m50 missing and backfiring intermittently

[JGood]

if you have a spare set of coils to try....definitely do that, at least to rule them out if it doesn't fix it. I'm wondering if you have a bad plug still. I was chasing a misfire in my Ford for a long time, turns out it was a plug that had less than 15k on it.

It was bad enough at times that I had my OBDII diagnostic tool plugged up continuously to reset the CEL and watch engine parameters.

Thanks, I'll try a new set of plugs. They say BMW on them, so I assume they are old. I've had this engine in my car for 30k miles or so, so they at least have that many. But I'm willing to bet many, many more!

have you removed the injectors at anytime?

Nope.

[JGood]

Are the NGK 2288's a recommended plug for this engine?

[nando]

uhm, you can't swap the main and O2 relays. the main relay is a double 87 output. the FP and O2 relays are a single 87 output. you must have swapped O2 and FP relays already. :p

if the plugs are that old, they definitely need replaced. they're cheap enough that I tend to do mine once a year.

[shiboujin]

Get a fuel pressure gauge. Just because the pumps work doesn't mean you're getting good fuel pressure.

Do it. If you blow me off, I will fucking come to your house and CUT YOU. I don't like this "well it gushed fuel when I took the line off" or "I put my thumb on it and it pushed back real hard". Is your fucking finger a pressure gauge? No? Then fucking get a gauge! Fuck. EVERYONE should have a fuel pressure gauge.

Fuel pressure gauge!!

TL;DR -> FUEL PRESSURE GAUGE

[nando]

a fuel pressure gauge is a good idea, but his plugs are definitely toast and they're also cheaper/easier to replace right meow.

[shiboujin]

true but the backfire in the intake isn't conducive to spark plugs. It's more than usually fuel related. I'm saying either one of his pumps is bad/clogged or the FPR is dying.

[e30s50dan]

Bad MAF !? maybe...

[nando]

but a bad pump won't leave fuel in your intake. it would just go lean. ;)

[shiboujin]

a dying pump most certainly will leave fuel in your intake. Atomization will be droplets instead of a mist. Plus if things aren't getting combusted, it goes somewhere. I've seen many cars run lean but leave fuel pooling in the intake.

Also, maybe it's a tps issue? Maf is possible but unlikely.

[JGood]

uhm, you can't swap the main and O2 relays. the main relay is a double 87 output. the FP and O2 relays are a single 87 output. you must have swapped O2 and FP relays already.

I meant I swapped the main and O2 relays with spare relays, off an m20 engine. I couldn't swap the fuel relay because the m20 fuel relay appears to be different then the m50 relay, according to the diagram.

Get a fuel pressure gauge. Just because the pumps work doesn't mean you're getting good fuel pressure.

Do it. If you blow me off, I will fucking come to your house and CUT YOU. I don't like this "well it gushed fuel when I took the line off" or "I put my thumb on it and it pushed back real hard". Is your fucking finger a pressure gauge? No? Then fucking get a gauge! Fuck. EVERYONE should have a fuel pressure gauge.

Fuel pressure gauge!!

TL;DR -> FUEL PRESSURE GAUGE

I will gladly do that after doing some other simple, free things. I never said I have adequate fuel pressure. Just that the pumps are at least turning on.

Bad MAF !? maybe...

Already swapped the MAF, no change.

[shiboujin]

I will gladly do that after doing some other simple, free things. I never said I have adequate fuel pressure. Just that the pumps are at least turning on.

Sorry wasn't bashing you. It's one of those sore spots for me. There have been many many times fuel pressure was a dead give-away as to what the problem was and people shoved money into other things. Must like people love to have AFR gauges, oil pressure gauges, and volt gauges. Might as well have a useful one like fuel pressure.

[jlevie]

Backfiring through the intake is caused by; a) a lean condition, b) cam timing error. The first can be a fuel delivery problem or result from intake leaks. As mentioned by shiboujin you need to check fuel pressure. If a check with the car stationary doesn't indicate a problem you need to see what the fuel pressure is doing when the problem is present (zip tie the gage to a windshield wiper). A smoke test of the intake will quickly tell if intake leaks are a contributor.

[JGood]

Sorry wasn't bashing you. It's one of those sore spots for me. There have been many many times fuel pressure was a dead give-away as to what the problem was and people shoved money into other things. Must like people love to have AFR gauges, oil pressure gauges, and volt gauges. Might as well have a useful one like fuel pressure.

Is there an easy way to read fuel pressure while driving? Can I 'T' into the fuel line and run a hose through the window to a gauge or something? The car only misses every once in a while, so I doubt I'll see a major problem while idling. It goes away completely above 4k or so, so if I'm getting fuel at 7k RPM's and full throttle, something tells me it's not a fuel flow issue.

The problem is mostly noticeable at about half throttle between 1500 and 3500 RPM's. I can drive a few miles, stop and go, and it won't do it. Then all of a sudden it will miss once or twice, then maybe I can go a few miles again, or maybe it will do it a few more times. Very inconsistent. It hasn't been backfiring much at all lately. Maybe on average once a day during my 70 mile round trip commute. Just missing.

[JGood]

Backfiring through the intake is caused by; a) a lean condition, b) cam timing error. The first can be a fuel delivery problem or result from intake leaks. As mentioned by shiboujin you need to check fuel pressure. If a check with the car stationary doesn't indicate a problem you need to see what the fuel pressure is doing when the problem is present (zip tie the gage to a windshield wiper). A smoke test of the intake will quickly tell if intake leaks are a contributor.

Thanks for the info. I remember looking into a smoke test before, but it seems like the quality test machines are expensive and only found at garages. Would probably be cheaper for me to just replace all the vacuum connectors/hoses/gaskets! (Many of which are new)

[shiboujin]

Some gauges have electric senders. otherwise you can just run an extra long fuel line and run it outside of your hood. But intermittent still mean you might have low fuel pressure all around.

Also, I'm starting to suspect your TPS. I didn't read if you swapped that out.