No start issue

E28 technical advice asked and given! Troubleshooting, modifications and more.
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nautilus
Posts: 35
Joined: Oct 05, 2021 10:30 PM
Location: Champagne-IL

No start issue

Post by nautilus »

For those interested in the history of getting the car running, after being in storage (+ the work done to date) see this thread: viewtopic.php?f=3&t=158488 I've had a couple of good months driving the e28, so this is definitely an annoyance...

Situation:
Drove the car a couple of miles to the post office. Upon pulling into a parking spot, the car appeared to stall. Wasn't 100% sure it stalled as I was just turning the ignition off, so went inside to take care of business. When I came back out, the car wouldn't start - crank but no ignition. Checked engine bay, couldn't see anything wrong, battery was fine and no leaking fluids, so called for a tow (bump/jump starting wasn't an option).

While waiting for a tow (about 30mins later), I tried cranking again and it started up - drove home quickly and it died twice more on the way, but managed to get it into the garage. Car stalled a couple more times in the garage, while I was trying to replicate the issue by working the throttle linkage in the engine bay (revving to 3-4k). Found the vacuum line for the interior temp sensor in the engine bay was disconnected (I believe this can cause a vacuum leak) so reconnected. No change.

Right now, the car will crank and nothing more. I'm wondering if the issue might be related to the Motronic - this seems odd, given it's a new (refurb) unit and I'm not sure it would fail in a progressive way, with the engine cutting out a few times before dying 100%? As always, I look to those with more experience to help get this properly diagnosed.

Issues I've found:
  • There's no spark - pulled a plug and I can't see anything when cranking; per old thread, these are new (<2k miles plugs) and don't appear fouled
  • The fuel injector plugs aren't getting power - I checked 2 of them - this is weird, given the ECU harness shows power to the injectors (see below)?
  • The 87 pins on the main relay aren't getting power (again, see below)
Diagnostics / Testing:
  • Battery is good - it's <1yr old and the car lives on a tender when not in use
  • Fuses are all good and seated properly
  • Ignition coil resistance readings are within spec (0.7 ohms and 5300 ohms)
  • There's voltage at the FI temp sensor
  • Fuel relay has been tested and is good - I've checked voltages and jumpered the pins; I can hear fuel being pumped around

Main Relay:
  • I don't believe the main relay itself is faulty, as I can hear the relay click when plugged in, if the ignition is on.
  • I jumpered without the relay (3 way, 30/87/87) and tried starting with both the fuel and main relays jumpered, no change
  • Further testing showed there's virtually no power (0.72v and 0.03v) to either of the 87 pins; I am seeing 13v to pin 30 and 12.9v to pin 86 when the ignition is on/off; (I've tested from the underside of the connector as well, just to be sure)
  • From reading the ETM, the red/white and blue/red wires from the 87 pins go to the ECU for power, the fuel pump relay and injectors
  • With the ECU disconnected, the ECU harness shows 12-13v power @ pins 35/18 (power inputs), 20 (fuel pump relay control) and 14/15 (fuel injectors)
I don't get how the ECU harness can be powered, but I'm not seeing any power at the injectors? Why the plugs aren't getting spark is also weird, given the ignition coil seems to be working

Let me know if you have any thoughts as to where I can go next
Thanks
1st 5er
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Re: No start issue

Post by 1st 5er »

Crank position sensors checked?
Mike W.
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Location: California Whine Country

Re: No start issue

Post by Mike W. »

My complements, you did some troubleshooting first, not just, "my car won't start" :up:

Shermans suggestion of the flywheel sensors is a good one, but I would start further up. I'm not entirely clear on what's happening, but the power to the main relay, and eventually the injectors and ignition comes off the medium red wire off the battery positive terminal. I'd go there first, remove, clean and replace it. Batteries are prone to corrosion as well as anything right at the terminal, that red wire might not be making a good electrical connection. And sometimes good enough to read off it with a meter, but not good enough to actually do anything. Clean that up and make sure you have power going to the injectors with the main relay engaged.
Kovic
Posts: 40
Joined: Nov 23, 2022 6:32 AM
Location: Rotterdam, The Netherlands

Re: No start issue

Post by Kovic »

Mike W. wrote: Nov 27, 2022 4:26 PM My complements, you did some troubleshooting first, not just, "my car won't start" :up:

Shermans suggestion of the flywheel sensors is a good one, but I would start further up. I'm not entirely clear on what's happening, but the power to the main relay, and eventually the injectors and ignition comes off the medium red wire off the battery positive terminal. I'd go there first, remove, clean and replace it. Batteries are prone to corrosion as well as anything right at the terminal, that red wire might not be making a good electrical connection. And sometimes good enough to read off it with a meter, but not good enough to actually do anything. Clean that up and make sure you have power going to the injectors with the main relay engaged.
I had similar problems on my ETA. For weeks. Tested relays, ignition, fuel pump... turned out to be very similar to this. Negative terminal on battery was not tight... felt pretty stupid when I found out :laugh:
nautilus
Posts: 35
Joined: Oct 05, 2021 10:30 PM
Location: Champagne-IL

Re: No start issue

Post by nautilus »

Thanks for the initial replies - after doing some more digging, I've realized I must have had one too many beers or a major brain fart when doing my initial diagnosis... corrections follow!

- with the main relay in place and ignition on, the 87 pins are getting power; double checked this by testing the cables under the plug
- the fuel injectors are also getting power, assuming the correct way to test is by using a ground on the body and not the second pin in the plug :roll:

So we have power to main and fuel relays and the fuel injectors but no spark at the plugs.

Both crank and flywheel sensors test good according to Bentley specs - 950/960ohms on terminals 1&2 and infinite (unmeasurable even at 20M ohms setting) resistance on 1/3 or 2/3; they're also new this year, which I realize doesn't preclude them from failing.

Battery terminals are clean and tight - I gave them a really good clean earlier this year during the initial "my car doesn't start thread"

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1st 5er
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Re: No start issue

Post by 1st 5er »

nautilus wrote: Nov 27, 2022 6:39 PM

So we have power to main and fuel relays and the fuel injectors but no spark at the plugs.
Cap and/or rotor.
nautilus
Posts: 35
Joined: Oct 05, 2021 10:30 PM
Location: Champagne-IL

Re: No start issue

Post by nautilus »

1st 5er wrote: Nov 27, 2022 10:12 PM Cap and/or rotor.
Both are new this year with less than 2k miles, but will take a look, thanks
Mike W.
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Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: No start issue

Post by Mike W. »

Are the injectors firing? Pull a plug and take a look. Since you know the ignition isn't working, if the injectors aren't, it points to something telling, or rather not telling, the ECU the engine is turning. If the plugs are wet, it could be the big transistor in the ECU the solder joints on which are a known problem.
Fedaykin528e
Posts: 685
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Re: No start issue

Post by Fedaykin528e »

Might as well bypass the anti-theft system to eliminate that variable, it can cause this situation:

viewtopic.php?f=3&t=137797&start=25
nautilus
Posts: 35
Joined: Oct 05, 2021 10:30 PM
Location: Champagne-IL

Re: No start issue

Post by nautilus »

Hey all, slow to update because the garage has been too cold to work in...

I continue to dig into this and think I may have found the issue - although the resistance for the ignition coil was @ Bentley specs, checking the voltage on it between +ve and a ground with the ignition on = 0.83v - this seems way too low (I would have thought 12v?), but I can't find anything in the Bentley to confirm what it should be.

Does anybody know what it should be?

Fedaykin528e - bypassed the anti-theft earlier this year when I was getting it first up and running
1st 5er
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Joined: Jun 13, 2008 12:15 AM
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Re: No start issue

Post by 1st 5er »

A known good used coil should be fairly easy to come by, as they rarely fail.
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