After about 30-40 miles. my 96 will through the p0300 with no ill effects felt in running condition, other than a possible slight drop in power.

new cap
rotor
plugs
wires and
distributor

freeze frame data:
Load: 9.8%
ECT: 194*
FTB1ST:3.125%
FTB1LT:3.125%
FTB2ST:3.125%
FTB2LT:6.25%
Manifold Pres: 6.527psi
RPM: 1693
Speed: 52.195mph
MAF: 19.65g/s

any help is appreciated as to isolate the cause

 

1. These engines are very fussy when it comes to tune up parts. What brand of parts did you install?

2. Did you check & adjust camshaft retard after replacing the distributor?

3. Have you checked fuel pressure and leakdown? If so, what were the readings?

 

Napa tune up parts.

cam retard is -2*

and have not checked fp, ill check asap

 

Might want to ditch the NAPA cap & rotor and install an AC Delco, it does make a difference. All fuel trims indicate a slightly lean condition, so there might be a fuel delivery issue. Could be partially restricted, (dirty) injectors, slightly low fuel pressure or excessive leakdown. Key on, engine off, fuel pump running: Pressure must be 60psi to 66psi, and it must remain above 55psi for at least 10 minutes after the pump shuts off.

 

thread revival


all sensors read correctly. if I floor it and drive like a madman I set lean codes on both banks. fuel pressure is 48-53ish psi, running, koeo, and revved up. does not leak down


that sounds low to me, but many well established and personally trusted mechanics say its not that low, opinons?

 

Post #4 has the GM factory specs when testing at the service port near the distributor. If one or both of those tests fail, fuel pressure and leakdown must be tested at the fuel filter outlet, (to determine where the problem is). All fuel pressure and flow must end at the fuel pressure tester, (no fuel is allowed to the engine). Pressure must be 73psi to 108psi while the pump is running. It must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of the test, the pump is at fault. If if passes both tests, the problem is in the plenum. GM does not publish any "engine running" fuel pressure specs for this system. All fuel pressure and leakdown tests are made with the engine off. If fuel pressure is low, and or leakdown is excessive, there will be driveability issues, including DTC's for lean fuel mixture.

 

New Fuel Pump, new fuel filter, it still stumbles slightly, but has far greater throttle response and power. i still feel as though something is wrong. the injectors passed the resistance test. and i have pulled the plenum to clean them, i left the hub alone and clean the nozzles. what are the chances of contamination on the injector screens?

another development is that the truck likes to run on premium, but its favorite fuel is Rec fuel(90 oct 0% ethanol). after the pump it seemed to take 87 like normal.

thoughts?

 

Injectors are not likely to be the problem.

These engines are tuned for 87 octane. Using higher octane fuel can cause it to run worse due to the lower flash point and faster burn rate.

Is the check engine light on? If so, what DTC's are in memory? Have you checked fuel pressure and leakdown? If so, what were the readings?

 

i runs better on premium, the fuel pump is new, even the old pump did not have leakdown. i replaced the pump because of the low presure readings.

only dtc's are the intermitten p0300 and if you run around at full or heavy throttle it will throw lean codes

 

Is the check engine light on? If so, what DTC's are in memory? Have you checked fuel pressure and leakdown since replacing the fuel pump? If so, what were the readings? If not, check them and post the readings.