Missing, dieing. P0300, P0137

[airtight_python]

2002 4.3L Silverado.

Truck started throwing code P0304 (cylinder 4 misfire) long ago. Changed distrubutor cap, rotor, plugs, wires... and the code/misfire persisted. Noticably problematic misfire was intermittent and I never fixed the issue.

Truck then threw code P0137 (O2 Sensor - Bank 1, Rear Sensor). Replaced all 4 oxygen sensors. Code went away for a while (1000-2000 miles?) and has returned. Perhaps the converter is toasted due to misfire on cyl. 4? Converters/y-pipe were replaced once due to some sort of recall, much before the codes ever started.

Truck then burnt the rotor and would not fire, again I changed the cap and rotor. At that time I checked for spark on all cylinders and all cylinders were firing, yet code P0300 persisted.

As of this moment, codes P0300 (random/multiple cylinder misfire) and P0137 persist.

The truck is missing (bad at times and not so bad at times) and sometimes dies. The missing seems to be exacerbated during wet/humid weather... but will sometimes present big problems when the weather is dry. I have always had a problem with the distributor getting water in it when it rains. One of the screw holes for the cap is now broken out and it is held on primarily with high temp silicone and zip ties, but is snug.

I feel I should replace the distrubutor with something other than the OEM unit anyway... What brand is recommended?

I also feel that the missing may have been originally started by the sticking injectors known to this motor. There is a conversion kit available to upgrade them which I may install at the same time I do the distributor.

It is running rich and only getting about 10mpg.

Is there anything else I should look at before I replace the distributor and injectors?

[j cAT]

since this has been used like this for some time now I would say the cat converters are plugged. 10 MPG is about 2X what you should be using my 5.3L 4X4 gets 18-19.5MPG..hywy.



fuel pressure must be 60-65psi key on engine off. if the pressure is lower or rapidly drops to zero after the 2 sec time out you must find out why ..injectors / fuel reg. / fuel pump. perhaps a little of all....

2002 has fuel filter and should be replaced every 40,ooomi on average but that depends on how the fuel is handled by the supplier.

off brand fuel usually causes fuel system damage.

the fuel system on these vehicles is good with the proper maintence and keeping the fuel level above 1/4 tank.

[j cAT]

water in the distributor is from the ac evap system piping I believe. this must be insulated with foam covering etc.

arcing in the distributor My guess is the ICM has been damaged. this can be tested at autozone if they have the WELLS MODULE tester.

cap/rotor should be replaced if any arcing / carbon tracking .

[airtight_python]

I appreciate the input j cAT

I had heard about the AC lines dripping onto the distrubutor as well. They're all insulated up well and shouldn't be the issue. Even under the hood still looks nearly like new in this truck.

The cap/rotor were replaced ~500 miles ago. The problems existed before the rotor burned up, and still exist.

I agree that the bank 1 converter is probably plugged... bummer. $400-$600 part.

I'm going to use my new fuel pressure gauge this weekend and see what it's doing. My guess is sticking injectors along with plugged converter.

[j cAT]

with water getting to the distributor this is the only way is from the ac system piping..

if this were a 1972 v8 buick the distributor is directly behind the engine fan . wet weather with a poor fitting cap this was big trouble.

I would redo the insulation on these ac pipes.

[airtight_python]

The water in the distributor is happening in humid or wet weather. It has been an issue since new. Pretty hard for the A/C lines to collect condensation when it hasn't been turned on in months.

I don't believe the missing to be completely caused by condensation in the distrubutor, however the missing sure gets a lot worse during wet weather.

[j cAT]

Originally Posted by airtight_python

The water in the distributor is happening in humid or wet weather. It has been an issue since new. Pretty hard for the A/C lines to collect condensation when it hasn't been turned on in months.

I don't believe the missing to be completely caused by condensation in the distrubutor, however the missing sure gets a lot worse during wet weather.

If this were my problem the plug wires will be removed and inspected for cracks or cuts. the boot ends will have silicone dielectric grease placed in side the boot. the wires will also be measured for proper ohms. any wires with high resistance over the average are defective . this can cause arcing .

the rotor will be removed and any carbon in / on the cap rotor these will be replaced.

on the ac system and the condenstion. even though you may not command the ac cooling to come on the compressor will work and produce condenstation in other modes of operation. the condensation issue is an old one as this was from day one a problem that in most all cases was corrected years ago but things happen where this is undone.

missfires as I mentioned before are the norm with plugged converters or restricted exhaust as well as other components like fuel supply issues .

with some testing/inpecting you should have a good idea how to correct this.

new does not mean GOOD !

[airtight_python]

Appreciate it...

[phipps]

I have a 97 with the 4.3 and was having missing issues. I replaced cap, rotor, wires, plugs, coil and the problem persisted. Turned out to be a worn distributor gear. Apparently lots of issues with worn gears. I replaced the complete distributor and the miss went away.

[j cAT]

Originally Posted by airtight_python

Appreciate it...

If you find the time post back what you found.

once I had a bad fitting distributor cap water/mositure got in . the arcing created hydogen , cap blew off. that was in the 60's