little help needed
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Senior User
Joined: Jul 2007
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From: south jersey
little help needed
hey guys.. i finally got thw swap done on my 94 f150... originally had a 302 but i had a 351 windsor put in....just picked it up from the exhaust shop and drove it around and it seems to crusie around ok but when i give it full throttle it seems to break up.. not sure if its a fuel issue or not cause it still is the 302 wiring harness... any help would be great
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What's the firing order of the 302, compared to the 351? I know for sure the 351 has the same firing order as the 302s in Mustang and Mark VIIs, but the truck 302 I think uses the same firing order as the fullsize cars and that one is different from the HO/351 firing order. The issue with all this is not just the spark plugs order on the dizzy cap, but with the injectors as well - the '94 302 is a SEFI system, meaning each injector fires just before the intake valve opens, as oposed to the batch-fire system where the injectors fire in groups of 4 at a time. I think the 351 always used batch-fire and never got a SEFI setup...
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Joined: Apr 2008
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Is there a 351 ECM with mass air and SEFI? Cause if there ain't and the 351 ECM uses the batch-fire, you will end up with just two injectors firing, unless you swap in a batch-fire engine harness as well. I apologize if this is all a moot point, I do not know enough about the truck Windsor engines, but one of my friends has an '86 F150 with a 351 that he converted to SEFI using a mass-air SEFI harness and a matching 302 ECM (believe tis the A9L), then he Tweecer-ed it to work with the larger airflows associated with the 351 displacement.
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Lead Driver
Joined: Nov 2002
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From: Concord, NC
You are right about the 351 being batch injected, but since nintey4f150 is using the 302 SEFI computer and wiring, he won't experience that problem. If he were to install a batch injected 351 computer into the 302 wiring, then yes, it would be running on two cylinders.
Is there any way you can monitor fuel pressure while driving? If fuel pressure drops when the engine stumbles, you may have a weak pump. One thing you might try is to clean the MAF sensor heating elements. If they are dirty, the computer will interpret less mass air flow and will inject less fuel, leaving any adjustment up to O2 sensor feedback. The range of adjustment based on O2 sensor feedback may not be enough to prevent the stumble at higher loads and rpms.
Is there any way you can monitor fuel pressure while driving? If fuel pressure drops when the engine stumbles, you may have a weak pump. One thing you might try is to clean the MAF sensor heating elements. If they are dirty, the computer will interpret less mass air flow and will inject less fuel, leaving any adjustment up to O2 sensor feedback. The range of adjustment based on O2 sensor feedback may not be enough to prevent the stumble at higher loads and rpms.
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Thread Starter
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Senior User
Joined: Jul 2007
Posts: 248
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From: south jersey
well i just drove to dairy queen and it was good for a little bit just crusing but then it started missing and running like crap... but i later drove it and it was ok and then the ssame thing happened
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Joined: Apr 2008
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You are right about the 351 being batch injected, but since nintey4f150 is using the 302 SEFI computer and wiring, he won't experience that problem. If he were to install a batch injected 351 computer into the 302 wiring, then yes, it would be running on two cylinders.
Is there any way you can monitor fuel pressure while driving? If fuel pressure drops when the engine stumbles, you may have a weak pump. One thing you might try is to clean the MAF sensor heating elements. If they are dirty, the computer will interpret less mass air flow and will inject less fuel, leaving any adjustment up to O2 sensor feedback. The range of adjustment based on O2 sensor feedback may not be enough to prevent the stumble at higher loads and rpms.
Lead Driver
Joined: Nov 2002
Posts: 9,557
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From: Concord, NC
Oh, okay, I misread you then - I thought you suggested running a 351 computer, hence why I pointed out the whole batch-fire vs SEFI thing.
So now the MAF is reading higher flow numbers at any given engine speed (just cause tis a 351 engine, and not a 302), what if those flow numbers are out of the ECM's acceptable range? Again, I don't know how wide that acceptable readings band os fir this 302 ECM, but wouldn't that make sense?