(sputter and stutter when cold if you try to hammer it) Help!!

[RichM1983]

I hate to post this thread but right now I'm kind of freaking out a bit. I just got my higher mileage Cobra and it has always ran great once warmed up. It will sputter and stutter when cold if you try to hammer it but once warm it runs flawlessly. Well this weekend I took it out and did a hard pull up to 3rd gear and was doing about 90 ish. When I slowed back down and shifted into 5th to cruise around it would stutter or miss bad. Car has a half tank of fuel so thats not the problem.....

If your in 1st or 2nd you really don't feel it...it doesn't really happen until until your in 3rd gear. Please tell me its something simple like the FRPS or I need new plugs and the motor isn't toasted.....It makes not ticks or knocks and idles great. It runs great in all gears if your not lugging or anything. Try to stab into into and it climbs in RPMS but just doesn't sound right.

Car has 124k miles

Mods: C&L aftermarket mass air meter, 2.8 upper supercharger pulley, cold air kit and Bassani exhaust



Please tell me its the plugs or something simple and that my motor isn't hurt....it idles to well and runs to well when not lugging to be something major right?

I wouldn't make a new post if I weren't panicking right now.

 

[RichM1983]

Also there is no CEL.

 

[Torch04RedSnake]

fuel filter? Do a compression check on the cylinders and check your plugs. It may need a tune up

 

[TRBO VNM]

you have to diagnose it. anyone smart will not just tell you it is fine and something simple.

Have you checked the FRPS? Have you searched to see how to check it? Have you pulled the plugs?

I would not be driving it without checking things out. you have some suggestions already posted.

 

[RichM1983]

I just went out and found a vacuum line disconnected from the FRPS and plugged it back in and drove it to see if it fixed it and it didn't. When I got back home I unplugged the FRPS connector and the idle would change and slow down. I would plug it back it and it would change and speed back up a little. Does that mean the FRPS is good?

 

[TRBO VNM]

did you smell in that vac line? do you have an aftermarket boost/vac gauge?

 

[RichM1983]

I did smell the vac line and it did not smell like gas....I do not have any aftermarket guages...

 

[RichM1983]

Also....the car builds boost just fine like before in 1st and 2nd...it almost seeems like a drive line issue in the clutch or tranny....could either of those cause an issue that would make it seem to hesitate at high rpm in the higher gears??

 

[TRBO VNM]

pull plugs and pull battery cable off prior to pulling plugs to help reset the computer.

 

[RichM1983]

I guess I'll pick up some new plugs tomorrow and then pull them on Thursday and check/replace....hopefully that fixes it....

Based on what happened when I unplugged the FRPS and the fact that I didn't smell gas in the vac lines does that mean the FRPS is probably not the problem?

Thanks!

 

[RichM1983]

Ok so I couldn't sleep. I got up and pulled the plugs and did a compression test. Plugs definitely look like they could be replaced. Hopefully that will fix my problem.

Compression test results:

Passenger Side Driver Side
Rear
160 140
165 155
155 145
170 140
Front

I know the passenger side is in good shape and the driver side isn't terrible but could be better, so I don't think that is my problem. Am I correct in assuming that those numbers wouldn't cause the symptoms I'm experiencing? I mean I would assume I'd be a little low on power but not near having any dramatic effect on running right?

I don't think that's bad for having 123k on the clock.

Also this was without adding any oil to the cylinder and a engine that wasn't hot but it had been ran in the past 2 hours.

 

[MoKo_03SVT]

start with the cheap stuff first. ie: plugs, fuel filter, etc.

put a new set of plugs in, and go from there.

 

[raym5_0]

+1 on new plugs....with more load on the car ( for ex in 3rd gear ) you will get the symptoms you mention with plugs quite often. I had a tuner tell me, he changes plugs on these cars at approx 3-5k miles, even if they look good.

 

[hotcobra03]

Ok so I couldn't sleep. I got up and pulled the plugs and did a compression test. Plugs definitely look like they could be replaced. Hopefully that will fix my problem.

Compression test results:

Passenger Side Driver Side
Rear
160 140
165 155
155 145
170 140
Front

I know the passenger side is in good shape and the driver side isn't terrible but could be better, so I don't think that is my problem. Am I correct in assuming that those numbers wouldn't cause the symptoms I'm experiencing? I mean I would assume I'd be a little low on power but not near having any dramatic effect on running right?

I don't think that's bad for having 123k on the clock.

Also this was without adding any oil to the cylinder and a engine that wasn't hot but it had been ran in the past 2 hours.

if i got those numbers when checking mine..id be :shrug:

mine has 311k on clock..180/190psi...

im on my 3rd driverside head,,rest of engine is original:??:

 

[Tims97SVT]

if i got those numbers when checking mine..id be :shrug:

mine has 311k on clock..180/190psi...

im on my 3rd driverside head,,rest of engine is original:??:

That's just awesome!

 

[RichM1983]

So is my compression teh problem. I don't think it would be. I know its not the best but its not so low it would have those symptoms right? Thanks

 

[hotcobra03]

its a good starting point...however it can go up(heads)or down(piston and rings)..

i would start over with test before jumping the gun,,,..bad test results/test done wrong can be costly

i never did a leakdown test,,but i think thats the next step that would help pinpoint problem...

 

[RichM1983]

Those compression test results are not wrong. I tested them all 2x. I also don't feel they are a cause for conern, BUT I need someone to tell me if they are based on experience. I know they aren't ideal but they are not what is responsible for my sudden change Correct??

 

[hotcobra03]

170 is your highest...your lowest allowed is 75%...or 128.5....140 is close...

you say you just got this car? how long have you had it?

 

[RichM1983]

I have had it since December 23rd. It has ran excellent and pulls extremely well until this happened. Car never had a hiccup and then all of sudden I do the pull up to 3rd and left and coast down to 55 and then shift to 5th and it makes this stutter, hesitation, shudder, kind of noice in all gears 3-6 and kind of in 1 and 2. I almost think its a clutch issue. Boost builds up in 1 and 2 and would in 3rd or higher if pushed but I don't want to push it.