1985 454 CRUSADER My headache

[dockknocker]

in a trojan 10 meter and my problem is:<br />Port engine at 1400 to 2200 rpm I get a backfire through carburator and very rough engine performance in this RPM range. Engine idles smooth and starts right up runs great above 2200 rpm. Here is what I have done.<br />New fuel pump , new fuel lines, fuel and water seperator, new carb, installed petronix II electronic iginition ( 2nd module because I thought the 1st one was bad). Things I have not replaced. My dist cap and rotor are 3 years old look ok. Spark plug wires are from 1998 and are the Magstar wires. Could the wires be bad?<br />I also had the fuel line pickup blown out approx a year ago for this engine due to stalling that seems to have stopped. <br />Sorry for the long post but I am stumped and running out of asprin. <br />All suggestions appreciated.

 

[Wart T]

Re: 1985 454 CRUSADER My headache

Man, it seems you have eliminated most of the things I would think of at first. I doubt it is the wires because ignition problems usually occur across the entire range. If a plug wire is bad it will be bad at idle and at speed. So I dont think it is the cap and rotor. Your advance mechanism has been replaced and the problem still persists.<br />Lets try not replacing anymore parts until you can get some sort of lead. It's time to back up and re-group.<br />Try looking for a vacuum leak around the intake manifold gasket. Spray WD-40 around it and see if the engine rpms change. Just to be sure, verify the firing order is correct. I believe it probably is but no harm in checking. No harm in doing a compression check too. You have to re verify all the basics first and fortunately that is mostly free.<br /><br />One question, does it continue to run badly if you maintain rpm in the bad range? <br /><br />If possible, hook up a timing light to a plug wire and have someone watch what happens as you drive through the bad range. Does the light flicker and become intermittent? If so the problem is probably electrical. If not it's something else.<br /><br />The fact that it runs well at speed shows fuel delivery is probably okay. What kind of carburetor is on it? If it is a Rochester you can try a restrictor plate adjustment, your symptoms don't really match up with that. But it's free.

 

[dockknocker]

Re: 1985 454 CRUSADER My headache

Thanks for the reply, When the engine is 1st started I don't have this problem. Say it sits over the week and I start it on Saturday am runs fine until we run for approx 15 to 20 min then starts this. If I cove out for several hours I will have the problem. So I guess it will not screw up untill the engine is warmed up and stays warm. It has a Rochester 4bbl Carb.

 

[dockknocker]

Re: 1985 454 CRUSADER My headache

Well I had to get a mechanic and we did a compression check with R&R spark plugs and it is fixed. That was an expensive spark plug!<br />Thanks for the response.