Another case of Bucking

Callmewhitexr7

Registered User
I just got the motor out of my wrecked 89 XR7 out and put into an 89 SC that I bought. Well the motor never Idled this good when in the cougar, dont know how it runs cause of a new clutch, well anyways when It goes under boost its starts to buck. The motor never did this in the cougar, could it just be a clogged fuel filter?? Thanks


NICK
 
99% of the time bucking under a load is caused by a bad plug wire. It's likely one or more of the wires were damaged during the engine swap.

David
 
Thanks I was thinking that too cause I did have to pull the plugs off they are under warranty so i will get some new ones thanks alot.

NICK
 
I meant wires. But anyways I changed out the wires and it still does it but not as bad. I checked the fuel pressure with a tire gauge and it says 25 thats with the car running. Are tire gauges even very acurate? Thanks for all the help.

NICK
 
Nick,

It could also be the fuel filter like you mentioned in the first post, but usually it boggs more than it bucks when the filter is clogged.
No you can't use a tire pressure gauge to check the fuel pressure, you need a fuel pressure test gauge, they sell them at autozone for about $35.

I don't really think that's the problem but if you do get a gauge, the pressure should be about 40 psi with the vacuum hose removed from the pressure regulator and around 35 psi with the hose attached. Pressure will vary with the hose attached so it's best to check it with the hose off. With hose attached if you goose the throttle quickly and see 10 pounds of boost you should also get 50 pounds of fuel pressure. Fuel pressure should increase pound for pound with boost.

Make sure the wires are seated good onto the plugs. Did you change the plugs while you were doing the wires ? If the plugs were in the engine when you made the swap, one of the insulators may have got cracked by bumping into something.

David
 
Thanks I'll check that, this motor had nowere to hook a chain to pull it so i just ran it threw the exhaust manifold, maybe when i did that it could have messed up the plug I'll change them out what should I get and what should i set the gap for. I have no mods. thanks


NICK
 
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