'97 5.0 Vortec P0302 (& Occasional P0300)

TBuzz · September 30, 2007

New to forum and have checked same for similar problem but none close enough to be helpful.

New Plugs, Wires, Cap, Rotor (All AC Delco), Injectors (GM) & Ign. P/U Coil (Borg Warner). Changing wires and plugs does not change P0302 code (to other cylinder).

Have not had distributor out, but have loosened hold-down bolt and moved distributor both directions and tried many positions inbetween. This seems to alter the appearance time to P0302 code (and occasional P0300), but P0302 consistently returns, setting MIL (and flashing) within ~10 minutes driving time.

I'm concerned now that I've moved distributor that I'm unable to get advance/retard close enough to eliminate that as problem. V

Vehicle runs well, although I can feel very slight misfire at idle.

Advice in getting distributor properly repositioned, along with any assistance in addressing continuous misfire and P0302 code would be most appreciated.

Terrific forum.

blue-ss-camaro · September 30, 2007

New to forum and have checked same for similar problem but none close enough to be helpful.
New Plugs, Wires, Cap, Rotor (All AC Delco), Injectors (GM) & Ign. P/U Coil (Borg Warner). Changing wires and plugs does not change P0302 code (to other cylinder).

Have not had distributor out, but have loosened hold-down bolt and moved distributor both directions and tried many positions inbetween. This seems to alter the appearance time to P0302 code (and occasional P0300), but P0302 consistently returns, setting MIL (and flashing) within ~10 minutes driving time.

I'm concerned now that I've moved distributor that I'm unable to get advance/retard close enough to eliminate that as problem. V

Vehicle runs well, although I can feel very slight misfire at idle.

Advice in getting distributor properly repositioned, along with any assistance in addressing continuous misfire and P0302 code would be most appreciated.

Terrific forum.

I have the same problem except mine is a 5.7 and it is a p0304 code. I was told injectors and have not tried that yet but i see you already replaced the injectors next I was also told the distributor goes bad in these truck. I have not solved mine yet. If you solve yours please let this board know so I can try the same thing. good luck.

atboley · September 30, 2007

well it seems to me that unless you screwed somthin up when you replaced it, that you gotta have a compression problem, have you checked compression? and if you moved your timing, your screwed, the only way to set it is with a tech 2 scan tool, or maybe ther is aftermarket ones that do it, but i dont know... you neeed to check comression, then if that is ok then you need to take it somwhere that has the right tools to set the timing... then check if you have injector pulse on cyl #2????

atboley · September 30, 2007

well it seems to me that unless you screwed somthin up when you replaced it, that you gotta have a compression problem, have you checked compression? and if you moved your timing, your screwed, the only way to set it is with a tech 2 scan tool, or maybe ther is aftermarket ones that do it, but i dont know... you neeed to check comression, then if that is ok then you need to take it somwhere that has the right tools to set the timing... then check if you have injector pulse on cyl #2????

atboley · September 30, 2007

well it seems to me that unless you screwed somthin up when you replaced it, that you gotta have a compression problem, have you checked compression? and if you moved your timing, your screwed, the only way to set it is with a tech 2 scan tool, or maybe ther is aftermarket ones that do it, but i dont know... you neeed to check comression, then if that is ok then you need to take it somwhere that has the right tools to set the timing... then check if you have injector pulse on cyl #2????

atboley · September 30, 2007

sorry, stupid computer!!!!!!

GMTRUCKTECH · September 30, 2007

Check your compreesion on that cly. Should be around 150. To realign your dist you can get a mirror and look at the base of the dist and the back of the intake where the dist goes. There is a yellow line on the intake and dist base just line it up and your done. Also injector thats sticking could cause a misfire and assuming you did the tune up right I would check the injector 1st then do a compression test

TBuzz · October 1, 2007

Thanks to all for insights.

GMTRUCKTECH:

Much appreciate the distrib. alignment advice. Will align ASAP.

Q1: Will/can distrib. misalignment result in P0302? As PCM controls timing/advance/retard, it would seem a stretch that this would result in consistent DTC associated with a single cylinder.

Q2: I have Scanpro 5.1 scan tool. Not very proficient with it yet, but...

a. Will single sticking/fouled injector show up in fuel trim?

b. How do I check operation of a single injector?

Q3: It has been awhile (~30K miles) since I've changed my fuel filter. Could insufficient fuel feed result in P0302?

Thanks in advance for great response(s).

I'll keep the forum posted on progress.

atboley · October 1, 2007

Most likely incorrect timing will not set a p0302, you would run into other problems also, but you still need to make sure its set right... a fouled injector may change your fuel trim(may put it at around 10% or more, to compensate for lean condition), but its not the best way to diagnose it, the most accurate way to check the injector would be to pull the fuel rail off and crank the engine, just check to make sure a mist of fuel comes out, you dont want a stream... or you can buy an injector pulser, it plugs into the injector and pulses it for a few seconds and you use a fuel pressure guage to watch the fuel pressure drop and compare it with the other injectors... a plugged fuel filter probably wont cause a 302 either, but if it is clogged it would cause very high fuel trim readings...

BTW, if your scanner shows an option for CMP RETARD, that is your ignition timing reading, set it to as close to 0 as you can...

blue-ss-camaro · October 1, 2007

... a plugged fuel filter probably wont cause a 302 either, but if it is clogged it would cause very high fuel trim readings...

But wouldnt it cause a lean condition which is the cause for that code? I was also thinking maybe a weak fuel pump or weak fuel pressure regulator maybe????

atboley · October 2, 2007

a p0302 is a cylinder #2 missfire, so saying that a lean condition would cause just cylinder #2 to missfire is unlikely...

a lean condition may set a p0300(multiple or random cylinder missfire)...

he did say there is an occasional p0300 setting, but if you have a dead missfire on a single cylinder it may cause the next cylinder in the firing order to register missfires(called a simpothy missfire), when the next cylinder is not actually missing... and im guessing thats why there is somtimes a p0300 setting... a weak fuel pump would also cause high fuel trim readings just like a clogged fuel filter, but not a single cylinder missfire... a leaking pressure regulator would cause a missfire, but you would also have long cranking times, but it would cause a rich condition and you would have -% fuel trim readings

blue-ss-camaro · October 2, 2007

a p0302 is a cylinder #2 missfire, so saying that a lean condition would cause just cylinder #2 to missfire is unlikely...
a lean condition may set a p0300(multiple or random cylinder missfire)...

he did say there is an occasional p0300 setting, but if you have a dead missfire on a single cylinder it may cause the next cylinder in the firing order to register missfires(called a simpothy missfire), when the next cylinder is not actually missing... and im guessing thats why there is somtimes a p0300 setting... a weak fuel pump would also cause high fuel trim readings just like a clogged fuel filter, but not a single cylinder missfire... a leaking pressure regulator would cause a missfire, but you would also have long cranking times, but it would cause a rich condition and you would have -% fuel trim readings

I dont mean to highjack your thread tbuzz Just trying to solve this problem..... I checked compression on cyl 4 which is the one that always comes up on the code and it was between 160-165. so thats fine Plug looked a little white which indicate a lean condition. now I also notice that sometimes it take alot of crank time to start the truck. mainly when it sit for awhile. you said this might be a regulator problem. where are the regulators on the 5.7. maybe that could be cause my misfire???

atboley · October 3, 2007

regulators on the 5.7's are under the upper plennum, they are attatched to the fuel injector assembly... you should start by checking your fuel pressure tho, hook up a fuel pressure guage and key on the ignition, the fuel pressure should climb up to around 55 and it should hold, if it drops quickly then that is a problem, you could have your regulator leaking or a fuel pump leaking, if it holds then there is no problem with your regulator or pump... a leaking regulator will cause it to run very rich and will cause most all the cylinders to missfire...since you said the plug was white, i would tend to say you more likely have an injector problem. those motors have huge problems with the injectors sticking and being clogged, it will cause a dead missfire most of the time,(here in california they are coverd under warranty for 10 yrs or 100000 miles, because of our bad gas), but other states also have the same problem...without the proper tools there is no easy way to diagnose a plugged injector, so it just depends on how much money your willing to spend on throwing darts...

a new set of injectors comes with a new regulator, so you could eliminate both those posibilities at once if you go that route...

TBuzz · October 6, 2007

All... Thanks for continuing interest/input. My apologies for slow turnaround

Pls note that this vehicle has 233K miles and has been a great truck. I realize that it's old but other than the CEL it's very reliable. The urgency for resolving the problem is passage of Texas Emission Controls Test to maintain legal sticker.

I have adjusted distributor position (no change to P0302 as expected) and changed fuel filter (again no change). I haven't checked compression on #2 however I did have compression checked all around about 6 months ago.

I believe I'm now down to fuel injector/injection-related root cause. This is hard to believe as I had a complete set of new injectors installed by GM ~8mos. ago.

I unplugged and replugged the gang connector to the injectors to insure I didn't have a bent/corroded pin... nothing noticeable and no change after re-connection.

I'd be very interested in how I can check out the #2 injector (only) to see if it is misfiring without unbuttoning plenum, etc.
I've attached a graph from my scantool of short-term and long-term trim for bank #1 & #2. This is 30 seconds including one rev up and back to idle. It looks as though:

- the absolute % levels between banks are significantly different; and
- that there is a coarseness to the changes in levels in #2 that is more smooth in #1.

Could anyone pls help me interpret the meaning of these? Or advise what alternative traces would be helpful in further diagnosing this persistent #2 misfire?

Thanks,

TBuzz

ST___LT_Fuel_Trim_Banks_1___2.pdf

atboley · October 7, 2007

if you are dealing with a pluged #2 injector the fuel trim is not going to show anything that would help... it looks fine... what you can do, hook up a fuel pressure gage, key it up and make the fuel pressure rise, and connect power to the pink wire, and ground to the light/green-black wire goign to the #2 injector with the connector disconected, hold it there for about 3 seconds, do this for every injector... watch for the fuel pressure drop, it should be the same for every injector... if #2 is plugged it will be much less of a pressure drop than the rest... this is a flow test and it will test how much fuel the injector will flow... this may be a difficult way to ddiagnose but it is the only way... otherwise check the compression, if that is ok than jsut replace the injectors... since it was only 8 months ago they may still be under warranty...