Changed EVERYTHING, Still misfiring.... 97K1500-5.7vortec (stock)

[Archer-97k1500]

This is a long shot but here goes...

got the truck from my uncle when he passed away so I'm trying to keep her alive. I blew the transmission up when I got it so I removed it and had it rebuilt. after installing the rebuilt transmission, the engine started misfiring (at idle and light load). thinking that it was just a cap and rotor, I replaced them (no change). at this time I was getting some O2 sensor codes so I replaced them all (4) no change other than the O2 codes going away... from there I thought wires and plugs! replaced em with no change...

From there I figured I'd look at the fuel system. I already changed the fuel filter during the tuneup so I checked fuel pump pressures and i was getting 56psi. my Haynes manual said I should have 60-65psi. so I replaced the fuel pump suspecting I had a weak pump (no change). so then I started hearing about the spider injectors leaking on most vortec engines so I replaced the spider injection unit and fuel pressure regulator (no change)....

at this point I started to question some of my other engine sensors and wiring... so I verified that my O2 wiring was good, it is. so is my tps, map, maf, iat, iac... etc... everything under the hood was checking out. so I thought, maybe a bad PCM... found one for cheap swapped it over. NO CHANGE!....

So at this point I thought maybe I've got a bad engine... found one for a good price and low low miles, swapped her over and its still doing the same thing... no codes will store and the engine light flashes when running.

ANY THOUGHTS APPRECIATED

Archer

 

[Ironhead]

Just a hunch, but if it pulls strong under load, but misfires at idle and light load, might be a vacuum leak. I'd check the vacuum lines and fittings, including the brake booster, PCV, vapor purge system, etc.

 

[michael hurd]

Sounds like you have changed a lot of parts.

Were you getting a misfire code, or did you 'think' it was misfiring>?

EGR pintle could be stuck. What did your scanner report for the coolant temperature? Did you verify it with an non contact thermometer?

 

[Archer-97k1500]

Just a hunch, but if it pulls strong under load, but misfires at idle and light load, might be a vacuum leak. I'd check the vacuum lines and fittings, including the brake booster, PCV, vapor purge system, etc.

Thanks for the reply. Vacuum booster holds pressure. Verified all vacuum lines are ok. Keep in mind that BOTH engines are acting the same.

 

[Archer-97k1500]

Sounds like you have changed a lot of parts.

Were you getting a misfire code, or did you 'think' it was misfiring>?

EGR pintle could be stuck. What did your scanner report for the coolant temperature? Did you verify it with an non contact thermometer?

Thanks for the reply! The PCM is not storing codes. The only indication that the engine is misfiring is that the engine light is flashing. I have a couple spare egr valves and they all make the engine run the same...

 

[michael hurd]

It may be time to beg, borrow a good scan tool to look at the live data stream to see if there is something you can find via that.

If you have a misfire, it will show up in the live data stream.

I have heard anecdotally that some cheap cap and rotors can fail after just a short period.

 

[Archer-97k1500]

It may be time to beg, borrow a good scan tool to look at the live data stream to see if there is something you can find via that.

If you have a misfire, it will show up in the live data stream.

I have heard anecdotally that some cheap cap and rotors can fail after just a short period.

Im thinking the same thing.. only problem is ill have to goto the dealer. Ive tried those bluetooth dongle to ur phone apps but i dont think its good enough...

 

[96-1500]

Be very careful of the big plug with a million wires going into the top of the spider injector assembly. Go over all the little connections with a fine tooth comb. I had a problem with it once after an engine swap. Took me awhile to figure out what the problem was.

This started right after the transmission was swapped in? Really sounds plausible that a plug or wire got pinched somewhere by accident.

I am assuming of course you used the same wiring harness from your truck after the motor swap.

 

[Archer-97k1500]

Be very careful of the big plug with a million wires going into the top of the spider injector assembly. Go over all the little connections with a fine tooth comb. I had a problem with it once after an engine swap. Took me awhile to figure out what the problem was.

This started right after the transmission was swapped in? Really sounds plausible that a plug or wire got pinched somewhere by accident.

I am assuming of course you used the same wiring harness from your truck after the motor swap.

Thanks for the reply.

I'll double check the spider injector harness connector for damage. I was carefull not to pinch any wiring during either swap but again ill double check that too.

 

[Stepside_fever95]

Before you spend any more money, id check to see if your distributor is off by one cog. Its easy to do, and was my problem when i changed my intake manifold gasket. Theres a thread somewhere on properly setting the vortec distributor.