please help cis backfire

[fzr1k]

have in the past posted my problem the last time noone responded. i have an 82 sc 3.0 that just off of idle stumbles and backfires. i have gone through the engine found 4 broken head studs 2 blown head gaskets and a broken intake valve spring . when i got the car it ran great but it ran hot. one day it caught fire but only burnt heater hose and ac belt .when it caught fire it was missing and backfiring. i pulled intake and cooling shroud and found mouse nests around the cyls. then my cdi box fryed so i put a msd 6al ,blaster coil and taylor thunder volt wires on.soon after it began to have the stumble but not right away. i have had the injectors tested they are fine i replaced the wur( which is euro spec for some reason) rebuilt the fuel dist. replaced the fuel pump,o2 relay,o2 sensor checked o2 control box and ground. when you take the oil cap off the car idles slower air box has been checked no cracks. i replaced intake boots.i have replaced the cap and rotor also this car only has 65k on it. after i went through all of this except the fuel pump it ran better but got progressivly worse to the point you cant drive the car as soon as you give it throttle it backfires and pops back through the intake. my vacuum is right about 22hg. if i turn fuel mixture a few turns eather way it will kill the car like you would expect.i bought this car for 9k have about 12.5k in it so i cant eaven sell it to recover my cash.if someone has any idea please help im at my wits end.

[boyt911sc]

Originally Posted by fzr1k

have in the past posted my problem the last time noone responded. i have an 82 sc 3.0 that just off of idle stumbles and backfires. i have gone through the engine found 4 broken head studs 2 blown head gaskets and a broken intake valve spring . when i got the car it ran great but it ran hot. one day it caught fire but only burnt heater hose and ac belt .when it caught fire it was missing and backfiring. i pulled intake and cooling shroud and found mouse nests around the cyls. then my cdi box fryed so i put a msd 6al ,blaster coil and taylor thunder volt wires on.soon after it began to have the stumble but not right away. i have had the injectors tested they are fine i replaced the wur( which is euro spec for some reason) rebuilt the fuel dist. replaced the fuel pump,o2 relay,o2 sensor checked o2 control box and ground. when you take the oil cap off the car idles slower air box has been checked no cracks. i replaced intake boots.i have replaced the cap and rotor also this car only has 65k on it. after i went through all of this except the fuel pump it ran better but got progressivly worse to the point you cant drive the car as soon as you give it throttle it backfires and pops back through the intake. my vacuum is right about 22hg. if i turn fuel mixture a few turns eather way it will kill the car like you would expect.i bought this car for 9k have about 12.5k in it so i cant eaven sell it to recover my cash.if someone has any idea please help im at my wits end.

fzr1k,

For starter I would recommend using a CIS fuel gauge to check your control and system pressures, have the mixture checked using a gas analyzer, have your frequency valve's operation (on/off) checked too. How did you measure your vacuum? It is not easy to find cracks in the air box by just looking. You need to pressurize it and check for leak/s. Keep us posted and we'll get your car running good soon.

Tony

[47silver]

What caused the fire?

first thing i would check is the pop off valve for leakage. The glue bond may have been damaged in the heat. You will still have a good vacuum but it will mess up the fuel quantity. remove it and reglue it.

Second thing i would check is my fuel pressures with a set of gauges, there are a million post on this site as to how to use them and what to look for with out this information you cannot trouble shoot this system.

The 3rd thing i would check is the wiring from every point that connects to the ignition. My 75 has points, i had a wire in the distributor that occassionally grounded to the cam on the distributor and caused backfiring etc. I found this problem when i was installing a pertronix points device the problem was solved.

You had a major fire which may have fused wires, melted connections or damaged insulation. check it all.

The CIS is simple, it needs a good vacuum and you say you have that. Only thing that could be a concern is the popoff valve.

It needs fuel pressure but we dont know what that is so you need to check it.

It needs spark, the msd/cap/rotor are new. That leaves wires or connections that may be shorting.

Do one thing at a time. Post back one thing at a time.

[Aurel]

Have you checked your advance? Where is it set at idle and 5k rpms?
What exhaust system do you have? When I went from cat to cat bypass I noticed more backfiring at decceleration. When you say you have gone through the engine, do you mean the top-end was rebuilt? Did the mice make their nests after the rebuild?

[fzr1k]

mouse nest were b4 top end rebuild i checked fuel pressure b4 and it is ok not sure about flow volume though .fire was caused by a hot engine and excessive oil from leaks no wire damage. ignition wires are new as are connectors. i dont know about timing i dont have a light avail since i moved. i also need to buy cis tester. i do have a bentley manual but it hasnt been much help. i replaced the pump and it didnt change but i think maybe my volume isnt right or the fuel dist is still messed up but it was clean when i reassembled it. thanks for your input and im going to check those things will keep you posted

[fzr1k]

oh ichecked vacuum with the manometer i use to balance my motorcycle carbs. i will have to chec ign wiring and get back. i fogo to mentio that after new wur ad fuel distributr rebuild and top end the car ran better but still had a small hesitation bu it got progressivly worse. also car runs fine atcold start.

[Bob Kontak]

Is your O2 sensor functioning? "A few turns either way" on the CO screw is a monstrous variation. Check your O2 sensor output with a digital voltmeter while it is running. Tap into the O2 sensor with a single 3 foot wire and put the red probe on the on the wire and the black probe on ground. 0.450 volts is at the right air/fuel mixture after it warms up. Rich is higher voltage and lean is lower.

Nail your ignition timing down, also.

Get the tools and eliminate these variables.

[Bob Kontak]

Is your O2 sensor functioning? "A few turns either way" on the CO screw is a monstrous variation. Check your O2 sensor output with a digital voltmeter while it is running. Tap into the O2 sensor with a single 3 foot wire and put the red probe on the on the wire and the black probe on ground. 0.450 volts is at the right air/fuel mixture after it warms up. Rich is higher voltage and lean is lower.

Nail your ignition timing down, also.

Get the tools and eliminate these variables.