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Sudden power loss at 5000 rpm. Got me stuffed... 

 

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 Post subject: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Thu Jan 27, 2011 10:23 pm 
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My problem is when I’m wide open throttle, I get to 5000 rpm, and the car stops accelerating and drops back to a constant 3600 rpm, not accelerating or decelerating, just hangs on at around 3600rpm, until I get my foot off the accelerator.

I had 13 psi boost with a powerdyne BD11A and a billet impeller, now have an XB1A after the BD failed, so boost should still be around that pressure, will check the boost soon for a more accurate number.

I have a good air fuel ratio, with an adjustable FPR and a wide band to check.
I have a MSD 6AL ignition with cold plugs gapped to 30 thou.
I have a Turbosmart bypass valve, and have tried a strong spring on the hardest setting to eliminate boost leak from the valve.
My heads have edelbrock factory springs running a crane 2031 cam with 1.72 rockers, which I would think would be ok for boost.
My ACT sensor resistance reads correct, as does the voltage to it.
My engine doesn’t miss fire so I wouldn’t think it would be the leads or ignition.
I doubt it would be the blower seal as I get good acceleration until 5k.

My mods are in my signature below, and haven’t changed anything to cause this fault, it has just come on, but for the life of me I can’t figure it out.

I’m thinking this is ‘Limp home mode’ related possibly to the trans 2500 rpm stall.
It does feel like a heap of timing is suddenly pulled until I pedal the accelerator.

I’m going to pull the EEC codes when I get a chance, do a compression test and gap the plugs to 25 thou in case of spark blow out.
If this doesn't work i will lower the boost to see what happens.
Might also check the trans fluid and may visit the trans doctor for a check up.

Thanks for reading,
Any thoughts...?

 

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ED Fairmont Ghia.
306ci, Pro-m 80 MAF & #42inj, Kirban AFPR, Walbro 255LPH intank & inline, BBK 70mm, Ported Edelbrock #60399, Ported Explorer, Crane 2031 & YT1.72, MSD 6AL, paciemaker tri-y, 2.5" cats into single 3". H/D stall. 3.45 lsd, Powerdyne XB1A.

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 12:12 am 
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At a glance....
6AL problem, 3600rpm is approx the switchover point from MSD to single spark.
Stock Edelbrock springs are generally only suited to flat tappet cams...doesn't explain the drop back to 3600 though.
Fuel pump and or filter or some kind of restriction in the fuel system...you didn't mention whether the AF changed significantly at that point?
All of the above doesn't really gell with your TPS posi having an affect though. 2500 is right on the point where a stall can cause limp mode but coming off the throttle and returning to normal drive doesn't suggest that.
Check you haven't got a snapped throttle shaft. I've seen this where the blade gets blown shut even though the TPS shows WOT...maybe not all the way shut in your case?. Early BBK t-bodies and some others where they used ground away shafts rather than slit through for the blade tend to snap at one end.

btw...good move on the blower. Any belt driven centrifugal is a joke blower in my book and it seems even Powerdyne thought the same :mrgreen:
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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 1:58 am 
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I will check the Throttle but it is the one with the blade through the shaft, and would seem unlikley to give these consistantly repeated results im having if the shaft is damaged.
The heads are 'performer 5.0' so I would think there springs would suit rollers, and boost wouldnt be mre than 18psi as thats the max for the XB1A anyway.

It doesn't seem to make a difference what my air fuel ratios are, as i can wind the pressure up until it goes rich off the WB scale well before 5k, or have it where it is now, at 11.3:1 when it dies off at the 5000rpm mark.
When the car dies off at 5k its not harsh, just dies, like timiing is being pulled(similar to reaching the MSD soft touch rev limiter), then with the boot still in, the revs drop to 3600, slowly climbing to 3800 with an af ratio of high 13:1, as it probably would with no load.

Im wondering if with extra boost the stall speed has gone up, and the engines EEC isnt liking it, pulling timing on the transmissions behalf?

Im startng to think it is the MSD, I may see if i can bipass it and give that a try.
It wasnt a new MSD when I got it, so its probably had its life. A bugger to get to though, its mounted behind the dash.

BTW the BD11a made me 274 rwkw at 13psi before it basically melted, but i kinda knew it would eventually, just couldnt help myself.

 

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ED Fairmont Ghia.
306ci, Pro-m 80 MAF & #42inj, Kirban AFPR, Walbro 255LPH intank & inline, BBK 70mm, Ported Edelbrock #60399, Ported Explorer, Crane 2031 & YT1.72, MSD 6AL, paciemaker tri-y, 2.5" cats into single 3". H/D stall. 3.45 lsd, Powerdyne XB1A.

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 11:11 am 
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dodgie wrote:

Im wondering if with extra boost the stall speed has gone up, and the engines EEC isnt liking it, pulling timing on the transmissions behalf?



This seems most likely at this point. Does it do the same in any gear?
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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 11:46 am 
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Yes same scenario in 1st and 2nd gear.
Cant test it in third on the street, as im not keen on doing 180klms on a public road.
Will test the MSD and check the trans fluid, but I don't think i will find anything wrong.
Still have to pull codes, check TPS ect.

Might have to settle for less boost unless there is a way around this?

 

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ED Fairmont Ghia.
306ci, Pro-m 80 MAF & #42inj, Kirban AFPR, Walbro 255LPH intank & inline, BBK 70mm, Ported Edelbrock #60399, Ported Explorer, Crane 2031 & YT1.72, MSD 6AL, paciemaker tri-y, 2.5" cats into single 3". H/D stall. 3.45 lsd, Powerdyne XB1A.

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 11:51 am 
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I think Jamie(66coupe) from shiftkits.com has a module he makes that tricks the TCU into thinking the stall hasn't been upped. Basically it spits a modified speed/rpm signal into the TCU so it doesn't think the stall speed has increased.
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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 11:58 am 
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Age: 41

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If all else fails I will give that module a go.
This seems to be the unit your talking about...
http://www.shiftkits.com.au/index.php?m ... ucts_id=17
Though I will contact Jamie to see what his thoughts are.
I will also post the results, as I hate threads that dont have a resolution.
Thanks for your time XR9UTE.

 

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ED Fairmont Ghia.
306ci, Pro-m 80 MAF & #42inj, Kirban AFPR, Walbro 255LPH intank & inline, BBK 70mm, Ported Edelbrock #60399, Ported Explorer, Crane 2031 & YT1.72, MSD 6AL, paciemaker tri-y, 2.5" cats into single 3". H/D stall. 3.45 lsd, Powerdyne XB1A.

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 7:14 pm 
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just got your PM - it doesnt seem to be a LHM issue, hi stall LHM will generally hit 3rd gear when launching off the brake at over 2500rpm.

A few questions spring to mind

Whats been done to the ECU / chip etc?
have you tried without the chip if one is fitted?
What is the rev limiter set on the ecu,

Remove any rev limiter chips from the MSD as you only need ONE rev limiter, which is in the ECU. having two rev limiters in series WILL cause problems

nothing else connected to the coil except orange and black from the MSD?

have you verified ignition timing with a light, on a dyno at 5000rpm, then what happens when it falls back to 3600rpm?

TFI module - original wiring or has it been modified? (if you incorrectly put 12v on the start wire permanently, it will cause timing issues above 3600rpm)

Have you tried disconnecting the PIP wire and setting the timing to a reasonable amount (try around 20 degrees for a test) and driving it and see if it is timing related
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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 8:10 pm 
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The ECU has no chip, it has had a J3 chip in it but I took it out to eliminate that possibility.

The rev limit would be the factory limit (6250rpm from memory) but I use a 6000 rpm pil in the MSD. Will pull that out and try it without as part of my trouble shooting.

The MSD is the only thing connected to the coil, using the MSD harness.

I have not verified the timing events on a dyno, as I was hoping to sort this bug out before I spent time and money on the rollers.

The TFI is original without modification.

I have not disconnected the PIP wire and set the timing at 20 deg.
I do put the EEC into self-test mode to set the timing at the factory 30 deg, and have tried 32 deg, but I get nervous when advancing the timing when I can’t hear detonation on a street drive.

I am going to write a list of things to try and eliminate them one by one.
Will post the results…

Thanks for your involvement.

 

_________________

ED Fairmont Ghia.
306ci, Pro-m 80 MAF & #42inj, Kirban AFPR, Walbro 255LPH intank & inline, BBK 70mm, Ported Edelbrock #60399, Ported Explorer, Crane 2031 & YT1.72, MSD 6AL, paciemaker tri-y, 2.5" cats into single 3". H/D stall. 3.45 lsd, Powerdyne XB1A.

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Jan 28, 2011 8:24 pm 
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yeah see how you go with those preliminary tests, also maybe remove the air duct from the blower to the throttle body, pete might also be onto something there, with the throttle blades closing.

If it were a fuel / spark issue it will feel like a miss, or break down when it gets back to 3600rpm, however timing retard will be somewhat smooth with a huge lack of power, and given enough time in this state, your extractors or headers will start glowing red.

Other things to check are fuel pressure and manifold vac / boost (ie no rags or broken / seperating elbows causing an intake restriction?)
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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Sat Jan 29, 2011 7:24 am 
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Try removing the blower belt, then run the same test. It sounds to me like it's boost related valve float. Here's why

60399 uses 110-120 pound valve springs (when new). Centrifugal blowers produce more boost as the revs rise. If you make 13psi boost, this produces just over 40lb's of pressure on the backside of the valve, working against the valve spring. So at this boost level you only have 70-80 pounds of valve spring pressure trying to close the valve which isn't enough. As the revs drop your boost also drops until the valve springs can control the valvesagain, and it runs OK

I run 150lb seat pressure on my supercharged 5.0 engine, and I was concerned this was insufficient. But being a positive displacement blower, the engine doesn't see high rpm to make peak boost so I settled on 150lb.

 

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Sun Jan 30, 2011 11:10 am 
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I don't think I will continue to have valve float after it drops back and maintains 3600rpm until i get my boot out and go again. It's pulled well past 5000prm with 13psi before, though I may have more boost with this different bower.
I am going to lower the boost as part of my elimination process though.

 

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ED Fairmont Ghia.
306ci, Pro-m 80 MAF & #42inj, Kirban AFPR, Walbro 255LPH intank & inline, BBK 70mm, Ported Edelbrock #60399, Ported Explorer, Crane 2031 & YT1.72, MSD 6AL, paciemaker tri-y, 2.5" cats into single 3". H/D stall. 3.45 lsd, Powerdyne XB1A.

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Feb 04, 2011 12:04 pm 
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Not a dead MAF?

 

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Feb 04, 2011 6:01 pm 
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Doubt it, it idles and runs good with a steady decreace in Air/Fuel Numbers, and no other signs of weakness untill it hits 5k. I woldnt think it would be this well behaved if it had a crook MAF.
It is on my list of things to check/clean however.
Im still in the process of elimination, have ruled out a few things but have alot more to go.

 

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ED Fairmont Ghia.
306ci, Pro-m 80 MAF & #42inj, Kirban AFPR, Walbro 255LPH intank & inline, BBK 70mm, Ported Edelbrock #60399, Ported Explorer, Crane 2031 & YT1.72, MSD 6AL, paciemaker tri-y, 2.5" cats into single 3". H/D stall. 3.45 lsd, Powerdyne XB1A.

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 Post subject: Re: Sudden power loss at 5000 rpm. Got me stuffed...
Posted: Fri Feb 04, 2011 11:01 pm 
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Try gaping plugs down to .025 and see if it makes any difference???
You could be blowing the spark out ?? Even with MSD...

 

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