Still Have the P0304- 6 months and more $$$

gbsharon

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As per previous posts, am still chasing a cylinder 4 misfire. This happens when I am pulling up long hills and is way worse under load i.e. with passengers or a trailer. I wanted to go into a bit more detail and see if anyone could help. Started noticing going uphill- would get a random misfire code. Took the car to mechanic and was told dirty injectors- car was seafoamed (or equivalent) on machine. Ran well for about 2 months after this (towed and drove up hills no worries). After another 2 months, mis came back. Took to another mechanic who told me it was the injector spider. Had the updated MPFI spider put in along with new upper intake gasket at the same time. Although this got rid of the random misfire, I was now dealing with a P0304. I can feel when the miss is getting bad- front of car starts to vibrate with increasing force. Does not trigger a code until I push it further. Backing off the throttle usually calms her down a bit and the vibration eventually goes away. Took to original mechanic who said they would figure it out- performed leakdown test and compression test, both with positive results. I have since replaced the following myself all with AC Delco or OEM equivalent parts:

Plugs
Wires
Distributor Cap
Coil
Fuel Filter
Crank Position Sensor
T-stat (unrelated but done nonetheless)

Also New:
MPFI Injector Conversion
Upper Intake Gaskets
Fuel Pressure Regulator

What steps can I take to check from here? I really am tired of guess work.

From research, I have narrowed it down to the following:
- Bad ECU
- Bad valve springs
- Bad valve

I was told the fuel pump was good by a mechanic, but I really wanna double check this. Is it possible that it is supplying adequate pressure but not adequate flow?

Car runs really well on flat ground and starts right up every single time.

Thanks,
gb
 

parkerpress

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@gbsharon: Just following up again. I'm still having issues and really like the truck. I'm starting to think my nextstep will be replacing the engine completely.

Over the years, I've done the following, a lot of which are trying to solve this problem:
* Oxygen Sensor
* Fuel Pump/Pressure Regulator
* Idler Arm / Alignment
* Mass Airflow Sensor
* Distributor-Rotors
 

Fless

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Might want to start your own thread. The OP hasn't been on here in 5-1/2 years.
 

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