North American Turbocoupe Organization



Low boost stutter
Cerebral Offline
Senior Member
#1
I have had a problem for a long time with the car bucking at low boost part throttle, such as passing someone while in 4th or 5th gear. Exactly like this post that no one ever solved:

http://forum.turboford.org/cgi-bin/ultim...010#000005

I got used to just putting the pedal down further so I wouldn't have that problem. Now, I have to drive on the highway at about 75mph for 20 minutes every day to go to my new job. At 75 it does the same thing as when I try to pass at part throttle. It bucks and sputters, I tried to just put the pedal down some more after it started and it just backfired and bucked harder so I have to let completely off and reapply the throttle. If I slow down to 70, I won't have the problem.

It has new plugs, wires, coil, BP Sensor, TPS, complete distributor. I'm at a complete loss.
1987 Automatic TC- parts car

1987 5 Speed TC, K&N on Vam,Boost controller, T3, Bob's Log, Stinger 3 inch exhaust with Magnaflow, FMIC, Forge Dual Piston B.O.V., Ranger Roller, Esslinger Adjustable Pulley, Boport Drop in Valve Springs, Pyro Pete Clutch
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Pete D Offline
Administrator
#2
Backfire can often be a sign of a timing problem. I'd start with checking the cam timing and then the ignition timing.
I'd also look for a air leak ahead of the throttle body.
Pete Dunham


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Cerebral Offline
Senior Member
#3
I triple checked all of the hose connections, the cam timing is good and I have ignition timing at 12*. I just checked the vam and my VREF is 5.98V and when I open the door inside, the signal goes from .28V to 5.5V. The write up I used to test it said that the signal should be 4.5 Max. I tested 2 different Vams and they both had the same reading.
1987 Automatic TC- parts car

1987 5 Speed TC, K&N on Vam,Boost controller, T3, Bob's Log, Stinger 3 inch exhaust with Magnaflow, FMIC, Forge Dual Piston B.O.V., Ranger Roller, Esslinger Adjustable Pulley, Boport Drop in Valve Springs, Pyro Pete Clutch
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powerstrokin Offline
Junior Member
#4
Mine was doing this for awhile just prior to the timing belt going out. A couple bad/missing timing belt teeth were causing the issue, then the belt lost a bunch of teeth.
'88 Turbo Coupe
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Cerebral Offline
Senior Member
#5
It has a new timing belt and it did it before the belt change.
1987 Automatic TC- parts car

1987 5 Speed TC, K&N on Vam,Boost controller, T3, Bob's Log, Stinger 3 inch exhaust with Magnaflow, FMIC, Forge Dual Piston B.O.V., Ranger Roller, Esslinger Adjustable Pulley, Boport Drop in Valve Springs, Pyro Pete Clutch
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Pete D Offline
Administrator
#6
What about hose leaks. VAM hose can wear on the bottom side (out of sight) and I've seen IC hoses split and crack (BTDT)
Pete Dunham


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Cerebral Offline
Senior Member
#7
Vam hose checks out I took all the silicone couplers loose and inspected them and they check out too. Any other ideas?
1987 Automatic TC- parts car

1987 5 Speed TC, K&N on Vam,Boost controller, T3, Bob's Log, Stinger 3 inch exhaust with Magnaflow, FMIC, Forge Dual Piston B.O.V., Ranger Roller, Esslinger Adjustable Pulley, Boport Drop in Valve Springs, Pyro Pete Clutch
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George Offline
Member
#8
What Pete said. Sounds like cam timing maybe a tooth off. Although, mine was a tooth off when I changed the timing belt over the weekend and it ran like crap. Sounded weird when it idled. Kinda freaked me out so I redid the cam timing. Purred like a kitten.

If you can get ahold of a scanner, check for codes. Might be a problem that only shows up under certain engine parameters.

On a side note, my car did pretty much the same as yours on a couple of occasions but that was before I put the new timing belt on. Only driven it once to work. Once my clutch is broke-in I'm gonna romp in it to see how it runs under boost.

Good luck.
88 TC with reman Airesearch T3 .58ar, Walbro 255, cone filter, Gillis mbc set @ 17psi, Mustang A-pillar pod with vac/boost and a/f, full 3" single exhaust w/ Dynomax ultraflow muffler and header, recirculating BOV custom tapped to factory intercooler
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natmac3 Offline
Administrator
#9
if you run and egr, try disconnecting it and/or blocking it off & see if trouble persists.

if you have the BOV vented to atmosphere, try increasing the spring preload.

if these dont change the behavior, i'd wonder if maybe a slight increase in fuel pressure might help. isnt it possible that the bigger turbo, engine rpm, and cam timing hit a "sweet spot" where the afr is outta wack... do you have a wideband o2 or can you log afr's at all?
1987tc
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1988turbotbird Offline
Senior Member
#10
Did you check fuel pressure?
88 TC/HX35/CAI/3" exhaust/Wilson MS2/Beanman header/Head Work/Laramee Cam/Gillis boost controller/3G alt/Walboro 255 fuel pump/BOV/CHE rear control arms/1" lowered/poly. bushings/Chuck W mounts/6 puck clutch/Pro 5.0 shifter/AEM wideband/Tuning MS..
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