Problematic 03 Whipple 5 liter Cobra..

Trav4011 · Mar 10, 2007

My buddy just finished building his 03 Cobra.. Here's what he has installed..

5 liter built bottom end
stock heads
stock cams
Whipple kit with air/water cooler
2.8 upper/stock lower
60lb injectors
SCT2400 MAF
Modified stock pumps (not sure of the kit.. but it basically uses a larger diameter fuel hose and bridges the stock pumps with a larger Y fitting)

SCT tune copied from a running vehicle with the same injector/maf combo, just to get the car started to break in and dyno.

The car starts.. runs fine for about 5 minutes.. and then progressively gets worse as time goes on.. after 6-7 minutes.. the car is sputtering/backfiring, and won't stay running. Let the car sit for a day or so.. start it back up.. same thing.. runs fine for a few minutes.. then, starts running like crap.

All parts are brand new.. I've checked all of the obvious stuff.. ground wires, leaks, checked to make sure the MAF was getting 12 volts switched power. I'm not sure what else there is to check.. I'm thinking he's got a bad ECU, or MAF. The car would act up before he rebuilt it.. sometimes it would just start misfiring for a second or two..

Also, he is on his second lower pulley in about 10 minutes of run time.. He keeps sheering the pulley loose from the main shaft that screws into the harmonic balancer.

Odd stuff.. I'm not sure what else to try, except for a new ECU.. any suggestions?

thomas91169 · Mar 10, 2007

first thing that popped to my mind was a fuel issue. does he have a BAP or just whatever he did to the stock pumps.

maybe its a bad coil?

it could be the ecu, maybe find another cobra owner and swap them out and see how it runs before spending whatever ford rapes for a new one. then again, it could be a crap tune, no two cars are the same, that tune was prolly from a running 4.6 and now its a 5.0L and totally different VE charecteristics and powerband, you cant just cut and paste tunes.

btw he should have treated the problem before adding whatever he added, cause now those additions are going to hinder the process, and sounds like they have exacerbated the problem. so now you have to think, it was a 4.6 before and had a slight studder, now its a 5.0 and dies after minutes, the displacement grew and it went from a nosebleed to a severed limb, which leads me to believe there was a fuel issue before, and now its even more of an issue cause there is simply not enough of it, especially with whatever tune it has. im prolly wrong though, i am PUI'ing (Posting Under the Influence)

Trav4011 · Mar 10, 2007

Trust me.. if this was my car, I would have done things a lot differently.. I own a 500hp 2 valve, so I know how important it is to do it right the first time..

I suspect the ECU is bad.. I'm going to see if I can find one locally, and swap it out to see if it makes a difference..

Travis

Daggar · Mar 10, 2007

Time to go get the thing dyno-tuned. There are at least a hundred different things you can do to a tune to bring things into line to make a car run well. Who is to say that the approach used for the car that you guys copied the tune from, is the correct approach for the car that you copied to?

It was appearantly close enough to enable you to start the thing and get it going... GREAT! Now you're at least able to drive to a reputable tuner and have it tuned correctly.

You say that the thing start up and run good for a few minutes before going haywire. That's a pretty good indication that the MAF xfer function and fuel injector pulse and slopes are at least in the ball park. As soon as it goes closed loop, you start having having all kinds of problems. Could be any number of tables, settings, or scalers in the tune that are monkeying up the works. Cloning a custom tune from one vehicle to another is never a good idea... Not if you're expecting to run and tune and have everything be good to go anyway.

Saleen4971 · Mar 10, 2007

im with daggar. you really need a custom tune fomr scratch IMO.

is he using stock cobra pumps? with that combo i would think that he shoudl have duel focus or dual GT pumps, alogn with dual (and/or upgraded) FPDM's, upgraded wiring, etc.

Trav4011 · Mar 10, 2007

Again.. this isn't my car..

The idea was just to get the car at least in the ballpark so that it could be driven to the dyno, which is about 45 minutes away. If i had access to the SCT racer software, I could tune the car for him, and he would be on his way.

It's definately going pig rich when the ECU goes into closed loop.. I just wish I had access to the software, so that I could hook up a wideband, and at least get him in the ballpark for break-in and drive to the dyno. Looks like it'll have to be trailered to the dyno for now. I'm used to tuning Electromotive and FAST EFI systems on high horsepower Nissan engines, but, I'm not very familiar with ROM tuning factory Ford ECMs.

We fixed the lower pulley issue.. I screwed the new one together and TIG welded the crap out of it. I don't think it'll come apart again.

Travis

Problematic 03 Whipple 5 liter Cobra..

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