Miss at partial throttle

Torque Monkey

Torque Monkey

The show stopper!!!!!
Joined
Jul 15, 2008
Messages
466
I did a little searching and found a couple people have had the same problem over the years. I didn't really see a resolutio to the problem so I figured I would ask. If this is the way the engine behaves that is fine but I would like to know what is going on with it.

Here is the deal. The engine is a 96 12 valve with some sort of industrial 160 P-pump mounted on it. I have very little history but the price was right so...
Timing is at 16 Deg. The AFC and fuel plate have been modified and last night I installed a set of used 370's I got for a very low price. I currently have an HX40 mounted with a 58mm compressor and the plan is to install an HT3B later once i get it on the road.

I know a lot of people will say that better parts can be found but I am on a shoe string budget and this thing isn't necessarily a daily driver. Bottom line is if it runs crappy at partial throttle I am fine with it....

It is running an A518 auto with no O.D. at the moment (still have been able to source a plug for the trans yet). I took her out for the first trip around the block ever, last night at about 9:00PM. The nieghbors were not impressed....

Anyhow, any insight to help understand this partial throttle miss would be great. If it is the injectors then what exactly is the reason? I am running the thinner copper washer on them to help keep them in the bowl and the timing is extreme by any means.

Here is the picture of the truck so you uunderstand why I am not so concerned about smoke, LOL!
 

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Well, I am guessing by all the crickets that I am on my own with this one. The general consensus is that the delivery valves are causing a flow restriction at partial throttle, this combined with big injectors causes the fuel to enter the cylinder all at once, once it has made it past the delivery valves. My understandi8ng is the duration of the fuel getting injected into the cylinder is changed greatly give the larger injectors.

Anyhow, my solution is going to be installing a 215 pump so I guess none of this really matters.
 
Fuel preesure is 40psi+ (that is where the gauge stops) at all times. I never see it drop...
 
Why don't you throw different injectors at it before swapping pump. Better yet go have your 370s tested and poped for around $150, that is kind of important to have good set of injectors anyway
 
Forrest Nearing said:
when it misses, is it white smoking?
Click to expand...

Maybe a bit of white smoke. Once you get past the point of the miss, maybe 1000 rpm then it clears up and what a ride.

It was the middle of the night so I couldn't see the smoke clearly...
 
Have you checked valve lash?
Assuming lash is ok-

If the problem happens both cold and hot, get the injectors pop tested. You may have a leaking pintle needle that can cause an injector contribution imbalance, especially if the injector quality is questionable.

If the problem is nonexistent or minimal cold, then happens or gets worse when hot, run water on the pump to cool it off while the engine runs and check. If it stops happening, pull dv's and check for metal particles suspended in fuel in the barrels. If metal is present, suspect the pump. Your injectors may be damaged from those metal bits at this point as well, so get them pop tested.
 
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I installed a 215 pump Saturday night to see if it helps amke a difference. I haven't had a chance to start it yet to see if it did. I will when i get home tonight.

Thanks for the advice!
 
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