Strange FAST problem...need help!!

[Windedv6]

I have a FAST problem That just surfaced. I don't own a GN but have been on the board for a while. The vehicle is a 93 Typhoon that is heavy modded. Bowtie block, billet crank, Flowtech ported heads, Pontiac intake with Wilson (ford type 75mm TB), 72GTQ turbo, 75# injectors, Digital 7 MSD, Race prepped fuel system, etc.

Truck runs 11.1s at 124 mph...

Problem....(just occured out of nowhere after three years of no trouble)

Under laod/boost the pulse width shuts down at 5,200 rpm no matter what gear it is in. Even in third I can run 23lb boost with everything fine till 5,200 rpm. It does not drop cyclinders like a rev limiter situtation, just fuel cut off .... but not completely.

Things that I did so far since trying to figure this out....

-Changed out double pumper for large external fuel system.
-unhooked 7 series MSD
-isolated boost controller
-change out TPS sensor (voltage is correct)
-timing is same (crank to computer)
-Changed out ingition module
-changed out 3 bar map sensor
-checked out wiring harness for grounds, etc
-checked alternator (14.4 volts)
-put in several older programs that didn't have this problem
-FAST sent me the a new box with 1.05 software

Things noticed.....

-When setting the rev limiter lower than 5,200, cyclinders drop as expected so I know the rev limiter works as normal.
-In park/netural (no load) the motor revs fine through 6,000rpms and above
-under load with little or no boost (5-8lbs) revs fine through 6,000 or higher.
- At 8-23lbs boost(or above)... shuts down, but not off, at 5,200 rpms
-tps still at wot (92%)when this happens
-timing stays according to table (24 to 26*)
- fuel pressure and boost fall back accordingly as pulse width drops
-data log shows that injector pulse width just drops (always at 5,200...no matter what gear)
-if I keep the pedal to the floor (wot and full TPS) it still runs smooth (at lower rpms), but fuel and boost are cut back and no power.
-if I let off pedal for just a second it resets and fuel and boost comes back...till it hits 5,200 again.

The new box and the old box act the same. Old box was tried in friend truck just fine.

I have had Speedpro/FAST for over three years with great success and (although not professing to be an expert), I have a good sense of the program. I have tuned my truck and several other vehicles with no problems over the years. Tony at FAST, Dave Henninger at Hardcore Motorsports (Formerly of Wheel to Wheel), and others are trying to help figure this out. So far we haven't.

Any ideas would be very appreciative. Maybe someone here has had this type of problem. Hopfully it may be something simple...something that is so obvious it is just passed over as we may be making this to complicated.

List of Mods


Sorry about the long thread.

I am traveling on business till Tuesday. I can post a run then if needed.

Thanks to everyone in advance....

John

 

[norbs]

This sounds crazy, but i think its the valvesprings.

 

[Windedv6]

I will definately take all ideas into consideration. This is a healthy build and the problem started all at once. I normally run 28-30lbs of boost at the track with no problems. 22 to 23lbs on the street. This happened from one day to the next. Approximately 2,500 miles on motor.

Also it does it's shutdown exactly at 5,200 rpms everytime, even at different variables to boost, timing, etc. I even changed the a/f ratio and settings to see if it would shut dowm at a different rpm. Always 5,200 rpm..... I wouldn't think avalve problem would act as consistant.

I keep going back to the idea that there is an isolated low voltage signal feeding info into the computer.....but can't find anything. Overall voltage is at 14.2 -14v.

Thanks'

John

 

[bobc455]

I'm thinking valvesprings also. Do you know what spring pressures you have?

Is it possible that there is some sort of damage (broken dampeners in the springs, etc.)?

How big is your camshaft?

-Bob Cunningham

 

[tonydee64]

Originally posted by bobc455
I'm thinking valvesprings also. Do you know what spring pressures you have?

Is it possible that there is some sort of damage (broken dampeners in the springs, etc.)?

How big is your camshaft?

-Bob Cunningham

I can't remember what all you listed that you have tried. Have you had your injectors flowed lately? (maybe they need cleaned). You may have one or more bent pushrods, 3) Check the cam lobes with a dial indicator (I once had this happen to me) in a manner like degreeing the cam. Bad coil pac? I don't think it's your FAST box. Failing DIS sensor? Plug wires?

 

[Lonnie]

Check the air filter.

As simple as it sounds, after a few miles they get a slight restriction (from dirt) & will collapse shutting off the air.
I have had 3 experiences with this on different vehicles.

Let me know if it works.

 

[Windedv6]

The cam is a Comp roller 09-412-8. the specs are; .500/.500 lift, 260 duration, 112* lobe separation... rockers are 1.5 ratio. Nothing radical here.

Comp Cams Valve springs #985...double spring, rate 333.
Valves springs, dampers show no damage. Also no change in valve lash has occured. I'll do some futher testing on the valve train.

I would not think that valve springs would wipe out all at once and how would it relate to a shut down at exactly 5,200 rpm every time, no matter where the boost is set above the 8-10lb range?

I am having my alternator tested tomorrow even thought my voltage shows a steady 14.2v and am trying a different dist.

We tried it without the filter.
tried other coil
tried other ignition box
new wires
new plugs
new cap
new rotor

Same song.

John

 

[RickWI]

BAsed on experience three things I would verify, inspect and or replace if needed.
Fuel filter(s)
Fuel pump
Fuel pickup
Fuel flow

 

[Windedv6]

Thanks Rick,

Going through this for the past month I replaced the......

-two year old walbro 340 double pumper with an external Aeromotive A1000.

-the stock filter with 2 filters. A high flow 100 micron pre-pump filter and a 60 micron post pump filter.

-the stock metal lines -10 for the supply and -8 return.

The tank has been sumped and until I find the answer to this porblem I have been keeping a 3/4 to full tank of fuel.

I am running a 10 gauge wire for the pump with a 30amp relay.

Pressure is consistant with a 1:1 ratio with boost rise.

This system change made no difference the the 5,200 rpm shut down. Same as with the old system.....except the $1,000 price tag.

John

 

[Windedv6]

I may have solved my problem. I had my alternator checked out and one of the springs that held the brushes in place was broken. although it was hanging in there at 14-14.2v the ampere was falling off under load. It's a 180 amp alternator. And I am running electric fans, water pump big fuel pump and 75# injectors.

The alternator fix didn't do all the solving, but moved the 5,200 cut off to the 5,400 range. This prompted a further look at the possibly of the injector driver overheating, in which FAST will shut down. I was told that the marine application for FAST was having the same problem because of the extended WOT service.

Dave Henninger came up with some tests as well as solutions to help out the injector driver form overheating. It helped. So, hopefully, to stay away from this problem I went from 75# injectors running at 80% dc to 84# injectors.

The biggest help will be taking my base fp setting from 40# to 45#. These two changes should allow the injectors to do their job with less power draw.... thus less heat on the driver.

I made several runs this evening and everything held fine. Now back to all the fine tuning.

I am so hoping that I don't have to come back with the news that it's still shuts down. This as been a nightmare for several weeks.

For what's it's worth I was told the BS3 will not have this problem as it as a different style driver setup. I think I am headed that way.

Thank's everyone for the ideas and support....

John

 

[norbs]

Are you sure its the drivers, no one else has run into this problem that i know of. Please update us on the outcome.

 

[Otto J]

Just out of curiosty what are your plugs gapped at?

 

[Windedv6]

Plugs are gapped at 32.....never had any high boost misfires since I went to the digital 7 box last year.

John

 

[gnsrule]

Any updates ??

 

[Windedv6]

Everything is fine....in fact yesterday I bumped into the 10 sec range for the first time... Barely, if you call a 10.984 running tens. None the less I will take it. This is the first that I have been to the track since May. I spent most of the summer chasing down the "shut down ghost".

Full slip...

1.56 - 60 foot
7.07 - 1/8 mile
10.98 - 1/4 mile
128.4 - mph

Some tuning data...

AFR Target - 11.8 @wot
Timing - 24*@wot
Boost - 22#
Fuel - 104 Octane

Hopefully I can improve on this as I tighten up the tuning. With my old Stealth 70 turbo I was running 28# of boost with 26* of timing and 12.4 AFR. I was using 110 octane and running 11.1s in the 1/4 at 124 mph.

This truck weights also in at 3,760lbs plus driver.....I think a diet is in order over the winter.

As an update on the past problem....I made the changes in the previous thread and the problem went away. Thanks for asking.

John

 

[bobc455]

Your fan should automatically shut off at WOT...

What is your TPS reading at WOT? Or, is your fan not controled by your FAST?

-Bob Cunningham

 

[norbs]

When the fan shuts off at wot down the track the car actually goes slower with no fan than with the fan on. I dont like that on the fast.........

 

[Windedv6]

I do not run my fans through the FAST program. Actually you need the blades spinning or they become a restriction.

John