Randomly loosing all power, and then randomly getting it back again.

[jcerecke 2]

Hey,

So this has been happened for aaaaaaages to my '85 320i, but I've just never gotten around to doing anything about it.

I've read up a couple of posts on e30s cutting out etc while you drive, but mine doesnt cut out altogether. It just looses all or most of it's power.

Pretty much I'll be going along, and then suddenly revs drop off to idle and car starts to slow down, and so I take my foot off the gas and put it back on, revs surge to 2K-ish, and then drop down to idle. I pull over. Stationary it does the same thing (usually). So I just sit there and try revving the engine every 20s until it fires back up. And it usually does after 2-5mins.

BUT... I've tried and tried and tried and can not find any constant in terms of when it does it, and what I may or may not do to get it going again.

Usually when it fires back into life it's fine again for another couple of weeks... sometimes it's not. Sometimes I have power up to about 4k driving along (but quite sluggish), sometimes I have no power (above idle). Sometimes it happens in the rain (more often than not), but it has also happened 2hrs into a drive over arthurs pass. That time it was sluggish and ran to about 3.5K all the way back, and loosing all power completely at times (back to idle) which is where I would pull over and wait, and then it would be right again after a while but only to about 3.5K which it would just refuse to go over.

Today it happened again! Well actually it happened yesterday but it happened again today too. I thought (silly me) that it could be a damp distributor cap, so it pulled it off and gave everything a wipe down, and had such a mission getting it back on (screw driver was just not long enough haha). But that didn't change a thing. I did notice though that if I slowly eased up the throttle the revs would climb and sit at about 2k, and then if I kept pushing it (while stationary) it would go back to idle speed. I tried flooring it and it would sort of start to climb (assuming to 2k) and but before it could get there I had already given it too much gas and it dropped off to idle again, so I kept my foot flat on the throttle, and it would jump up to 2k then straight back down, and then 2seconds later, do the same thing, over and over.

There was one occasion where it would rev completely normally all the way up to as far as I wanted to push it (6ish-K) while stationary, but as soon as it was under load (moving) it would struggle to get above 2K.

Everytime it has happened though (bloody murphy) it has been outside of my mechanics operating hours, or I have been nowhere near his workshop (like arthurs pass), or on the way to his workshop it comes right and it's back to 100% fine again.

I didn't really care before because it would always come right, but now it's starting to become a real pain in the arse.

I'm not that mechanically minded so go easy, but I am also keen to learn new things.

Cheers for any insight... at all... anything.

[euroitalian 62]

If your car has Motronic ignition (Disy on front of head) it may be the engine management sensor (Blue/Green 2 pin sensor in thermostat housing) They should have approx 2.9K ohm resistance across the terminals when cold, and this should drop as engine temp rises.

[sp8s 1]

Sounds like its the thingy that connects to the doofer

Seriously, sounds like fuel starvation to me but expert Glenn will call in soon

[*Glenn* 854]

I'd also check the vane inside the AFM and make sure it is smooth in operation and doesnt stick. These can be quite sensitive to differences in temperature. Could also be a loose baffle in the muffler which blocks the exhaust occassionaly. You would notice this though as the exhuast note would be different. Its something that you really need to check when its doing it though. It could be a number of different things and we could all give opinions and alot of the opinions would end up being wrong. Intermittent faults like this can be barstards on older cars as they have very limited fault code memory.

[jcerecke 2]

Also thought I'd mention if I floor it while it's doing it's thing, it sounds sort of like it's backfiring, except it's not very loud... not really sure how loud it's meant to be though. But it definitely comes from the exhaust. Just goes pop... pop pop... pop.

[dirtydoogle 383]

As glenn said, it could be quite hard to find, but, keep it simple. Sensors, fuel pressure when that happens, earthing on all components? Any sad looking wires...blah blah....

[*Glenn* 854]

Also thought I'd mention if I floor it while it's doing it's thing, it sounds sort of like it's backfiring, except it's not very loud... not really sure how loud it's meant to be though. But it definitely comes from the exhaust. Just goes pop... pop pop... pop.

From what you have now said leads me to believe its the exhaust that is blocked by a loose baffle causing the engine to exhaust into the inlet manifold due to the back pressure caused by the blocked exhaust. However I could be wrong.... others will give their opinions, but its a bit hard to diagnose on the internet.

You never know... it might even be your headgasket ... you never know... that might also be given as an opinion.

I realy suggest you continue with getting it checked professionaly when it does play up to prevent wasting good money looking for a peblem that may not exist

[Mark 178]

Take it to DCH Motorsport... Graham Clyde knows everything about E30's.

Lot's of local members cars are regulars there.

[kerry 10]

graham is a old friend of mine and he is really good on e30's, my 2c is the airflow meter, its a common fault!

[jcerecke 2]

I'd also check the vane inside the AFM and make sure it is smooth in operation and doesnt stick. These can be quite sensitive to differences in temperature. Could also be a loose baffle in the muffler which blocks the exhaust occassionaly. You would notice this though as the exhuast note would be different. Its something that you really need to check when its doing it though. It could be a number of different things and we could all give opinions and alot of the opinions would end up being wrong. Intermittent faults like this can be barstards on older cars as they have very limited fault code memory.

So I replaced the fuel filter because that was the easiest thing I could do. Nothing changed...

Now if it was the blocked baffle, could I unbolt the muffler and try to run the car and see if it makes a difference? At the moment it seems like the intermittent problem is not so intermittent anymore. I noticed that when I increase the throttle, theres a little piston-like thing that moves in and out... just wondering what it is, and whether it's moving at the right time. I took a video of it to show what I mean.

Also the backfiring noise sounds like it's coming from the engine bay somewhere, not the back of the car. (which I'm going to assume also points to blocked baffle).

Anyway, can I just unbolt the thing and see what happens? and is it possible to screw that up? haha.

Cheers for all the suggestions people. I tried to shoot into DCH Motorsport last week but we're flatout at work at the moment and next week.

[*Glenn* 854]

Thats the throttle damper which is working properly. The miss firing sounds like cross firing in the distributor cap. Have you fitted an new distributor cap and rotor ? New ones? You can unbolt the exhaust just to check, or if your car has an oxy sensor, just remove that to try.. it will allow enough exhaust to escape to try it and less hassle.

[Guest FrantiC]

From what you have now said leads me to believe its the exhaust that is blocked by a loose baffle causing the engine to exhaust into the inlet manifold due to the back pressure caused by the blocked exhaust. However I could be wrong.... others will give their opinions, but its a bit hard to diagnose on the internet.

You never know... it might even be your headgasket ... you never know... that might also be given as an opinion.

I realy suggest you continue with getting it checked professionaly when it does play up to prevent wasting good money looking for a peblem that may not exist

Wowww someone is funny.

Could be something as lame as a bad coil or rotor/dizzy.. Check everything is plugged in properly esp the vacuum lines to the dizzy.

[jcerecke 2]

Thats the throttle damper which is working properly. The miss firing sounds like cross firing in the distributor cap. Have you fitted an new distributor cap and rotor ? New ones? You can unbolt the exhaust just to check, or if your car has an oxy sensor, just remove that to try.. it will allow enough exhaust to escape to try it and less hassle.

About a year ago I took my car to the west coast and had it parked next to the ocean for a couple days with it pouring with rain at the same time and when it came time to go I couldnt start it. Somehow I eventually got it going and took it to the mechanics when I got back and he found one of the sparkplug leads had a hole in the insulation and was arcing to something so he overhauled the whole ignition system and replaced all the leads, and distributor cap, I think maybe he did the plugs too, but I'm pretty sure he left the original rotor. Will try and look for the invoice to double check.

The other day when I took my distributor cap off to look for moisture I found the clips didn't really seem to fit snugly in anywhere, but none the less I got it seated and firmly attached so didn't think much of it.

It's possible (not sure how likely) but definitely possible that I first noticed this happening not long after one of my visits to the mechanic. But as it's intermittent I couldnt really pin it to him.

[Guest FrantiC]

About a year ago I took my car to the west coast and had it parked next to the ocean for a couple days with it pouring with rain at the same time and when it came time to go I couldnt start it. Somehow I eventually got it going and took it to the mechanics when I got back and he found one of the sparkplug leads had a hole in the insulation and was arcing to something so he overhauled the whole ignition system and replaced all the leads, and distributor cap, I think maybe he did the plugs too, but I'm pretty sure he left the original rotor. Will try and look for the invoice to double check.

The other day when I took my distributor cap off to look for moisture I found the clips didn't really seem to fit snugly in anywhere, but none the less I got it seated and firmly attached so didn't think much of it.

It's possible (not sure how likely) but definitely possible that I first noticed this happening not long after one of my visits to the mechanic. But as it's intermittent I couldnt really pin it to him.

The early style dizzy and cap are a bastard to get on right. Are you sure it's on properly ? It has like a lip IRRC so it has to sit on the dizzy properly then you just hold it down, Push the screw down and turn it to lock it on, and same for the other side.

I agree the popping sound does sound like arcing, And if it got worse after you touched the dizzy that could be a clue you may be looking in the right place...

[jcerecke 2]

The early style dizzy and cap are a bastard to get on right. Are you sure it's on properly ? It has like a lip IRRC so it has to sit on the dizzy properly then you just hold it down, Push the screw down and turn it to lock it on, and same for the other side.

I agree the popping sound does sound like arcing, And if it got worse after you touched the dizzy that could be a clue you may be looking in the right place...

I just took it off again and using a longer screwdriver this time played round with seating it in the right place, and now it seems to be right as rain! I can't believe it would be something that stupid, but maybe it was not on tight before and some jolts from driving moved it slightly so it would start playing up... but I'm not sure how it would then right itself again. But oh well. Thanks all! I've learnt a bit from this so it hasnt been a complete waste of time.

[Guest FrantiC]

Good to hear man, Glad it worked out.