intermittant non-start issue is driving me nuts

[DRACO A5OG]

Oh no, please measure before you charge it up so we can see the current state of the battery.

When I was chasing down a no start low battery issue after swapping everything on the damn charging system, it turned out the positive side battery connector had a hairline fracture that was not allowing an adequate charging of my brand new battery from my brand newly re-built alternator.

When warmed up of course she started but if I let her sit she would either slow crank or not at all. Measured battery it was low, I was like WTF I was ready to yell at the FLAPS but went there and they tested my battery was Perfect, a little drained but it held its charge and CCA tested fine too.

I then decided I will replace both cables, neg side was ratty but when I removed the posi side, I noticed the fracture under neath, BINGO, replaced connector, not the cable, absolutely no more issues with charging system. I just hate for you to drive yourself nuts trying to locate the culprit.

[andyt11]

For what it's worth the battery has 12.3v right now and the car starts and runs. I'm going to top it up. Going through earth's over next few days and making sure they are all good.

[McLaren-TAG]

Intermittent stuff is difficult especially when they work 99% of the time. A faulty DME relay is a likely cause troubleshoot that, lots of details here with the two clicks being required but it's an easy check and you should already have a spare DME relay.

One thing I'll throw in and it's something that's a pretty straight forward DIY project. The DME itself, I have already had my car long enough to have replaced the CHT sensor, both speed reference sensors and the DME relay, a couple of months ago I took the car out for a drive Saturday night after having prepped it for an AX event on Sunday.

Sunday morning comes and no start, I did what I could at the time with very little time to troubleshoot, and it wasn't the DME relay. The car then didn't starts for a couple of days while I did my rounds of basic troubleshooting. Fuel checked, no spark so coil checked and everything was good.

I took out the DME, disassembled it and flowed every single pin on the connector and put it back... nothing was obvious but a very small cold solder may be extremely difficult to spot. I used to repair cell phones back in the late 80s and early 90s so I'm comfortable with electronics and a soldering iron. After the reflow everything worked flawlessly. These 3.2s are 30 years old plus, things happen. Don't be afraid to try the things that others have suggested here, often times they are golden. Its a good winter project even if it's not the case, it's always a prudent project to take on.

[DRACO A5OG]

Originally Posted by andyt11

For what it's worth the battery has 12.3v right now and the car starts and runs. I'm going to top it up. Going through earth's over next few days and making sure they are all good.

Well, per Bentley, 12.3 equals to approximately 62.5% of full capacity. I do not know about anyone else, but that is not acceptable.

What is the voltage when car is on at 1800-2000 RPMs, let's make sure alternator is charging her too.

[andyt11]

Thank-you for all the help so far everyone.

I've been through all the grounds tonight and removed and polished and reinstalled each and every one.

I have the battery off because one of the grounds was located behind the battery. While it's out I'll get it load tested. Just to make sure it's not at all questionable.

After that I'll check voltage at two grand and report back.

After that I'm thinking I'm going to reflow the DME board. I don't suspect the relay. I've got two and swapping them has never resulted in the car changing from non start to start, or vice versa.

Can you guys think of a way the coil could be the culprit or perhaps the ignition switch? I'm just thinking a few steps down the road here.i can't understand why it went from non starting to starting, just because I pushed it around the garage on Sunday

[andyt11]

Battery was fully charged last night. Currently sitting in garage with 12.6v.

Just leaving part source. He load tested it, says it's fine.

[DRACO A5OG]

Outstanding, now to the next suspect.

Alternator, please test at 1800-2000 RPMs and post voltage.

Side note, take a close look at the battery terminal connectors, above and below for any hairline fractures. Use a bright light and or magnifying glass. A fracture will cause havoc.

[andyt11]

Tested the battery at a second place on way home. They put it on two different machines and proclaimed a clean bill of health.

When I got home I hooked up the multimeter and fired up the car. Went up to 13.3 or there abouts at idle, but the engine died after about 3 seconds, never to restart. I will start checking coil etc tomorrow. Hopefully it stays broken.

[andyt11]

Just before I quit, I had my wife crank the car over while I watched for a spark. I don't have a spark.

[DRACO A5OG]

Oh man that sucks.

The OHMs on ref and speeds sensors check out too?

[DanielDudley]

These are exactly the symptoms I am having. Replaced the reference sensors and DME relay, and no change. I get tach bounce, and a big bounce when it decides to fire from dead when cranking. The old sensors appear fine, and are not really very old, old DME relay is fine.

Sure seems like a bad solder connection.

[andyt11]

I've got tach bounce too. Sensors checked out last year when I went through all this. Will check again but I'm sure they are going to be fine.

Could the coil or ignition switch be the culprit? If not, I think I'm going to have to open up the DME and attack it with a soldering iron. Seems like a big step to take.

[rick-l]

If you are nervous about that you could private message Ingo and see what he says about it.

I think he must be out of town or he would have picked up on this thread.

Pelican Parts Technical BBS - View Profile: ischmitz

[CCM911]

When mine went it was totally intermittent. Send the brain to Ingo for a test. Not expensive at all.

I went through the same thing as you. Changing the DME realys seemed to help, but was probably just coincidence.

Good luck!!

[ischmitz]

Just saw this and send Andy a message responding to his email. Now that there seems to be (some) spark I would introduce fuel just to see if that makes a difference. It somewhat points away from the FW sensors.

It could be an intermittent DME relay (fuel pump runs only sporadically), a bad fuel pump (weak output, happened to me), or something in the DME (spark output). Once you stray a healthy dose of brake cleaner or similar into the intake and then crank it'll tell you.

Cheers,
Ingo

[mysocal911]

Originally Posted by andyt11

Thank-you for all the help so far everyone.

After that I'm thinking I'm going to reflow the DME board. I don't suspect the relay. I've got two and swapping them has never resulted in the car changing from non start to start, or vice versa.

Most likely your problem is here:



That's the one of the three pins of the ignition driver transistor. Just re-solder each of
the three pins. You'll find the driver on the aluminum heat sink on the right side of the
ECM when viewed from the front. That's the most common problem with the ECM.

[DanielDudley]

Originally Posted by DRACO A5OG

Outstanding, now to the next suspect.

Alternator, please test at 1800-2000 RPMs and post voltage.

Side note, take a close look at the battery terminal connectors, above and below for any hairline fractures. Use a bright light and or magnifying glass. A fracture will cause havoc.

I went over the DME on my car, but it may in fact be a bad connection on one of the primary wires going to the positive terminal on the battery.

Definitely check the terminals on your battery. PO had messed with mine.

[andyt11]

Just an update. Ingo was kind enough to exchange some emails with me and felt there was a real chance my position sensors were failing or that the actual DME has a fault. I also checked in with Steve Wong since it's one of his chips in there. He had similar thoughts re the chance of a DME fault.

The insulation on the position sensors has failed completely from heat, leaving the metal shielding exposed to moisture. New ones have been ordered along with a new DME relay just for good measure. And the DME itself has gone to Steve for testing / repair. Ingo also offers this service and I'm sure either guy can take care of it. I only chose Steve because I've dealt with him before.

So thanks to all for the help so far. Especially Ingo for his detailed emails. I do appreciate it.

Will update when the DME comes back and the new sensors are installed. I'm hoping that's the end of it.

[DanielDudley]

Originally Posted by andyt11

Just an update. Ingo was kind enough to exchange some emails with me and felt there was a real chance my position sensors were failing or that the actual DME has a fault.

The insulation on the position sensors has failed completely from heat, .

Well there you go. Lots of threads on replacing these, but I found that I had to use a little WD40 and some vice grips to get out the worst offender. I also wound up putting a block of wood against the transaxle and using a pry bar against the vice grip to nudge it out. Removing the duct hose from the heat exchanger will give you access.

[mysocal911]

Since you have benefited from the Pelican Parts Forum and its info, you could have utilized Pelican Parts,
since it provides a rebuilding service too. Hopefully, you at least ordered your sensors from Pelican Parts, right?