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Discussion Starter #1
Took the car yesterday 11-9-12
Well I have been working on this car off and on most of the summer.
In short, I have a 97 Cobra 4V with a MMR1000, ported B heads, turbo cams and a MMR intake. I put the FF0n3 kit on with a turbonectics 78MM turbo. 80# FMS injectors and a BA5000 slot mass air. Every thing is new so I took it to the dyno to get it tuned. At first he could not get it to run under any load with out hesitation. After a while he got it worked out for the most part. He had to turn of the o2's.
The car is at 13# on springs. It would pull good, spool hard and fast about 3500 but when it hit 5,000 rpm it would start to break up. We ran out of time and he could not figure it out.
At that point it made 417RWH and 437F#T at 5,000 rpm with 16 deg of timing on a mustang dyno. Fuel PSI held at 52#'s when it hit boost with out dropping.
I changed the plugs from a TR7e reduced tip gaped at 20 to a TR6 standard gaped at 25, cleaned up all the coil grounds, replaced the coils. I don't think I have a motor to chasey ground. Just the bat to chasey.
Took it for a ride today. Drivability is good. Idle, From a start is good.It can pull hard in 1st 2nd, or even break spool it in second at a low speed and it pulls hard till 5,000. Pulls hard on the freeway, Just wont go much over 5,000 with out missing. No knock or miss codes. Not lean on the AME wide band. and Fuel PSI is good.
Other the the pass side pipe sitting right on the lower control arm every thing fits good. Im going to have to remove the pipe and notch it or dent it alot
I was thinking of pulling a cold side pipe and trying it out with no boost at all or trying a lower PSI to see what it dose. My goal it 20+ lbs. I think its in the tune. It pulls good just dies at the top.
I don't think it valve float. MMR did the heads and springs to go along with the cams.

I need to find a tuner that knows these cars.
What do you think?
 

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Sounds like it either the maf or ignition setup. I would unplug the maf and see if it will rev past 5000rpm without going into boost.
 

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What plug wires do you have on the car? And I assume you are using the stock coil packs on the car. Also what timing are you at right now?

The last time I had seen a problem like this was on a FAST setup, however, it turned out the plug wires were the culprit. Also, between a timing light and the ECU, the ECU would read about 6 degrees difference at the top, but as much as 15 degrees difference down low. Replaced with Magnacor wires and the hesitation went away, and the timing was dead on between the ECU and timing light.

I would also add a engine to chassis ground.
 

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Valve spring specs?
 

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Discussion Starter #7
Sounds like it either the maf or ignition setup. I would unplug the maf and see if it will rev past 5000rpm without going into boost.
Can I just un plug the mass, remove one of the cold side pipes to prevent boost and give it a try?
 

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Discussion Starter #8
What plug wires do you have on the car? And I assume you are using the stock coil packs on the car. Also what timing are you at right now?

The last time I had seen a problem like this was on a FAST setup, however, it turned out the plug wires were the culprit. Also, between a timing light and the ECU, the ECU would read about 6 degrees difference at the top, but as much as 15 degrees difference down low. Replaced with Magnacor wires and the hesitation went away, and the timing was dead on between the ECU and timing light.

I would also add a engine to chassis ground.
The wires are Ford racing 8mm, but they are a bit old. I should replace them.
The coils were MSD. I put the stock ones back on, removed the TR7 plugs, gaped at 0.020 and put in TR6's at 0.025 Timing is at 16deg
I will add a ground from the head to the fire wall.
 

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Discussion Starter #9
Valve spring specs?
Manley High Performance 4V spring kit (does not fit GT500) (Manley Part# 221434-32)
Recommended for all Forced induction applications and aftermarket camshafts, compatible with all factory locks and retainers. Up to .525 Lift 95lbs seat pressure/260 open pressure
100742

From MMR, instaled by them when they did the port and valve job.
 

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Seat pressures a little low
 

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You should have a two grounds from the engine to the chassis. My 97 had a large one and a much smaller one near where the K-member bolts up on the drivers side.


The car won't run right without these.
 

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Discussion Starter #15
You should have a two grounds from the engine to the chassis. My 97 had a large one and a much smaller one near where the K-member bolts up on the drivers side.


The car won't run right without these.
Thanks
I will add these also and give it a test.
 

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A good data log of events will shed light on what is going on with correct PID/DMR selected. I am assuming SCT software being used with tuning? If so you can download livelink from SCT website and log yourself with programmer.
 

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The wires are Ford racing 8mm, but they are a bit old. I should replace them.
The coils were MSD. I put the stock ones back on, removed the TR7 plugs, gaped at 0.020 and put in TR6's at 0.025 Timing is at 16deg
I will add a ground from the head to the fire wall.
sounds like the wires are your issue..

we had the EXACT same issue as you with my friend's car on Sunday.

after 20 passes or so...we swapped out the wires ..fixed any and all loose grounds and it made 3 clean passes back to back...
 

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Discussion Starter #19
It dosent feel like valve float. Could be.
 
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