97 5.7 strange itermittant misfire

[alhutto]

This old man needs some suggestions.My 97 C1500 with a relatively new crate engine and fresh ignition components has a strange problem.With the engine fully warmed up the engine will, on occasion, start to severely bog down, misfire and not rev above about 3500 rpm. If you back off the throttle it will return to a fairly normal state. No codes are set during these episodes and if I stop and shut the engine off and restart it everything returns to normal and the engine runs perfect throughout the full rpm range.I have cleaned and applied dielectric to all the PCM connectors and pins and the tps, maf, map, crankshaft sensor , and the knock sensor pins and connectors..It almost seems like it randomly goes into 'limp mode"and when I cycle the engine off and back on everything resets and runs perfect. I guess I could have a knock sensor with an intermittant defect that causes the PCM to retard the timing or some other major sensor doing the same thing. I guess the PCM could have the same type of intermittant problem. The problem occurs about 2 to 3 times a month with no apparent common weather conditions.This is really hard to troubleshoot when there are no codes set. I have not seen this type problem discussed on this or any other forum. I appreciate any and all suggestions.
Al

 

[bluex]

Did you replace the distributor itself? I have seen on here that worn drive gear can cause the miss fies. performance distributors sells a nice aluminum one for 190.

A stuck injector poppet could cause it also. Did you replace/upgrade the spider while the engine was out?

 

[agent319]

I kind of have a similar issue. So I put the timing light on it. I wasn't worried about the timing at this point I was looking for a dead wire or plug. Anyway the way I do it is hook up the timing light to each plug wire and listen. Well I found that 2,1,5,7 would be clicking right along but every now and then it would get a few extra click in it. I don't do it by watching the light I have to put the timing gun up to my ear and listen. Anyway that's what I found out. This started happening about two months after I replaced wires, distributor cap and rotor. Any suggestions.

 

[alhutto]

Thanks for your interest and your inputs. The distributor was replaced when the engine was installed,a napa I think. The fuel injection spider was not up graded when the engine was installed, in fact the spider has about 300,000 miles on it. Could a bad poppet cause a intermittant problem and "reset " to normal after engine shutdown and restart? Your comments in the fuel injector system put a different light on the problem I think I will do some more research on this aspect. Thanks again for your interest and suggestions.
Al

 

[350VortecSSCT]

Id run 93 and race fuel through the motor...30 gallon tank? put 20 93 and 10 gallons of race fuel no higher than 116 octane that cleans injectors and the whole motor out soooo well

 

[bluex]

Ya a bad poppet could definitely be causing it, especially if they got that kinda mileage on them. If the entire ignition system is new, and the fuel pump has good pressure that's where I would be looking.

You could try a new fuel filter to if the pressure looks a little low...

 

[agent319]

But if my timing light is clicking away but has extra clicks in it what has that to do with fuel or stuck injector "poppet"? How are the plugs getting those extra ignition sparks? How could 2,1,5,7 be getting random ignition?

 

[bluex]

But if my timing light is clicking away but has extra clicks in it what has that to do with fuel or stuck injector "poppet"? How are the plugs getting those extra ignition sparks? How could 2,1,5,7 be getting random ignition?

I think yours is more ignition related then. The op has an all new ignition system which is why I think his is fuel system related. Misfires can be caused by many different things. Your timing light could be clicking because its picking up a weaker signal from another plug wire close to the lights pickup.

What brand of parts did you use for your tune up? How old are your plugs and how many miles on your engine. You could have a worn distributor drive gear.....

 

[agent319]

I think yours is more ignition related then. The op has an all new ignition system which is why I think his is fuel system related. Misfires can be caused by many different things. Your timing light could be clicking because its picking up a weaker signal from another plug wire close to the lights pickup.

What brand of parts did you use for your tune up? How old are your plugs and how many miles on your engine. You could have a worn distributor drive gear.....

1998 K2500, 155000 miles and distributor cap, rotor, spark plugs are 4 months old. I haven't change wires in over 50,000 miles

 

[bluex]

Ok, but what brand are the cap, rotor, and wires. vortecs don't like cheaper components here. Does your cap have a vent? If you bought the cheapest plug wires at advance they are definitely crap by now....

You could also get your coil and module checked....