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Bucking under boost...

B

boondoggie

New member
Joined
Nov 12, 2002
Location
New Hampshire
Rut roh! :shock:

So, my 780T starting stumbling/bucking whenever under load and above about ~8psi...

I'm thinkin it's fuel, no? Thoughts?

1990 B230FT, TD04H-13C, 3"exh, boost at 12psi, new cap/rotors/wiresplugs about a month ago...
 
My money would be on fuel delivery. Filter, pre-pump, main pump or somewhere in the pressure regulating. Change the filter, if it's not that it's probably the pre-pump. Then check the main pump, and fuel pressures.
 
My B230FT is doing the same thing except i am only running 5PSI cuz of wastegate problems, but under heavy boost it tends to buck. mines a 89 780 B230FT, i swapped it in after my 740 B230FT went out.
Let me know if it stops after you change your fuel filter
 
i'd agree with the cbv assesment. my '89 780T did the exact same thing. it turned out the the cbv had become unbolted and was leaking air. i was blowing some serious black smoke too.
 
It can be ignition related-check your plugs, wires, cap, and rotor. Not kidding, it sounds more like an ignition related issue imo but without the car here its hard to say.

BR
 
Well a little more info...

It started doing it about 3/4 of the way thru my 30 minute commute yesterday morning. On the way home, same thing; starts off fine, toward the end it acts up. This morning all is fine...

This weekend I'm gonna change the dist cap (the one I had put on had a little tiny crack from kicking around my garage too long, but I put it on anyhoo cuz I'm a cheap bastard) the FI relay (just cuz it's $14) and the fuel filter, cuz I have one sitting on the shelf.

I'll let ya'll know how it goes... :x:
 
boondoggie said:
Well a little more info...

It started doing it about 3/4 of the way thru my 30 minute commute yesterday morning. On the way home, same thing; starts off fine, toward the end it acts up. This morning all is fine...
Click to expand...

I'm putting my money on some sort of exhaust restriction, but that's a long shot.

Good luck.
 
[quote:fe49075c61]I'm putting my money on some sort of exhaust restriction, but that's a long shot. [/quote:fe49075c61]

Nah... that's the pumps. After driving for a while they heat up and the electrical resistance increases, then they get weak.

-steve
 
I still say its ignition related though, could be a misfire at higher revs. I had a similar issue and swapped plugs,wires,cap,and rotor and problem was fixed. 8)

Late.
 
Slow745ti said:
I still say its ignition related though, could be a misfire at higher revs. I had a similar issue and swapped plugs,wires,cap,and rotor and problem was fixed. 8)
Click to expand...


I agree. I could be. It is harder to strike a spark under load. If you have old leaky HT wiring, rotor, distributor- replace them. Do yo have a Bosch platinum plugs? Some may disagree but these things are crap in a long run and even Bosch will tell you not to use them in turbos. I had one where the center electrode fell out and two where the internal resistor burned out. These two were still firing as the high voltage was still punching through the resistor but now you had the spark jumping three gaps instead of two. I use NGK platinum now. So far so good. (one year)
 
I wouldn't use Platinums in any sort of a performance vehicle. NGK all the way!
 
I had this problem and it seemed to be related to the "turbo-plus" circuit that dumps vacuum to the waste gate under full pedal.
Look for a vacuum line on a tee off the turbo going to a module directly behind the rignt headlight. Clamping this line off removed the bucking.
Replacing these vacuum lines fixed my problem...
Local shop clued me to this... didn't know the 780 had "turbo-plus".
http://myhome.starstream.net/jayf/89_780_turbosys_diagram.pdf
 
boondoggie said:
Rut roh! :shock:

So, my 780T starting stumbling/bucking whenever under load and above about ~8psi...

I'm thinkin it's fuel, no? Thoughts?

1990 B230FT, TD04H-13C, 3"exh, boost at 12psi, new cap/rotors/wiresplugs about a month ago...
Click to expand...

Fuel starvation, 2 780s had the same problem he changed out the Volvo pumps for an intank Welbro 255 lph high pressure. He is happy as a pig in ___ now!
 
Wow... posts from the past... :)

My problems were just that I was a cheap SOB and thought I could get away with running a cracked dist gasket... why it only happened under boost is anyone's guess...

:volvo:
 
Anonymous said:
Wow... posts from the past... :)

My problems were just that I was a cheap SOB and thought I could get away with running a cracked dist gasket... why it only happened under boost is anyone's guess...

:volvo:
Click to expand...

duh huh... loggin in helps... :-P
 
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