High Speed Stutter
Thread Starter
Intermediate
Joined: Jul 2009
Posts: 44
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From: North Dakota
High Speed Stutter
I have an 86 951 that has a stutter or stumble when I mash the gas at high speeds. It is like it is dying out. Hard to describe. It happens at different boost levels but typically at higher rpms. It also seems to not happen as often if I ease into the gas instead of flooring it. It usually shows itself out on the highway while passing. I have changed the afm to see and no change. The car has a boost enhancer and k&n filter and is pretty much stock otherwise. It seems like a fuel issue but Im not sure where to start. Any suggestions or people that have had a similar problem?
Burning Brakes
Joined: Apr 2008
Posts: 1,244
Likes: 1
From: in my 944,NJ
Check the wires and the distributer cap to make sure its nice and secure and tight. I had the same problem but with start up from a red light. It just stuttered slowly then accelerated normally after a while. I popped the hood and the distributor cap was just lose, hanging on one hook screw vs both screws.
Advanced
Joined: Sep 2009
Posts: 76
Likes: 0
From: Lakeland, Florida
I had the same problem with my '86. It turned-out to be a broken hose from the banjo bolt (located on the pressure tube to intercooler) to the cycle valve that controls the waste gate opening. My break was between the banjo bolt and the hard line. Since you have a boost enhancer in place there, and assuming that that hose is in good shape, you could have a break at the other end near the cycle valve.
What happens when the hose is broken is; your cycle valve gets no boost signal. Since it thinks that you're not producing boost, the waste gate remains closed. The car might actually feel a bit quicker as it is holding boost. On high boost though, such as when you floor it in a higher gear to pass, the over-boost protection kicks-in since your waste gate isn't opening to release it, and it feels like your engine is cutting out.
I'm not sure if this is your issue, but several inches of new hose solved it for me. That was before I got my boost enhancer. Good luck.
What happens when the hose is broken is; your cycle valve gets no boost signal. Since it thinks that you're not producing boost, the waste gate remains closed. The car might actually feel a bit quicker as it is holding boost. On high boost though, such as when you floor it in a higher gear to pass, the over-boost protection kicks-in since your waste gate isn't opening to release it, and it feels like your engine is cutting out.
I'm not sure if this is your issue, but several inches of new hose solved it for me. That was before I got my boost enhancer. Good luck.
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Thread Starter
Intermediate
Joined: Jul 2009
Posts: 44
Likes: 0
From: North Dakota
I have NGK bpr 6es plugs in it gapped to 27-28. Could that be the detonation problem? I am ordering some of the magnacore wires either way. Also when I was checking the hose off the banjo to the boost enhancer I noticed that the boost enhancer was swiveling. Turns out the locknut was loose on the BE. I tighted it down but should I put some type of thread sealant in there? Also, the LBE isn't enough to warrant putting in NGK bpr7es is it? Thanks for all the help so far.
Advanced
Joined: Sep 2009
Posts: 76
Likes: 0
From: Lakeland, Florida
[QUOTE=nddoublea77 Also when I was checking the hose off the banjo to the boost enhancer I noticed that the boost enhancer was swiveling. Turns out the locknut was loose on the BE. I tighted it down but should I put some type of thread sealant in there? Also, the LBE isn't enough to warrant putting in NGK bpr7es is it? Thanks for all the help so far.[/QUOTE]
I'd diagnose one thing at a time. With the loosened boost enhancer, is it possible that the setting was changed, either by accident or purposely at some time? Normal BE setting is around 10 psi. Too high a setting might produce the symptoms you described. To rule out the BE, you might try just replacing it with a well-clamped hose as in the stock configuration. Take it for a ride. If the problem's fixed, the BE was the culprit. If not, then put the BE back and check into the other stuff.
I'd diagnose one thing at a time. With the loosened boost enhancer, is it possible that the setting was changed, either by accident or purposely at some time? Normal BE setting is around 10 psi. Too high a setting might produce the symptoms you described. To rule out the BE, you might try just replacing it with a well-clamped hose as in the stock configuration. Take it for a ride. If the problem's fixed, the BE was the culprit. If not, then put the BE back and check into the other stuff.
Thread Starter
Intermediate
Joined: Jul 2009
Posts: 44
Likes: 0
From: North Dakota
Will do. My wires wont be here until next week anyway. Is that BE adjustable by turning in or out that nut? I assume it is putting more or less tension on a spring inside. The highest I have seen my boost go on my autometer gauge is 14. I will pull it and check.
