5ktq electrical issues update...

[Bernard Littau]

Hi Cody,

Some comments in-line...

> Last night I decided to double check what my dad was seeing with the
> timing. I dunno what he saw, but I noticed 2 things.
>
> 1)It didn't retard like he said it did.
> 2)You can clearly see with the timing light at night sporatic missfires.
> Even just with the car idleing and no extra electical stuff on and the
> engine not audibly missing you can see that about 1 out of every 5 or 6
> times the plug doesn't fire.

I've had inductive timing lights give me indications of sporadic misfires
even when there were no actual misfires.  I'd say your test and test
equipment are suspect until you can prove to yourself what you are seeing is
really misfires.

>
>
> So last night I had an EE friend over helping me.

EE friends are nice to have.  Maybe he has access to an oscilloscope?

> We went through testing
> all of the grounds, everything good. Checked all of the Mac-11 feeds and
> grounds too. Then powered the EFI off the battery with a test lead (no
> time to do relay yet), which didnt help. Then we powered the injectors
> directly off the battery and the car seemed to be fixed. During all of
> this it was charging to 13.8v and dropping only down to 13.3 at the lowest
> with A/C and lights w/ highbeams. With the injectors not off of the
> ignition switch the car wouldn't miss at all, so I wired in a relay and
> put everythong back together (door panels were off for window issues, most
> of the dash was out for testing stuff) and went for a 5 minute cruise
> arround the shop. All was good so I decided to take a longer ride, so I
> called a friend and put him on resue alert in case it died on the road,
> then went driving for an hour. I got stuck by 2 trains near a station
> doing 5mph and was idleing for a good 20min of that hou!
>  r. About 45 minutes in I started noticeing the car was missing
> momentarily as the rad fan turned on, but then it would be ok once it was
> running. I looked over at the computer and the voltage was back down to
> ~13.3v cruising, 12.9 when the fan turned on. 5 minutes later (I had
> turned arround at this point) it got to the point where when the fan
> turned on I had to turn out the lights to keep the engine running, and
> voltage was going to 12.3v when the fan came on. I did end up making it
> home, albeit barely.

We need Scotty, I think.  He could always get the stuff fixed the first time
and then have it work, battle tested.  I can never seem to do that.

>
>
> I'm confused. Seems theres 2 problems, 1 with intermittent charging, and
> another with something not getting enough voltage when the battery is at
> or below 12.8 causing the miss. Seems when it charges right it charges
> enough to mask the missfire issue by keeping the voltage up above that
> 12.8v mark.

Good point about there being two problems.  The obvious one is the charging
system.  At this point, I think you need to concentrate on that one.  Having
your system voltage at 12.3 means you likely have a fully charged, topped up
and happy battery running the system with negligible or no alternator input.
Clearly, this is a problem, and it's quite tangible.

The misfire problem is likely related to the charging problem.  It may not
be as directly related as simple voltage.  This is a nasty intangible
problem.

Here is a possibility:  Your alternator is putting out some AC, and that AC
is disrupting your ECU.  A bad diode in the alternator can cause this kind
of problem.  Hook up your volt meter and measure AC.  It should read 0.0
volts.  Check AC when your DC reading is 12.3 volts.  Maybe you are getting
1-2 volts of AC superimposed on your DC (voltage rapidly fluctuates between
10 and 14 volts -- the DC meter would read 12 volts)

An oscilloscope would be a valuable tool here.  I picked one up for 100-200
dollars used a few years ago.

I have one of these:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2562211299&category=45005

Here are a bunch more on ebay:
http://listings.ebay.com/aw/plistings/list/category45005/?from=R4

If you buy any oscilloscope, make sure it comes with some good probes.

You can use the oscilloscope on the input to the coil to see if there are
really times when the coil is not being fired by the ECU.  It is also
possible to hook up an oscilloscope to the high voltage side, even right at
a spark plug, but you need some kind of shunt to keep from zapping your
oscilloscope with the high voltage -- good project for your EE friend to
help you with.

Best,

Bernard Littau
Woodinville, WA