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View Full Version : 04 Cobra cutting out at high RPMs after adding 2.80" pulley and computer chip


Cobra826
12-24-2005, 09:03 PM
I have an 04 Cobra with the K&N FIPK CAI, magnaflow mufflers and just installed a Kenne Bell Switch Chip yesterday and a 2.80 blower pulley and shorter belt. When I get on it in 2nd, it will run up to around 6k RPM, then flutter about like they do when they redline, then I shift to 3rd and run up to around 5k and that's where it does it in 3rd after running it hard in 2nd. It doesn't do it at a consistent RPM, but usually 5-5500 range in 3rd. I'm thinking it's not got enough fuel pressure or flow for that much boost and that I probably need Kenne Bell's Boost-a-pump. It runs very well up until it does this. I read on here last night in an old post where someone else was having similar problems on an 03 with a 2.80 and was having larger injectors installed as well as a boost-a-pump. Kenne Bell's research shows the stock cobra injectors will handle the load up to about 600 rwhp, but highly recommends a boost-a-pump on most applications. Anyone have any insight?

blk04cobra1
12-25-2005, 11:12 AM
You should be fine on your stock fuel system with just the 2.80 pulley...it's more than likely in your tune...im assuming you got a custom mail order tune, which arent bad, but you really need to get it on a dyno. Contact Pro-Dyno here on the board, he'll be able to help you out :thumbsup:

lorahcobra
12-26-2005, 03:35 PM
I agree with blk04cobra1 totally. We have the 2.8" pulley on ours with all the normal bolt-ons and no problems. :thumbsup:

Cobra826
12-26-2005, 07:26 PM
Thanks to you both for your replies. I contacted Pro-dyno who advised me to change and properly gap the plugs. Replaced plugs today with Autolite double plantinum 103s gapped .035. It had Motorcraft 22 series in it gapped between .048-.050. Didn't fix problem. It may have run a little stronger afterwards, but still fell on its face at high RPM and WOT. So, also replaced Fuel Rail Pressure Sensor and though maybe a bit better (not sure), problems still exists. If you don't hold it to the floor (WOT), RPM will run up much higher. In 2nd, it will run WOT up to around 6k before falling on its face, maybe a little over, but at WOT in 3rd, it's falling on its face between 4,500-5,000. While in 3rd and not at WOT, it will run up to 6k or more, but once over about 4,500 while doing this, the moment you go complete WOT, it falls on it's face. Though the tech at Kenne Bell I talked to when ordering their switch chip told me it would handle the 2.80 pulley and boost it creates, the instructions with the chip said you shouldn't exceed 11psi boost. Any ideas from anyone based on this updated info?

Big T
12-26-2005, 09:07 PM
If you have a 2.8 pulley, you probably have about 14-15 psi. I had a similar problem before and I found out my car was running rich. I got the tune adjusted and it is fine. I did change my spark plugs but I have a completely stock fuel system.

blk04cobra1
12-27-2005, 08:00 AM
I still think it's in your tune...only way to know for sure is to get a custom dyno tune...Pro-Dyno can help with this also, but you'll have to find a dyno local to you, then contact him while you're on it :thumbsup:

Big T
12-27-2005, 10:23 PM
I still think it's in your tune...only way to know for sure is to get a custom dyno tune...Pro-Dyno can help with this also, but you'll have to find a dyno local to you, then contact him while you're on it :thumbsup:


I agree :thumbsup:

Cobra826
12-28-2005, 04:41 AM
Got a fuel pressure tester today and drove it and at WOT, the pressure ranged from 70-100+ psi. Talked to Kenne Bell tech afterwards and we think it's probably burning way too rich at WOT, so he's gonna burn burn me a new chip and pay particular attention to my current problem and WOT settings. Should get it and know by weekend and will let you know. Thanks for trying to help fellas.

blk04cobra1
12-28-2005, 08:08 AM
I would think you want to be more in the 60-70psi range at WOT...good luck with it and let us know how it turns out :thumbsup:

Kix
01-15-2006, 03:13 PM
Am new to this forum and hope to get to know all u better, I was reading this thread and my car has the same problem but in 4th. I have a 04 cobra and the only mods are the sc pulley (not sure what size it is but it should be the same cause it gives me around 15psi) and it has the kenne bell switch chip. When I punch in on 1,2,3rd it goes up to 6rpms but when am on 4th it only goes up to 5rpms. But am not sure about your car but in my car it only does it once in a while. Cause I have taken the car up to 6rpms on 4th but thereís times when it only lets me go up to 5rpms. I have been trying to get it fix but they donít know what it is. If ur car gets fix I will appreciated if u tell me what u did to it. Thanks

Linn@Amazon
01-15-2006, 07:45 PM
sounds like a tuning issue..if you still have a problem after the reburn we would be happy to sort it out for you...

Cobra826
01-16-2006, 10:15 AM
Kix, and all others. Took the car to Strictly Performance in Houston last Thursday and they put it on their dyno, gave me a custom tune, and she runs like a champ throughout the power band now. The problem is in Kenne Bell's switch chip and as everyone says, there's nothing as good as a custom tune for your specific vehicle. The first run on the dyno was with the Kenne Bell chip installed. The car shut down (as is reflected on my printout) at 5,600 RPM. The A/F ratio was good with that chip, but their 23 degree advanced timing was a bit too much not to mention whatever is wrong in their program that causes it to prematurely shut down. With that chip, my max power was 424.3hp and max torque was 420.3. After the tune, max power was 450.6hp and torque 485.2. Timing now advances no more than 20 degrees and A/F ratio is about 11.8 from about 4k RPM on. This produced a tremendous HP and torque boost in the lower RPMs. In fact, at 3,400 RPM, it gained 100HP and 150lbs torq. On my tune, he programmed the new chip to keep my traction control turned off and though I'll never rev that high, he said he raised my rev limiter to 7K. These folks at Strictly Performance specialize on the mustang and all are previous Ford mechanics. While I was there, they were installing suspension components on one stang, a nitrous system on another, and doing something to a couple more, so they make many mods. Anyway, just wanted to report my problem is solved and it was in the tune (Kenne Bell chip).

AirForce1
01-16-2006, 11:21 AM
I agree with the guys. My car is running rich on a base tune to brake in my new motor. It does the exact same thing.

Your A/F is mostlikly 10:1 or below.

my Kenne Bell chip that came with my Blower is tuned to rich.

All Kenne Bell flip Chips are SCT so if you can find a shop that will tune SCT you can get it done right there where the dyno is.

The problem with pre tuned chips is they don't have the car to check the tune when they finish with the chip. They have to use average numbers from the enging code. The only problem with that is small adjustments have to be made that they cant do with out the car.

If it still does the same thing when you get the new chip I would just take it to a shop and have them dyno tune it. :thumbsup:

AirForce1
01-16-2006, 11:23 AM
Kix, and all others. Took the car to Strictly Performance in Houston last Thursday and they put it on their dyno, gave me a custom tune, and she runs like a champ throughout the power band now. The problem is in Kenne Bell's switch chip and as everyone says, there's nothing as good as a custom tune for your specific vehicle. The first run on the dyno was with the Kenne Bell chip installed. The car shut down (as is reflected on my printout) at 5,600 RPM. The A/F ratio was good with that chip, but their 23 degree advanced timing was a bit too much not to mention whatever is wrong in their program that causes it to prematurely shut down. With that chip, my max power was 424.3hp and max torque was 420.3. After the tune, max power was 450.6hp and torque 485.2. Timing now advances no more than 20 degrees and A/F ratio is about 11.8 from about 4k RPM on. This produced a tremendous HP and torque boost in the lower RPMs. In fact, at 3,400 RPM, it gained 100HP and 150lbs torq. On my tune, he programmed the new chip to keep my traction control turned off and though I'll never rev that high, he said he raised my rev limiter to 7K. These folks at Strictly Performance specialize on the mustang and all are previous Ford mechanics. While I was there, they were installing suspension components on one stang, a nitrous system on another, and doing something to a couple more, so they make many mods. Anyway, just wanted to report my problem is solved and it was in the tune (Kenne Bell chip).
Im glad you got your baby fixed.:thumbsup: :cool: