my wide band and when i give it part throttle at 1700-2100 rpm after siting the wideband goes lean and wont read when usually at 14.7 air/fuel.. After sitting idling its normal with no hesitation and AF is perfect...

Can it be a lazy o2 ? or timing or fuel , change spark plug gap ?

 

[3B99SVT]

Have you cleaned your IAC yet? I get a slight hesitation when cold at part throttle and if I clean the IAC it goes away for a while.

 

[stang8762]

Yeah the IAC was cleaned 2 days ago .. I get a slight hunting idle between 700-1000 rpm so maybe the iac is going .. I planned on getting a new one anyways ..

 

[Black*Death]

I will throw O2 sensors into the mix. I know no codes, but if they are not working perfectly may cause the issue?

 

[olgreydog7]

I have less than 5000 miles on new Bosch O2 sensors. I don't think that is the problem with mine, but it is always a possibility. I still need to datalog and see if I can see anything at all.

 

[nasty99]

yo dude mine just started doing this yesterday, and i just got it back from the shop. he fixed my exhaust leak and put my old clutch back in but then i just started getting this hesitation yesterday. idk what it is

 

[stang8762]

So far i have :

-Disconnected the DPFE Sensor ,( it helped at first then the hesitation came back .)

-Changed From Ngk Copper TR6 plugs to Iridium TR6xi plugs ( got rid of 90% of the prob)

-As for the hunting idle i re-loaded my tune and it fixed that..

But i Still have things to try.. I dont think its just one thing .

 

[nasty99]

so should mine go away if i change out my plugs? cuz when i gas it, its starts bucking and stuttering.

 

[guilly55]

Just an idea but when I had my 95 cobra it hesitated because the converters were clogged. Not sure if your running off road or not.