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Voltage to fuel relay and random engines stops

 
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bear924  



Joined: 26 Jul 2005
Posts: 81
Location: South West Queensland, Australia

PostPosted: Wed Apr 21, 2021 10:26 pm    Post subject: Voltage to fuel relay and random engines stops Reply with quote

Hi all,

My S2 931 has developed a fault that I'm struggling to solve. In short, my car runs perfectly and then from time to time it just cuts out. Sometimes when this happens I can just restart, other times I need to wait for a couple of minutes and then the car will restart and work fine. Typically I'll get about four hours driving between events .. then when they occur I seem to get a small run. Cut out will occur at idle, cruising or under load .. at the moment is mainly seems random with a slight frequency increase when sitting at stop lights (currently had to push the car through an intersection three times... hoping to avoid a fourth)

During one non starting event I was able to pull the fuel relay and measure the fuel relay voltage signal (the one off the coil) and it was reading about 6V when cranking. The diagram shows that this is a pulsed signal so I thought perhaps this was possibly correct. My question ... is this indeed a pulsed signal, does anyone know what a typical voltage measurement should be?

Things I've done to solve my problem so far:
- Replaced fuel relay (three times - once with my glove box spare and two other times with brand new relays)
- Replaced coil
- Replaced ignition switch
- Inspected plug onto DITC unit.. all good.
- Removed relay board looking for loose wires
- Checked tension on coil signal wires
- Checked motor earths
- Checked fuel pump terminal tightness
Currently waiting to get my multimeter back home and then plan on checking earthing of DITC and fuel relay.

Has anyone any other thoughts on what I might want to check/ do? Has anyone experienced this kind of failure from the ignition unit/ flywheel sensor? Open to any wild ideas as I'm beginning to run out of them.
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924RACR  



Joined: 29 Jul 2001
Posts: 8436
Location: Royal Oak, MI, USA

PostPosted: Wed Apr 21, 2021 10:41 pm    Post subject: Reply with quote

Not certain it's what you're facing, but I did struggle with intermittent fuel pump drop-outs in my S2; eventually realized that the fuel pump fuse was getting CRAZY hot due to poor contacts at the fuse box... rewired around the fusebox to a modern in-line fuse holder for that circuit, and the problem was fixed.

In my case, this would often happen when hitting bumps/frost heaves in the road.

Regarding the signal from the coil - you're not going to be able to meaningfully look at that unless you have an oscilloscope. Merely having a connection is enough.

Note also that the fuel pump relay grounds through the overboost switch on the intake charge tube; if this is flaky at all, it could also cause a brief shutdown of the fuel pump...

Naturally, monitoring voltage to the ignition controller could be helpful too... I found a very inexpensive digital voltage readout from an electronics supply house, designed to be mounted in a panel... I wired it in and stuck it next to my shifter with double-sided foam tape... if you're intelligent about the leads, you could make it plug in anywhere, and monitor it while you're driving... see if that voltage (to the fuel pump, or ignition ECU, or the like) drop out whenever your problem occurs...
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11670
Location: PacNW

PostPosted: Wed Apr 21, 2021 11:18 pm    Post subject: Reply with quote

Is there a way for him to test his crank sensor, if that could be contributing?
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924RACR  



Joined: 29 Jul 2001
Posts: 8436
Location: Royal Oak, MI, USA

PostPosted: Thu Apr 22, 2021 12:08 am    Post subject: Reply with quote

There are resistance tests in the manual for the sensor...
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bear924  



Joined: 26 Jul 2005
Posts: 81
Location: South West Queensland, Australia

PostPosted: Thu Apr 22, 2021 8:57 pm    Post subject: Reply with quote

Thanks for your responses.

Good pointers on the fuse. It was actually one of the first things that I thought was the problem. My fuse wasn't seated that well. After reseating it went well for a little while and I thought I'd fixed it ... till one day. Might just check again though .. it does seem like something silly like this.

Good to know that the fuel relay input is indeed a pulse. I actually own an oscilloscope so I could take a reading .. unfortunately it's mains powered so not much good at my next set of traffic lights.
I have also considered wiring in some permanent voltmeters so that I get real time fault data. I might see if I can purchase some panel voltmeters and rig something up.

I must admit I haven't measured the flywheel sensor however currently have it unplugged and will do it when I get my multimeter over the weekend. Thought is to also check some grounds.

The overboost switch was also a good suggestion. I have my switch removed as I have electronic boost controller (Innovate) running slightly higher boost with a water to air intercooler.

Open to any other thoughts ... intermittent faults are always the worst!
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11670
Location: PacNW

PostPosted: Fri Apr 23, 2021 5:16 am    Post subject: Reply with quote

I presume you know the overboost switch wire needs grounded?
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bear924  



Joined: 26 Jul 2005
Posts: 81
Location: South West Queensland, Australia

PostPosted: Fri Apr 23, 2021 10:04 pm    Post subject: Reply with quote

Yes. The overboost wire is grounded. Have often used this wire as an anti theft device!
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peterld  



Joined: 10 Dec 2006
Posts: 846
Location: Noosa Heads QLD Australia

PostPosted: Sat Apr 24, 2021 8:27 pm    Post subject: Reply with quote

Bear....I had a similar problem years ago.
Turned out to be the wiring INSIDE the plug that connects to the side of the DITC unit......in need of serious resoldering. Intermittent contact at all strange times left me stranded often....painful.
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bear924  



Joined: 26 Jul 2005
Posts: 81
Location: South West Queensland, Australia

PostPosted: Sat Apr 24, 2021 9:33 pm    Post subject: Reply with quote

Thanks Peter. I checked the plug last weekend after scouring the board for ideas. I couldn't find any poor soldering. I might double check again tomorrow though ... certainly seems like a loose wire, just wish I could find the blooming thing.
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924RACR  



Joined: 29 Jul 2001
Posts: 8436
Location: Royal Oak, MI, USA

PostPosted: Sat Apr 24, 2021 9:44 pm    Post subject: Reply with quote

peterld wrote:
Bear....I had a similar problem years ago.
Turned out to be the wiring INSIDE the plug that connects to the side of the DITC unit......in need of serious resoldering. Intermittent contact at all strange times left me stranded often....painful.


Good point - I had this too, very aggravating. Thankfully, that connector is relatively easy to open up and re-solder.

This also reminds me - I found that my crank sensor terminals were rusty at the DITC! Clearly due to either water intrusion or coolant leak from the heater core, when they got corroded they would cause occasional misfires etc. Though it sounds like that's already been checked...
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peterld  



Joined: 10 Dec 2006
Posts: 846
Location: Noosa Heads QLD Australia

PostPosted: Sat Apr 24, 2021 10:04 pm    Post subject: Reply with quote

Initially I thought my issue was loose pins....in that the male pin was not seating tightly in the female receptor, and that was an issue, but on real close inspection the soldering was suspect on pin 12, the brown ground which was intermittently contacting (bumps in the road/accelerating/decelerating/passenger feet!)
Strangely there was also a brown/red wire going to pin 12 (ground), which is not listed in the FSM.
Also worth checking the connections to the starter motor...small wire can be problematic.
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bear924  



Joined: 26 Jul 2005
Posts: 81
Location: South West Queensland, Australia

PostPosted: Sun Apr 25, 2021 7:57 pm    Post subject: Reply with quote

As per my last post I re-inspected the DITC plug as last time I inspected each pin insitu of the plug .. this time I removed each pin and inspected closely. Didn't find any issues here, however must admit it wasn't the best soldering I've ever seen.

I then proceeded point to pointing the ignition and fuel circuits. While poking around I noticed that the small pin on the fuel relay (pin 11 if I recall.. the ground for the signal) was recessed in the relay board. Pushing it in with the meter probe showed that it wasn't locked in place so I removed it, reset the holding clip and reinstalled... problem solved. So if this has been like this for the entire failure time (I've put the fuel relay in and out quite often over the last few months so possible I've introduced this recently) then it would be a prime candidate. Car performed well on a shorter drive today.. will test over the next few weeks and report back.

Hadn't considered the starter motor cable (know the one you mean .. never as secure as I'd like). If that is loose, will that cause the car to stop?
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bear924  



Joined: 26 Jul 2005
Posts: 81
Location: South West Queensland, Australia

PostPosted: Tue May 18, 2021 9:49 pm    Post subject: Reply with quote

So my excitement about finding a loose wire has proven to be ill placed! Took my 924 out last weekend and after operating perfectly for an hour my car cut out while driving down the road. The good part of the cut out was that I had a great run off area and was able to have a good poke around. Bad part of the breakdown was that the car didn't self correct and I had to get it put on the back of a truck. Of course, on my return home, my car started and ran perfectly. grrr.

So my poke around proved that my issues is that I'm not getting power to my fuel pump. Working back to the relay, I have no problem with power to the relay however the signal coming off the coil (the small pin on the relay) is staying at 12 volts when cranking the car, yet the relay isn't energising. My understanding is that this signal shouldn't be a constant 12V, I suspect that the coil actually drops voltage which pulses the relay (in a negative logic type of thing). On the weekend I'll prove this by taking readings of this point when the car actually starts.

I would appreciate if anyone can explain the signal between the coil and fuel relay on a S2 turbo.
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