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No start / now intermittent start 633CSi

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stever633
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No start / now intermittent start 633CSi

Post by stever633 » Mon Jun 01, 2020 6:26 am

Hi everyone,
I am experiencing a difficult issue on my 1984 633CSi US spec.

It started with a no start after having driven it just a week before. The starter engine would turn just fine but no spark at the coil. Ordered a new coil and just to be sure a new main relay. No luck.

So bought a known to work used ecu. Swapped that out yesterday and after two trials the car would start. Let it run for a couple of minutes and sounded fine, good throttle response. Turned the car off and tried to restart but no go. This cycle repeated itself 3 times yesterday. When the used ecu was attached I moved the wiring harness of the ecu but car kept running just fine.

What could this be? Could the speed or ref sensor be acting up intermittently? When trying to start the tach needle remained flat. The times it did start, the needle jumped a bit before ignition.

I am hesitating to drive it, not confident it would not restart or stall. Hope you have any thoughts on this, thx a lot!

Stephan
1984 633CSi US Spec

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635sharknose
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Re: No start / now intermittent start 633CSi

Post by 635sharknose » Mon Jun 01, 2020 8:06 am

Hoi Stephan,

Have you also tried to start the car again with the original ECU? Are you sure it's broken?
My first guess would be it's a bad contact, maybe a plug connection that makes bad contact. I would at least clean the plugs.
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1987 635CSi Bronzitbeige

stever633
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Re: No start / now intermittent start 633CSi

Post by stever633 » Mon Jun 01, 2020 10:54 am

Thanks for your quick reply.

I was wondering about the ecu as well. I swapped it back and forth 3 times but did not get it running with the old one. But that could have been just bad luck if it is not the ecu to begin with.

This morning tried starting again. Second try started righht up. Was able to repeat this 6 times, no trouble. Did some other stuff, came back after two hours and no luck.

And the tach needle is really the difference: no succesful start when it remains flat. On the ocassion it starts to jump around the start is succesful every time.

To be hones I am not such a handy guy as many of you on the forum. When you say clean plugs and connections, what would be the most likely culprits to start with?

Btw I started this fix by replacing the coil and main relay with new ones. I am still planning on replacing the ref and speed sensor but need to get it done somewhere else. The car is lowered and I cannot reach them from above.

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smtguy
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Re: No start / now intermittent start 633CSi

Post by smtguy » Sun Jun 07, 2020 2:43 pm

Stephan,
When was the last time you replaced the cap and rotor?
1983 Bronzit 633CSi 5 speed
2001 Jaguar XJR
2004 Audi TT

Scott

stever633
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Re: No start / now intermittent start 633CSi

Post by stever633 » Mon Jun 08, 2020 5:36 pm

Hi Scott,

Good one, I have owned the car since 1999 and never replaced it. Thing is that I don’t get a spark at the coil.

Swapped out the coil, main relay and ECU and now the following is happening:
From no start at all I now get a start on the second try when the engine is cold. Every first try the car only cranks but no start. The needle from the tach then remains completely flat. When I try it again right away the tach needle jumps a bit and when it does it always starts. From then on it runs fine, drove it around the block, as if nothing is wrong.

But now it comes. When I shut it down with a warm engine and try to restart I cannot get it to start. Tach needle remains completely flat and no-go. After it has cooled down completely this circus repeats itself.

I am thinking the reference or speed sensor. Could it be that one is faulty when warm? And that it only needs one of these two to keep running after it has started?
Thanks for thinking with me!
Last edited by stever633 on Mon Jun 08, 2020 5:52 pm, edited 2 times in total.

stever633
Posts: 11
Joined: Sun May 17, 2020 3:08 pm
Location: Netherlands

Re: No start / now intermittent start 633CSi

Post by stever633 » Mon Jun 08, 2020 5:50 pm

I have bought the two new sensors (ref and speed) but need to drive it to a shop half an hour away. Not too confident about my theory that it won’t shut down while driving. That was the reason for my question whether it only needs one of these two to keep running.

Other strange thing I thought is that it always needs a second crank to start when cold. So it it an intermittent problem but now with a distinct pattern.

85MSteinway
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Re: No start / now intermittent start 633CSi

Post by 85MSteinway » Mon Jun 08, 2020 7:20 pm

As others have said, check connections in the areas you suspect for good fit and corrosion: coil, ecu etc. cap and rotor sounds like an easy and cheap swap as someone else mentioned. reference the ETM for your car, get a DMM and start probing. check that grounds are solid and test continuity along the way. the fact that its intermittent tells me something is loose or corroded. could be wiring, could be within a component. I'd start with that cap and rotor though.

Jay
L6
85 M635

marc79euro645
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Re: No start / now intermittent start 633CSi

Post by marc79euro645 » Tue Jun 09, 2020 2:30 am

Sounds like the cps, or possible corrosion at connections. An led noid light is cheap at auto parts store. Plug it into an injector lead, crank car. It should flicker with pulse.
good luck

BenM635i
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Re: No start / now intermittent start 633CSi

Post by BenM635i » Tue Jun 09, 2020 7:21 am

If you have the OBC and the factory immobiliser is still connected it could possibly be this.

Mine would do the same, intermittent no spark ... turned out it was the immobiliser which was preventing the spark for random reasons. No pattern to it, sometimes did spark sometimes didn't.
'85 M635 #160

stever633
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Re: No start / now intermittent start 633CSi

Post by stever633 » Tue Jun 09, 2020 7:45 pm

The OBC and imobilizer are still in the car. I removed fuse 27 which should disable the imobilizer but that doesn’t change anything.

Will take it in the shop after the weekend and replace the ref and speed sensor. Hopefully that will make the difference. Found another post on this forum that solved a similar problem by swapping these two.

Will keep you updated as soon as I have an update, thx so far for your advice!

BenM635i
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Re: No start / now intermittent start 633CSi

Post by BenM635i » Wed Jun 10, 2020 7:35 am

stever633 wrote:
Tue Jun 09, 2020 7:45 pm
The OBC and imobilizer are still in the car. I removed fuse 27 which should disable the imobilizer but that doesn’t change anything.

Will take it in the shop after the weekend and replace the ref and speed sensor. Hopefully that will make the difference. Found another post on this forum that solved a similar problem by swapping these two.

Will keep you updated as soon as I have an update, thx so far for your advice!
Dropping you a PM mate.
'85 M635 #160

stever633
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Re: No start / now intermittent start 633CSi

Post by stever633 » Tue Jun 16, 2020 6:29 pm

Hi Ben,
Thx, that would be great. I am a newby, cannot find the PM box...
Thx, Stephan

BenM635i
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Re: No start / now intermittent start 633CSi

Post by BenM635i » Wed Jun 17, 2020 7:44 am

stever633 wrote:
Tue Jun 16, 2020 6:29 pm
Hi Ben,
Thx, that would be great. I am a newby, cannot find the PM box...
Thx, Stephan
Sent you a PM the other day, your message box should be top right of the screen (just under search bar on mine anyway). If the sensors didn't fix then may be worth trying the immobilser avenue.
'85 M635 #160

stever633
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Location: Netherlands

Re: No start / now intermittent start 633CSi

Post by stever633 » Wed Jun 17, 2020 4:58 pm

Ben, thx. Sent you a pm back, let me know if you didn’t get it

stever633
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Location: Netherlands

Re: No start / now intermittent start 633CSi

Post by stever633 » Wed Jul 01, 2020 2:28 pm

Well guys, the mystery of the no and intermittent start has been solved. I had it transported to my mechanic 60 miles away. He took his time figuring it out. Started with replacing the speed and reference sensor but no luck. Then checked the pulse from the brandnew reference sensor when cranking the engine and guess what. No pulse! Since this guy has been working on 6-series when they were still brandnew he remembered that he saw a reference pin coming loose from the flywheel before. Removed the sensor and indeed no pin in the flywheel. Loosened the transmission and the pin was in the bellhousing. He pressed it back in with Loctite and all good again! Just got back from the 60 miles trip, touched the 100 mph and man it runs great! Thanks for your advice, has been helpfull narrowing it down!

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635sharknose
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Re: No start / now intermittent start 633CSi

Post by 635sharknose » Wed Jul 01, 2020 4:34 pm

Very nice to hear it is solved! Thanks for letting us know.
To which mechanic did you take it? Always handy to have such addresses.
Instagram: @635sharknose
1987 635CSi Bronzitbeige

stever633
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Re: No start / now intermittent start 633CSi

Post by stever633 » Wed Jul 01, 2020 7:15 pm

My mechanic is in The Netherlands :(

I have lived in the US for 8 years. Bought the car in 1999 and shipped it when moving back to Europe. Maybe not a good economic decission but I cannot part with it.

Getting difficult to get some (US specific) parts such as exhaust, ECU, some trim stuff. But I simply cannot let the car go. Will try to keep it in good shape to give to my small boys.

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635sharknose
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Re: No start / now intermittent start 633CSi

Post by 635sharknose » Thu Jul 02, 2020 4:54 pm

I am too! Den Bosch.
Instagram: @635sharknose
1987 635CSi Bronzitbeige

stever633
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Re: No start / now intermittent start 633CSi

Post by stever633 » Thu Jul 02, 2020 8:38 pm

Haha, what a coincidence. I am close to Rotterdam but take my car to Garage Lubek in Hilversum. He is already retired but works Monday thru Thursday from let’s say 10 am. Great guy.

stever633
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Location: Netherlands

Re: No start / now intermittent start 633CSi

Post by stever633 » Thu Jul 02, 2020 8:41 pm

Maybe we can hook up one time. Was hoping to go to the Sharknose meeting this year but will have till wait until next year.

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