93 civic backfiring

[T2urtle]

A coworker of mines is having trouble with his civic. Its a 93 vtec, automatic model with 150k. It starts and moves pretty decent.

His problem is when it isn't warmed up, it would backfire at RPM above 2.5k randomly. Really nasty poping noises and somewhat chunging. Its a lot better once warmed up.

Common sense was to start with a simple tuneup. He told me he did the cap and rotor a while back ago but he moved the distributor, so i think he screwed up the timing hence why the backfire on colder engine.

He has done air filter, cap, rotor and now plugs and wires. Will be doing a fuel filter shortly and i'll help me check out the ign-timing.

 

[nismotigerwvu]

Has the oxygen sensor ever been replaced?

 

[T2urtle]

I would say NOT. Owned the car for 2 years, i took a quick glance during lunch to see if anything was simple like vaccum leaks or insane oil leaks.

I'm not used to older stuff. Would a o2 sensor cause a backfire, i was thinking this would be more on timing of the engine.

 

[nismotigerwvu]

Well I can't think of any cases offhand where I KNEW an O2 sensor was directly causing backfiring, but since they can lead to to improper air/fuel ratios it might be a factor. Considering it is a cheap and easy thing to try, it might not be a bad idea.

 

[Harrod]

Have him unplug his throttle position sensor and start it up and see if it goes away when he starts it. I ran into a problem very similarly when I did my swap in my integra, it turned out to be the problem. Also there is an oring under the map sensor that could be causing the map to read incorrectly, not sure that this would be a problem, but since he checked everything else it would be the next thing I would look at.

 

[twinrider1]

Is this out the exhaust or the intake?

 

[T2urtle]

Have him unplug his throttle position sensor and start it up and see if it goes away when he starts it. I ran into a problem very similarly when I did my swap in my integra, it turned out to be the problem. Also there is an oring under the map sensor that could be causing the map to read incorrectly, not sure that this would be a problem, but since he checked everything else it would be the next thing I would look at.

He didn't check everything. I took a quick glance over to make sure all vac lines are not missing/broken/dry rotted. I couldn't read the plugs because he just put new ones in.

Will look into this TPS.

 

[alkalinetaupehat]

Check the distributor/timing since that's easy and go from there.

When did the problem start and did anything change/happen with the car at this point? (e.g. maintenance)

 

[dfanatic86]

if he took the cap off, did he reconnect the plugs in the correct order?

 

[funboy6942]

Timing belt is worn out/stretched throwing the timing off and the back fires. Fix it before it totally goes and takes valves with it, if its not a clearance free motor/head.

 

[Howard]

Timing belt is worn out/stretched throwing the timing off and the back fires.

You can inspect for missing teeth.

 

[funboy6942]

I dont know about missing teeth but backfiring and chugging are signs of the belt being stretched to the point its about to give out. At 100K+ miles it needs to be changed anyway, they dont last forever.

 

[T2urtle]

how hard are belts on these Honda?

I've done a single ohc belt on a Mitsubishi not too long ago, motor mount removed and everything was butter smooth in like 4 hours. Never did Honda's and they are wierd to me as they are flipped around. I'm used to belts on the pass side.

 

[dfanatic86]

Not all that diff from Mitsubishi. Jus for peace of mind I'd change the water pump while your in that area. And don't lose the key way. Good luck.

 

[natto fire]

Check the distributor/timing since that's easy and go from there.

When did the problem start and did anything change/happen with the car at this point? (e.g. maintenance)

This first. Did the symptoms start roughly after he did the tuneup, and "moved the distributor"? Don't get a step ahead of yourself and worry about sensors and belts. KISS.

Timing lights are relatively cheap and a lot easier to use than pulling the valve/front cover apart and checking the cam/belt for damage (is this a D or B motor?). If timing light shows timing is off, simply adjust it into spec. If it is erratic at idle, then that is a good time to start looking into sensors or the igniter.

As far as the timing belt, when was it last replaced? Some people change them religiously at 60-75K, others are more lax. Definitely not an engine you want t-belt failure on, that's for sure.

 

[hanoverphist]

how hard are belts on these Honda?

I've done a single ohc belt on a Mitsubishi not too long ago, motor mount removed and everything was butter smooth in like 4 hours. Never did Honda's and they are wierd to me as they are flipped around. I'm used to belts on the pass side.

they arent terrible to do, but there is a bunch of space limitations. youll definitely want to find the 50mm pulley tool also, the first time i didnt have one and used load straps to keept it all in place, but it was a challenge.

i dont think its the timing belt tho, i bet its more the dist/ timing or the tune itself.

when is it backfiring? during deceleration or acceleration? what motor is it? B and D series are similar, but have differences.

 

[BUTCH1]

I dont know about missing teeth but backfiring and chugging are signs of the belt being stretched to the point its about to give out. At 100K+ miles it needs to be changed anyway, they dont last forever.

Yea, that's where I'd look at if it's the original belt from '93 then it HAS to be on it's last legs..

 

[T2urtle]

Its a d series motor.

I couldn't find the plug to get base timing ( i must be blind) but I adjusted the distributor to the middle and sent him on his way to report to me later.