Let's see who's got a big brain!!

[sporty1]

I have a 1986 SVO Mustang with a problem. Upon deceleration the engine bucks somewhat violently. Its worse coming sharply off of boost but seems to be present under no boost condition(as read on the factory pressure guage)as well. When the engine bucks, you can hear a flutter that sounds like the VAM trap door, but I can't be sure. I checked for obvious vaccum leaks, and have replaced the WG actuator. It feels like a blow-off or bypas valve would help this but I don't think its the solution to the problem. Any insight into this problem would be much appreciated.

[kiwi]

?

How much boost before decell?

[SVOeric]

It feels like a blow-off or bypas valve would help this but I don't think its the solution to the problem

YEP!!

I think this thought is right on the money...

[kiwi]

I was......

...leading to that Eric......He might try & reverse the BPV~If he is bleeding off boost runnin' 20 plus......

[SVOeric]

I'm reading that he has no BPV at all -- but I could be wrong.

Without a BPV or BOV -- on my car, I have had it jerk at 10 psi boost when jumping in, and out of the throttle quickly

EDIT :: Oh yea-- to help until you do get a bpv, or bov -- when you decelerate, take your foot off the pedal slowly, don't just pull your foot straight up -- see if this helps.

[svobud]

Re: Let's see who's got a big brain!!

Originally posted by sporty1
When the engine bucks, you can hear a flutter that sounds like the VAM trap door, but I can't be sure.

My understanding of this noise - is - it's the impeller wheel screeching to a stop. Mine made the same noise .. UNTIL I put a BPV inline.

[NY eric]

Dito

Once I uped my IC my turbo made the same flaper closing noise too when I shifted under heavy boost. I installed a BPV and then that noise stoped and I heard a honking (BPV was backwards) now all good.

[kennycoulter]

wasnt there a bpv buy that yous guys did recently from tiny avenger? for $100 roughly? is there any advantages of a bpv over a bov or vice versa? sorry to "highjack" i already tried the search, but didnt find anything about a sale.

[Will]

BPV's are suppose to be better for vane air metered engines than BOV's that vent bypassed air to the atmoshpere. There are a few like Forge and Bailey BOV's that 2.3 turbo guys have used with sucess since they are of the dual piston design. I use to run a JDM adjustable BOV on my SVO I got off of eBay for $30. I used a hole saw to cut a hole in the intercooler and welded in a 1" diameter aluminum tube and mounted the BOV with a rubber hose. Worked OK and I didn't sense any rich running conditions. Also made that cool pssst sound between shifts the ricer crowd loves so much.

[turbizzy]

My car did this as well a while back and my TPS had a flat spot near off idle and whenever the pedal would get near it accel or decel, it would do that. Doesn't hurt to check your TPS for smooth sweeps.

[sporty1]

Engine Shuddering

Thanks for all the response. To begin with the vehicle has neither BOV or Bypass valve. And I'm still working the bugs out of of a Joe P MBC. (the pressure off of the compressor housing port is insufficient to control the WG actuator, I'll T off of the intake on Thurs and see) But, this was a problem when the factory boost controller was installed. This problem is present under none to minimal boost as well as 18 PSI (since my MBC isn't working, I have infinite boost with a lead foot, I keep it under control for now).

I saw both the Forge Bypass and Blow off valves and I like the design, however for simplicity, and effectiveness I would rather weld a threaded bung onto the Intercooler and screw on a BOV there. However, this fix dosen't address the problem. I don't think that the factory would have convinced buyers of the need for a bypass valve to make a 2.3 turbo motor to function properly.

I have a code scanner that should work on this EEC-4 system, I'll look for codes and perhaps a dead spot on the TPS.