CFI Misfires/drivability issues

[kishy]

My characteristic miss (at highway cruising speed as well as in gear on the brakes at a light) has happened 4 or 5 more times (individual instances of the jerk/buck) in the last couple days. Odd.

I now have yet another harness on my hands (whole engine harness for $5? OK!), and I'm thinking if I can get the garage cleaned up I'm going to totally dissect my original one and re-do the crimps and everything. "IF" I can get the garage cleaned up. And I'm still keeping in the back of my head that the aging components in the ECU could contribute as well.

New spare harness came out of a carb swapped (complete with aftermarket 4bbl intake) '85 Vic in Detroit. Had an aftermarket TV cable retrofit on the trans, and one of the emissions solenoids was spliced into with a wire going back somewhere near the fuel tank. Didn't investigate exactly where it went, just seemed like an odd thing to tap off of. Some sort of tailpipe igniter maybe?

[kishy]

Merry Christmas!

KOEO 11
CM 14 (PIP), 18 (IDM), 41 (lean)
KOER 41 (lean)

Deja vu!

Harness fun may have to come sooner than later. Oh well.

[DerekTheGreat]

Welp, there's your miss. I thought the yards were closed for the holidays? I would've went this past Saturday...

[kishy]

It was the 23rd I was over there. Buddy is in town visiting his family in Center Line so we made a social outing of it. May be back today as it happens, unclear if junkyards are going to be on the tour or not.

On the bright side (maybe), this harness and ECM swapping business has confirmed that everything at the ends of the harness works. It can be said with a pretty high degree of confidence that the problem exists in the wiring or the ECM components sliding out of spec with age. Doesn't necessarily make it easy to find the exact problem, but I know it's compartmentalized to that area, and that's helpful to an extent.

If I had a continuity tester that made noise (e.g. continuous beep sound) that'd really simplify checking for breaks in the harnesses, but I don't even know where to find one of those. Problem is the car doesn't seem to notice when I go vigorously shaking the harness so I have yet to have any success doing it that way.

[DerekTheGreat]

I've got a Fluke meter that does just that. Expensive little bastard...

[gadget73]

Even cheap ass digital meters have the screamer these days. Pretty sure even a Harbor Freight meter will give you that functionality.

[sly]

Even cheap ass digital meters have the screamer these days. Pretty sure even a Harbor Freight meter will give you that functionality.

*grabs HF special cheapo DMM*

Nope. No screamer on this one. You do have 200 OHM range you can use. My leads ring out 2 OHM. So anything between 2 and 3 ohm I would count shorted using that meter.

[gadget73]

Meh, always knew those were garbage. I won't own one, I work on things that run at hundreds of volts and the last thing I need is for some shit-ass meter to explode on me.

Either way, meters with screamers can be had for not exorbitant sums.

[sly]

I give them away when someone needs a DVM. They're free with those coupons... so it's not like I'm out anything... and if the person fries it... it's no big loss for them either.

[gadget73]

I'm less concerned about killing the meter than I am about killing me. For low voltage work its probably fine, I just don't trust them to not explode when wired into a mains power feed or one of the high voltage connections in a tube amp. I realize not everyone does that kind of thing on a regular basis, but I do.

[sly]

oh yeah... definitely only low voltage side stuff. And the people I give them to are generally doing automotive stuff trying to test sensors and check voltages point to point. Works great for that crap. Definitely don't want to be using it on anything over 48V (telephone line). But for generic car crap, no issues.

[kishy]

Well, since this thread basically chronicles my misfortunes, might as well share lol.

As it happens I do have a meter with a beeper, I just never realized the little speaker symbol beside the continuity mode (which I didn't realize it had, I just always go on the lowest Ohm mode usually).

Unfortunately I was not able to make any progress in figuring out what is defective with my (factory, not installed currently) harness. I specifically looked at the Signal Return (pin 46, black with white stripe) ground and that connection is reliable all the way through to all of its ends, regardless of bends and wiggles. The point where they all join together is a high pressure crimp and was encased in a ball of plastic that was melted in place around it. This looks to be how the joints are made in this system and as much as I wish it was at fault, it isn't. The wires are bright and shiny, with no evidence of corrosion.

I have somehow found myself with quite the collection of computers, 4 counting whichever is installed at any given time. Catch codes are SG (2), MN, and D3MN. The SG computers (both are E4/1984 units but one was in a 1985 wagon) run way, way worse than the MN/D3MN units do, installed in the same harness with all variables identical. As the MN/D3MN units are newer it stands to reason there is some increase or upgrade in tolerance to something which reflects in how the car runs when experiencing whatever my problem is.

There is one thing which I have not verified, or not very successfully, and it's the reliability of the main harness ground to battery negative. It is done by way of a single terminal pull-apart connector, which you can unplug to clear KAM without fully disconnecting the battery (kind of a nice touch).

The car is degrading back to the state it was prior to the 'new harness' and 'new computer' which rectified all the problems. It's not quite that bad yet, but it's getting there.

I believe my problem has to do with the fuel mix leaning out. The lean code is accurate. It will suffer power loss at weird opportunities where a slight kick of the throttle seems to wake it up. An extreme lean condition might be the cause of the jerking too. That being said, important not to forget that unplugging SPOUT will make it run like a dream...

When the jerk occurs, there is a visible change in the exhaust vapour (benefit of working in cold conditions) where it's almost like the car briefly did not push out any exhaust.

I put the brake on (vacuum release is capped off), chocked the wheels, left it running in gear and went shaking various regions of the harness, bending and tugging on them. Nothing really seems to change what it does specifically, but after a bunch of shaking it seemed to stop so I went for a drive, and it stayed OK for a while before it went back to crap again.

As it's now running poorly with all of my computers (to different extents based on catch code of specific computer) it's reasonable to say the computer is not at fault; the probability of all of them being bad is just too low. But how can I have a wiring break but not see changes from shaking the harness?

[kishy]

Swapped the harness for the third one. Issue exists identically. So that's same issue with 3 harnesses and 4 computers, yet all sensors in the system have proven to work correctly with one of those harnesses previously.

Found fuse link for charge cable pretty much obliterated (in its prior vehicle, as it had been wrapped up in tape to "repair" it). Replaced (temporarily) with a length of wire. No change. Worth a shot anyway.

Starting to think outside the box...ignition switch?

[gadget73]

Ignition switch is possible, they are a common problem area.

How's the harness within the CFI unit itself? Its short but if you lose connection between the injectors and the plug it'll go batty

Oxygen sensor good?

All connections between battery and fuel pump good, including all of the plugs and the relay?

Have you ever driven around with a fuel pressure gauge connected to the test port to make sure the pump wasn't slowly dying and losing pressure as it gets hot?

[kishy]

Ignition switch is either original or was Ford dealer replaced, as it still has the tamper proof screws. Original seems more likely. Will investigate.

Never verified the tiny little piece that goes from the injectors to the actual harness connector. Good point. Will poke around with that. It's an important length of wire, yet one I haven't touched yet.

O2 is good, original/new/second new one all do the same thing, so it's not that.

Pretty confident re: power delivery to fuel pump/relay. Unfortunate that the connector above the axle is not able to be back-probed, all I know is the pump gets full battery voltage, but I can't see what it looks like while connected and running.

The pump is new. Have not done much in the way of testing it other than verifying that it primes to good pressure and engine runs with good pressure, including in the instances where the problems occur.

The biggest problem for me really is that the symptom presents itself more or less the same, but everything that can possibly be checked seemingly has been, just not all at one time because I really don't have time to re-do the entire batch of poking and prodding everything every time the symptom resurfaces.

I feel like a mechanic would have the same problem and this would be one of those cars sitting outside the shop for 6 months going nowhere. I did buy it off a mechanic. Never again.