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Discussion Starter · #1 ·
Hi Gordon,

302 shortblock, EFI, no emmissions except PCV, X3Z, 24# injectors, GT40 intake, Trick Flow Twisted Wedge heads, 70mm Mass air sensor (F1SF-12B579-AA HFH70-02 1E15), 65mm TB, E303 cam. Last week I changed distributor, coil, and plugs (Autolite 3924, 034 gap). After ~ 60 mile drive, plugs appear almost new, lean.

Since I built my Mark II in 2004-2005, the car runs great except at low rpms (<2000) it bucks and jerks. Yesterday, after years of puttering, took it to a local (Prescott, AZ) mechanic/racer known for work on 302 EFI's.

After a day of tweaking and driving the car he's convinced I need more fuel: 32 or 36# injectors and a matching Mass air sensor.

Is this a step in the right direction to cure the buck/jerk problem?
 

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Pro FFR Builder and Moderator
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What ignition system are you using?
 

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Official OLD GUY
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Ignition

Your signature says MSD, has it given you this issue before or is this new since the dizzy change?

Your setup is almost like mine, short of the TW heads, and larger injectors/mass-air meter. I run a stock 302 with an E303 cam, 4-into-4's and the GT-40 upper and lower and don't need 24# injectors or a 70mm mass air meter, why do you feel you need this much air intake? Going to 32 to 36# injectors will only compound the proplem . . . are you running a blower or turbo's, or am I missing something here?

I'm going along with Gordon here, sounds like an ignition issue.
Also, new plugs running on unleaded fuel and only 60 miles should look lean (almost new), in my opinion. 60 miles of racing or 60 miles of freeway cruising?

How much fuel pressure are you getting . . .

Almost sounds like a vacuum leak to me . . . Just my 2¢

We need more info

Doc
 

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Discussion Starter · #4 ·
Currently (for last 60 miles): MSD 6AL, Summit Disty SUM-850411, MSD Street Fire Blaster TFI Coil PN 5527

Since 2005 until 60 miles ago: Same MSD 6AL, MSD Disty Pro-Billet PN 8456 (kept having lots of build-up on all 8 posts inside), MSD Blaster II coil.
 

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I also would like to know just how much fuel pressure you are making. You have plenty of injector to make 400hp and you are nowhere near that.
Things to look at TPS voltage and idle screw adjustment- They are related, one effects the other.
Fuel pressure- what it's at and is it drops or increases when the throttle is wrapped.
Fuel pump size? Adjustable regulator?

One of the thinks I have seen is if the throttle plate screw it turned to far in holding the T-plate open to mush you will get a lot of surging and bucking at low revs.
 

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Discussion Starter · #6 ·
Yes, new plugs look new, makes sense. Old ones on bench look the way they are supposed to.

Same issue (bucking) before/after disty change. Fuel pressure set @ 39# w/vac plugged, runs at~ 33 with vac. at idle.


The 60 miles was a circuit intended to reflect all driving conditions; starts/stops, highway cruising, suburbs, and WOT.

No blower.

The reason I'm in this position is that I'm not a gear-head and just picked blingy stuff from Summit during the build without realizing the impact of component interaction. Learning now that that was a big mistake and am looking for a way make the car that I love driving more enjoyable.

Thanks
 

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Make a day trip and come down and see me.
 

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Discussion Starter · #8 ·
Adjustable FP regulator. When reved, FP increases, then backs-off; 155l pump. TPS @ .964. I'll mess around with the TB screw.

Great idea about the day visit! I'll be coming to the valley quite abit over the next month or so; I could leave it with you for a week?
 

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Discussion Starter · #10 ·
Terrific! I'll call before coming down. Thanks!
 
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