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Rough Idle, dies on slight throttle - with video for diagnosis.

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Mamod17
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Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Wed Dec 26, 2018 5:19 am

Seasons greetings!

Well yet again I have interfered when no interference was necessary. My car has started reliably for 4 years. Recently my my mechanic gave me a lecture about fuels. I normally use 98 octane premium unleaded. He suggested using a lower octane for my older, lower compression engine, so I gave 95 unleaded a go. For good measure I added an injector cleaning additive. #-o Anyway, no problems at first, then I got stuck while out. Super rough idle on turnover and wouldn't want to rev, just wanted to bog, as per video, but I managed to get enough revs to eventually clear whatever the problem was and get home, no probs.

Then I went to start it a day later, same issue. Managed to get enough revs by feathering the throttle - it cleared again, but took longer. Today I tried again and have not been able to get any traction.

Here's what it looks/sounds like on video. It idles around 500, I can take it no further than 1000rpm before it bogs and tries to stall.

https://youtu.be/d71_Tic1l3U

So I've read what I can on the forums and assume it could be any or all of these issues below - or none at all:

My take on the video is that its not a 'one injector' issue: that would run rough but not completely bog. This problem is like it's being choked when slight accelerator pedal is applied.

It could be a blockage of the fuel filter, letting enough fuel through to turn over, but not take any load.

One of the fuel pumps could have died.

I'm assuming all of this because of messing around with the fuel is what was most recently different about the car.

Prior to that a second hand air-con pusher fan was installed (but failed), and will be replaced when I'm back on the road. An air conditioning hose was also replaced and the system re-gassed. Not sure any vacuum hoses could have been affected?

Assuming its fuel, how hard is it to change the fuel filter and fuel pumps. Would you recommend the Walbro fuel pump upgrade? Any links would be most appreciated.

Thanks for your help! [-o< [-o<
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Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Fri Dec 28, 2018 10:12 pm

Changed both fuel pump relay and fuel filter. Got it started and revved beautifully in the driveway, reversed up the hill ok, and down the road 5 meters. Tried to go uphill hand it started hesitating and running super rough. Managed to wake the neighbours and get yelled at trying to keep the revs up. Will look at fuel pressure regulator next.
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miklilmag
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by miklilmag » Sat Dec 29, 2018 6:33 am

Hello,
More diagnostic is needed.
You can do a pressure check on fuel system.
I have seen same symptoms with different reasons, like catalic converter failing, screen clogged on in-tank pump or one of the pump's broken, fuel filter clogged, coolant temperature sensor (CTS) failing.

Also, ECU just wet (my first guess during watching the video) not that difficult to take out and split open.

Good luck
Franke

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sharkfan
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by sharkfan » Sat Dec 29, 2018 7:01 am

I had near identical symptoms which I eventually discovered was a blocked screen on the in-tank pick up; I figured it out after buying and fitting a temporary fuel pressure gauge. I had also previously suspected and changed the fuel filter and pump.

Taking out the in-tank pick up and cleaning it only took 20 minutes but I did make sure I had a new gasket in case it broke.
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Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Sat Dec 29, 2018 7:37 am

miklilmag wrote:
Sat Dec 29, 2018 6:33 am
Hello,
More diagnostic is needed.
You can do a pressure check on fuel system.
I have seen same symptoms with different reasons, like catalic converter failing, screen clogged on in-tank pump or one of the pump's broken, fuel filter clogged, coolant temperature sensor (CTS) failing.

Also, ECU just wet (my first guess during watching the video) not that difficult to take out and split open.

Good luck
Franke
Thank you Franke, I will check what you mentioned. It has been quite wet here over the last few weeks.
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Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Sat Dec 29, 2018 7:39 am

sharkfan wrote:
Sat Dec 29, 2018 7:01 am
I had near identical symptoms which I eventually discovered was a blocked screen on the in-tank pick up; I figured it out after buying and fitting a temporary fuel pressure gauge. I had also previously suspected and changed the fuel filter and pump.

Taking out the in-tank pick up and cleaning it only took 20 minutes but I did make sure I had a new gasket in case it broke.
Thanks Sharkfan, I'll work through the process...will track down a gasket first...
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Brucey
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Brucey » Sat Dec 29, 2018 9:57 am

the other thing that might have happened is that that new fuel/injector cleaner has caused deposits inside the fuel lines to be softened/released. This could have blocked any filter, including the tiny ones on the back of the injectors themselves.

BTW from 6/87 onwards 635CSi was fitted with M30B35 engine; this is known as the 'world' engine and is designed to operate on 95 RON fuel. Earlier (non-cat) M30s will usually run OK on 95RON fuel but were ostensibly designed to run on 98RON fuel.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Sat Dec 29, 2018 11:19 am

Brucey wrote:
Sat Dec 29, 2018 9:57 am
the other thing that might have happened is that that new fuel/injector cleaner has caused deposits inside the fuel lines to be softened/released. This could have blocked any filter, including the tiny ones on the back of the injectors themselves.

BTW from 6/87 onwards 635CSi was fitted with M30B35 engine; this is known as the 'world' engine and is designed to operate on 95 RON fuel. Earlier (non-cat) M30s will usually run OK on 95RON fuel but were ostensibly designed to run on 98RON fuel.

cheers
Thanks Brucey, mine's a 7/86 build M30B34 - I'll be sticking to 98RON from now on! I'm also going to look at the fuel pressure regulator. Occasionally the motor will rev perfectly for a few seconds, then completely lose t sh!!t. So I assume its a line blockage not injector? It definitely won't go uphill, but will drive slowly but more smoothly on about zero throttle on the flat.
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Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Tue Jan 01, 2019 11:58 pm

After a bit of sleuthing with part numbers and finally checking my part number, it seems I was running a 2.5 bar instead of what according to my VIN number should be a 3.0 bar FPR.

Anyone know what difference that would have made? I definitely have a blackened inner exhaust. (running rich?) Haven't checked the plugs. And the oil blackens pretty quickly.

I'm replacing it with a proper 3.0 bar FPR. Hard to find new at short notice so going with a second hand one for now, with the expectation it will fail again at some point. Can anyone recommend a suitable alternative? Perhaps an adjustable FPR - they seem to be much more plentiful?


FYI

Vin No: 1886053

BMW Numbers
13531711541
13531722040

Bosch Numbers
0 280 160 248. 2.5 bar
0 280 160 249. 3.0 bar


Current failed part:
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by 86_6series » Wed Jan 02, 2019 12:06 am

Haven't installed this yet, the inter graded gauge sold me.

https://www.ebay.com/itm/401359217522

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Brucey
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Brucey » Wed Jan 02, 2019 12:11 am

it would have been running lean (open loop) with a 2.5bar FPR instead of a 3.0bar FPR. This could perhaps be adjusted out at idle but not at part throttle. If the engine runs closed loop (with an O2 sensor) then it ought to run OK (ish) once warmed up.

The exhaust can still go black; if you get a lean misfire, unburnt fuel goes down the exhaust and then may burn (badly) to give soot.

There is always a chance that other stuff has been replaced too; to be sure that a 3.0bar FPR is correct, read off your bosch part numbers for the ECU the injectors, and the AFM; you may not have a matched set.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Wed Jan 02, 2019 4:22 am

86_6series wrote:
Wed Jan 02, 2019 12:06 am
Haven't installed this yet, the inter graded gauge sold me.

https://www.ebay.com/itm/401359217522
Thanks! Will be interested to see how it works out...
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Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Wed Jan 02, 2019 4:24 am

Brucey wrote:
Wed Jan 02, 2019 12:11 am
it would have been running lean (open loop) with a 2.5bar FPR instead of a 3.0bar FPR. This could perhaps be adjusted out at idle but not at part throttle. If the engine runs closed loop (with an O2 sensor) then it ought to run OK (ish) once warmed up.

The exhaust can still go black; if you get a lean misfire, unburnt fuel goes down the exhaust and then may burn (badly) to give soot.

There is always a chance that other stuff has been replaced too; to be sure that a 3.0bar FPR is correct, read off your bosch part numbers for the ECU the injectors, and the AFM; you may not have a matched set.

cheers
Thanks Brucey, I will check. I believe the injectors were upgraded and the ECU chipped by the PO...
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Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Sun Jan 06, 2019 4:51 am

Update:

3.0 Bar FP regulator installed - part number correct for my VIN.

No change to situation.

I'll get a fuel pressure tester and check the line into the fuel rail near the firewall.

I assume the fuel pump needs looking at regardless. On a full tank I would smell fuel so I think the gasket needs replacing anyway.
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Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Sat Jan 12, 2019 6:51 am

Good news! I'm up and running.

Replaced Fuel pump relay.

Replaced Fuel pump regulator with 3.O BAR

Didn’t work when I tried the first time but left it a week and it runs perfectly (for now)

Not sure what changed:

Once the FPR was replaced I tried to start it but same symptoms as before. I didn't want to rev it too long as the neighbours wouldn't have been happy.

This morning I pulled the AFM out of the way to pull out a very black spark plug, took photos, replaced.

Checked the new fuse pump relay took it out, put it back in.

Undid the in tank pump cover, had a look - too dirty and no parts to change so replaced it.

Gut feeling told me just to give it a crank again to see what would happen and lo and behold, it started. Took it for a half hour drive - all good.

3.0BAR FPR seemed to be working well. Couldn't really tell the difference in performance.

So I can only think:

Between the fuel filter and engine seems to be ok.

Any further issues would suggest the pump or relay.

It could have been the fuel pump relay and I hadn't given it enough time to pressurise the system

or maybe the relay wasn't seated properly the first time I replaced it...

or moving the AFM disturbed anything stopping it working...

Anyway thank you for all your suggestions. Hopefully it stays this way for a while!

Interested in your thoughts on the spark plug!
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1986 635csi 5speed Alpine White M-Tech Aust Del
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Brucey
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Brucey » Sat Jan 12, 2019 12:57 pm

cause and effect are not easy to discriminate here; poor running causes plugs to go black and sooty but that plug is so fouled that it might in itself cause problems...

A few cold starts and short runs in a row (even with a healthy car) will cause the plugs to go as black as hades like that.

Still don't know if you have a 'matched set' of parts BTW.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Sun Jan 13, 2019 8:42 am

Thanks Bruce,

From the fuel tank to FRP is matched to my best understanding. The head has been worked and I believe bigger mustang injectors were fitted. I'd have to pull everything apart to confirm.

Can still starting and running well so fingers crossed. do you think a conversion to MAF would give me more control?
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Brucey
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Brucey » Sun Jan 13, 2019 2:02 pm

relevant part numbers are all visible without disassembly.


Spending any time thinking about MAF conversions etc whilst you still might have a basic fault of some kind is, IMHO, utter madness.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mamod17
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Re: Rough Idle, dies on slight throttle - with video for diagnosis.

Post by Mamod17 » Mon Jan 14, 2019 10:10 am

I'll keep working on it...part numbers next...
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