'85 Merkur XR4Ti Rally Car

In reply to Samebutdifferent :

The injectors are batch fired and have been confirmed to fire all at the same time.  I've rechecked the firing order a bunch of times, and even tried swapping the 2 and 3 leads to check if they were reversed.  I agree something looks screwy there, but everything I can test indicates that those two cylinders are firing.

I figured you had checked all the above multiple times over.  Having followed this thread for some time, you clearly know what you are doing and I have enjoyed the many posts.  Just like Nohome's issue with the Molovo, it's these kind of issues that makes us smarter.

"I have never had a car so actively resist living."

This has never been so true as now...

How long does it take for plugs to change color?  Thinking back, #1 and 4 may be slightly older since I initially thought the issue was only on those cylinders, and eventually replaced the other plugs as well.

EDIT:  Also worth noting that the two "clean" plugs didn't have any fuel on them when I pulled them, immediately after running up to operating temperature.  And the car hasn't been losing coolant, which is the other thing I'd expect to "steam clean" plugs.

¯\_(ツ)_/¯ said:

Compression test indicates things seem to be ok:

Plugs:

Next step is figuring out where I can dispose of the current tank of fuel.

I"m using the 6 gallons of decade-old fuel that came out of the e34 donor car for my lawn mower. It runs just fine on that old stuff........

¯\_(ツ)_/¯ said:

In reply to everyone who keeps saying v8 :

You guys do remember that I have already conducted this experiment once, right?

...that's not to say the data was conclusive enough to rule it out completely 

based on my memory of the controllability of that car, it would be meeting a tree about as fast as DeMasi at Sandblast last year.....

Really weird thought that might not apply to this engine...

Earlier this year my racecar was down on power and would hiccup at higher tpms.  It also idled at normal rpms, but kinda rough.

It ended up being the cam and crank sensors were plugged in to each other's spot in the harness.  No idea how it ran at all.  It only felt like 10 or 20% down on power....

If you have motortrend on demand, the Hot Rod garage guys just built a tbird turbo coupe. they went standalone(completely replaced engine harness) and LS coil on plug set up.

though it was like $1500 worth of standalone plus harness and coil set up.

Drained fuel:

It doesn't look or smell completely evil but still worth ruling out. 

I ran it a bit before draining.  Unplugging any one injector causes it to stumble worse so it's at least attempting to run on all cylinders.  The pump doesn't sound awesome but still made correct pressure at the rail, maybe it's worth throwing my spare in.  Fresh fuel after work today.

In reply to wvumtnbkr :

All sensors are plugged into the correct locations, but that sounds like something that could (at least sort of) happen on this if two or more wire splices are shorting to eachother.  I am going to unwrap the entire harness if fuel/pump are not the issue, then either repair (if I find issues) or replace the engine harness entirely.

10 gallons of fresh 93 and a bottle of Lucas' finest fuel unberkeleyener has had no effect whatsoever.  I think it's wiring time.

Are you going to go through the harness that’s in it?  

In reply to paranoid_android :

At least a little bit, but at some point it becomes more efficient to just swap the harness.

There are a lot more splices and kinks in these wires than I thought, hopefully one of these is the problem:

Ugh I hate hacked up wiring..... Goos luck. Use heat shrink crimp connectors for reassembly!

Is this thing super dependent on a coolant sensor the way e30's engine management is? If so, splices and whatnot could be berkeleying up the resistance curve.

bluej said:

Is this thing super dependent on a coolant sensor the way e30's engine management is? If so, splices and whatnot could be berkeleying up the resistance curve.

that's an interesting thought. The Porsche also is highly dependent on an intake air sensor and if its wiring gets too kinked/frayed (which happens all the time) the car runs like garbage.

Checked continuity of every wire back to the ECU connector- all good.  Every sensor's resistance at the ECU connector- also all good.  Every sensor itself.  Voltage at sensor plug.  Couldn't find anything and frustratingly chased a few non-issues for a while.

Finally, at around midnight, found a wire that would trigger the coil if I wiggled it, and one that would shut the fuel off if I wiggled it.  The pin/sockets for the ignition system ground wire (at the ECU) and the fuel pump (at the fuse block) are both loose.  Who knows how many other pins in that ECU connector are loose, so I guess my next move will be to attempt to swap the entire engine harness and make a new fuse block.

Can you de-pin the connector and tighten up the pin.  80s and 90s pins are usually pretty robust and can be tweaked.  Most of the newer micro pins dont have enough meat and have to be replaced.

Like this random Honda pin from my tool box.  If it was loose I could gently push the center in a bit.  Might be quicker an easier than swapping a harness to see if it changes the problem.

Well, if it makes you feel any better, I'm now in your same boat

I drove my SVO to work yesterday, ran great on the way there, but on the way back I started to get a hesitation under full throttle around 3k rpm and by the time I got home it was a misfire anytime I went WOT under load. I'm going to pull codes, but I am already suspecting a TFI and when looking for replacements, made me realize how almost all replacement TFI modules have terrible customer reviews. Are these that poorly made or just poorly designed?

In reply to olso3904 :

Personal opinion- yes.  The TFI (and distributor drive, and a number of other electrical bits) are garbage, and were even when new. That's why my car has two TFI modules so I can plug in another when the first inevitably dies.

If you do decide to pull/redo sockets and pins, I have a kit and the crimping tool to do them.  If the kit matches the size you need I can send you the stuff.

Good news on finding what really seems to be the cause of the issues. Gotta love old wiring. 

There are too many sketchy things in the old harness, swapping to the stock one from the parts car.  Old removed:

And now to make the new one match before installing:

I'm not convinced this will actually fix the problem, it may be that the bad connections were actually cooking components.  

That is a surprisingly basic harness. I think an e30 power window harness has more wires lol...

Even if you get the harness in and it makes no difference, it was worth while to get rid of all the splices and scotch locks in your other harness. Nothing worse than a harness with intermittent shorts or E36 M3ty grounds.

It's probably worth while to throw in a new set of plugs to use as witness marks, seems like these engines are really sensitive to plug type and gap