Added another Fox to the fleet - 1985 Marquis LTS

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Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #75 – December 29, 2025, 08:05:07 AM

So, I dug into it a bit last night.

The program was commanding for fuel pump activation, but the ECU was not sending the signal. I discovered this while running the ECU with the Stimulator on the bench.

I've run into this before on these, so I hunted down the transistor for the fuel circuit. You can see the old one on the bench and the new one (next to the MAP sensor hose) ready for soldering.

Hooked things back up to the laptop and now we have FP signal (The LED on the lower right)

The weather is pretty gross today, but I may brave it for a few to plug this all back in and see if we can get signs of life out of it.

Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #76 – December 29, 2025, 04:21:23 PM

Well, I made an attempt earlier to start this thing, and while I have fuel pump function, it seems like the injectors aren't firing. Things check out with the Stimulator, and the adapter board is just a passthrough.

I need to trace forward to see if it's something in the harness, or what. Too cold and windy today to mess with it.

Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #77 – December 30, 2025, 10:49:09 AM

Wind is pretty crazy here too.

Hope it is a simple find and fix.

Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #78 – December 30, 2025, 10:53:07 AM

You have the patience of a saint, Chuck. Most of us would have no idea how to work through a complicated electronic issue like this. Kudos to ya.

Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #79 – January 01, 2026, 05:06:46 PM

OK. I had to finish up a house project by yesterday (Solar battery), but I decided to brave the chilly temps this afternoon to do some trouble-shooting.

I rigged up a couple test lights and set about to verify spark and fuel.
I had spark and the injectors were firing. I pulled a plug to check to check to see if it was wet, and it had some fuel on it.

I decided to recheck the timing. I rotated the engine to my 10* BTDC mark and popped the dist cap. Sure enough, I's somehow managed to get the timing 180* out. I pulled the dist up and rotated the rotor 180* and put things back into place.

Then it started to make the proper noises. I got it running, but couldn't get it to idle and I know I need to work on the tune.

By this time I was starting to get a bit chilly, and the laptop ran out of charge, so I took that as a sign to stop for the day.

Not a 100% success, but I know that my ECU and the adapter are good. Just need to fiddle with the tune now.

I still have to secure the fuel lines down, but the clamps I needed didn't show up until yesterday, so I'll get to those soon enough.

Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #80 – January 03, 2026, 07:21:10 PM

So this happened today.

Running!

We had some family visiting through this morning, so I only had a couple hours yesterday to try and get the fuel lines secured. That failed, so I left things alone, as I knew I was going to try and start it today.

After setting the base timing and flashing a revised tune that I liked a little better. The car fired right up and began to idle. I'm not running an idle control valve, so I adjusted the throttle slightly. Idles at about 700-800 rpm. It was 30*F outside, and it didn't miss a beat.

Had to chase the cooling system around to get it to fill up. Once I was satisfied with that, I put it back on the ground to shuffle cars around. (I needed to move the TBird and the Beetle around to get this out of its work spot).

Once I got the trans filled enough to get it to move, I took it around the block to put some more gas in it. I need to add a little more ATF, evidently, but other than that it seemed to shift OK.

My WBO2 stopped reading correctly during all of this, so it was pegged full rich, but the sensor shows it's "at temperature" and was working for the initial start up.
Gotta check that out, but it is for sure not running rich. Throttle response is good, and it revs clean when I blip the throttle.

At some point I lost my tach signal when converting things. I cut out a couple things, including the diagnostic plugs, so I need to trace that down.
My HI-speed fan output isn't functioning in the car, but it was on the stimulator. I'm not seeing the indicator activate in TunerStudio, so another mystery.

Waiting on more materials to do the fuel lines now. I couldn't get the nylon to cooperate well enough to my liking around the frame rail, so I'm working up a solution.

Good to finally have it running again, even if I have a couple things to button up.

Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #81 – January 04, 2026, 03:58:29 PM

Fired things up again today after a tweak in TunerStudio and I have proper WBO2 readings again. I messed with the warmup routine a bit while it was coming up to temp.

Still don't have a working HI speed fan, and it might be a problem in the MegaSquirt itself. More digging on that to come. Might just switch which output I'm using.

I still can't figure out what happened to the tach signal.

The tach signal comes from the coil, but at some point in the process of cutting out the excess in the wiring harness, I must've removed something needed. The only thing that is even close is the old diagnostic plug. I cut it out at the splice and redid the splice with the wires that remained. I'm tempted just to run a new lead to the cluster. The LTS (and the LTD LX and Police versions) were the only ones with the tach, and none of the wiring diagrams have all of the info.

Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #82 – January 05, 2026, 10:58:45 PM

OK. Mystery solved on why the outputs (temp related) weren't working.

I originally wanted to use the Ford sensors, as I had a good set of them. MegaSquirt is base coded around GM sensors. The resistances are different.
Now, you can change the settings to use other sensors, but it's much more difficult with the old, MS1 stuff. I got the settings for the gauges to change without problem, but I couldn't get the firmware changes needed to work properly.

So, what I had happening was, while I had good readings on the gauges in the TunerStudio dashboard, what actually runs things is the firmware. The gauge might be showing 205*, but the ECU wasn't seeing that, and thus wasn't switching the output channel.

My TPS related output for the WOT signal to cut off the AC compressor was working fine, as it hadn't been altered.

I should have parts for this and the fuel lines this week, so hopefully I can get this fully on the road next week.

Re: Added another Fox to the fleet - 1985 Marquis LTS

Reply #83 – January 10, 2026, 04:06:05 PM

Got some time today before the rain came in to get the fuel lines and the fender liner wrapped up.

I was limited to 12" lengths of hardline that had the proper quick disconnect ends on both ends. Until I source a new or used set of factory metal lines these will work just fine.

Got a little kink in the feed line, but my hand bender is kinda cheap. Not going to affect anything though. I cut down the nylon line as needed and fit new straight female quick connect ends to them to mate to the hardlines. The hardlines fit the fittings I was using in the engine bay, so no changes were needed there.

Fitting the fender liner took more work than it should've. I had to relocate the HVAC vacuum reservoir and then had to straighten the fender a bit on the rear of the wheel opening to get the liner happy and fit up properly. This is the damaged fender, so it wasn't too unexpected.

With that wrapped up, the car is road-worthy again. Ready to put miles on it to sort the tune. Once I'm happy enough, I'll switch it to a NB O2 sensor.

A couple things to deal with in the near future.

- Sort the location/mounting of the MS ECU. I'll probably need to extend the harness for this for me to be happy, but it won't affect things in the short term
- Get the tach working again. (Still a mystery)
- Mount the fender-mounted wiper/washer tank-pump. The old engine bay one was displaced by the battery.
- I've been needing to figure out what's binding on the DS door lock I replaced the switch a while back, but it won't stay down and stay locked. Gotta pull the door panel to sort that out.
- Clean up/loom wiring in the engine bay.

Glad to have it drivable again