1998 SVT - Won't Run

[ZeroHour]

So ran into some interesting issues today...

About 2 weeks ago my temp gauge sensor went. I parked the car until I could fix it. No other issues at the time. Checked the sensor (driver side block, below TB, Sensor had seen better days and rubber/plastic grommet inside the brass had degraded.

Ordered replacement, went and installed this morning. No big deal. Turn the key, Gauge dropped from the top end and back down to the cold end.

Buttoned everything up inside the engine bay. Went to start the car. Terrible idle. stays running, but has a "hiccup" which can be heard from the pod filter. Hiccup is followed by a burple in the exhaust (sounds like a misfire).

I'm thinking this was just the car sorting out the IAC because the battery was disconnected and let it run. But the issue continued even after the idle has settled.

Shut the car off, started it up, brought it back in the garage.

Did the general checks, all the stuff I touched. Listened to fuel pump, all good. Listened to motor, sounded fine. Just the burple during the "hiccup".

"Hiccup" got a bit worse. Shut the car off, and restarted again. Now it won't run. I suspected the IAC. Jumpy Tach while attempting to run.

Disconnected the IAC, Got the engine to run without the IAC, stayed running without the "hiccup".

Went home, I had a spare IAC which was replaced on another car, and I had a spare gasket with that IAC. Really went to get the gasket, local stores had none in stock...

Pull the IAC and cleaned it. It was a little dirty, but I've seen worse. Re-assembled with cleaned IAC. Started the car, no tach. Engine won't run.

I don't have my sensor scanner, so start looking over my work again, assuming I've missed a hose, took off a ground, etc. No dice.

I've started looking over the harness. I've noticed a few cracks. One bad, exposed portion of wire, everything else minor. I did some quick patches with liquid electrical tape. Car still does not run. Tach comes back.

Pulled the wire connect off the new temp gauge sensor, which is what I was repairing. No change. Gauge didn't work again, but the car still would not run. Put the temp gauge wire back on.

Went home, got my sensor reader. Went back to the garage. Reader shows the IAT to be -40F. So assuming bad IAT, and maybe that is causing all the bad idle issues.

Went home, got a spare IAT sensor from a non-SVT. More or less the same sensor. Went back to garage. Same issue, no read on the sensor.

I took more loom apart. I don't see any further issues. Wiring inside the plastic loom is fine for bot the IAT and the MAF going into the larger portion of the harness.

Begin to check the other half harness, passenger side, never rear valve cover.. Not much else to touch there, just added spots of liquid electrical tape. I had not touched this area previously, but I know the engine temp runs through that portion of the harness. Assuming the IAT does as well (wire color matches).

Being adventurous, and not going home again for a voltmeter, I put a jumper in the IAT connector. Sensor Reader shows 302F. So the cracked wiring is sender/receiving some sort of signal, or at least can read the analogue. Not sure of the signal type.

Put it all back together another. Had to charge the battery a few times today from all the starting/powered-not-running testing. Car is still a hot mess, but I'm out of ideas. Anyone have suggestions? Am I at the point of pulling the entire engine loom? Only thought I had was the rear harness incurred new cracks when I pulled the IAC. But after 11 hours in the garage, I'm done for the day. Any help would be appreciated!

 

[ZeroHour]

Follow up on this original post.

I was able to get a replacement pig tail for the air intake temp (IAT) sensor. This came from a newer Cougar with much better wiring. When I clipped my original IAT wire, the copper downstream from the actual break was also green (corroded). The new pigtail was crimped and shrink tubed back into place.

Testing showed my IAT now functions normally. Maintains reasonably close to ambient at start up and slowly rises during operation.

Second problem. Car ran and started a few times and with the air temp now working I went for a drive. All went well until 10 minutes in when the electric fans kicked on.

Whole fans are running, I'm back to getting the 5 second hiccup. Car was parked while this happened but I left it running. Once fans kicked off, the idle went back to normal (no hiccup). I still suspect this is the idle air control (IAC) causing the hiccup. Car threw no codes during this run.

I looked over the fan harness today, looks okay. Noticed a small chaffing mark on the ground going from the passenger side fan to the front chassis/upper radiator area. Unclear if this ground was making contact or has been this way for some time. Touched up this mark and cleaned up the ground location, although the bolt was clean for a 15 years old and I've seen worse work as a ground. So no suspect of the ground wire.

I also touched up a bit more of the passenger side wire harness at the connectors by the rear valve cover. I'm hoping there is some resolution for my efforts. I've looked over the visible harnass. If this doesn't work, I'm guessing I'll need a full E0 harness.

Does anyone have any ideas on how the idle air control and fans would be interrelated? Is there a point where the fan wires or fan trigger wire are in the same loom as the IAC wire?

 

[ZeroHour]

Additional updates today:

Car will run and idle fine until fans engage. Relay is tripping around 202F. Fans run until temp is below 196. This seems to be normal. Driving temps seem to be 185-190F. No suspected issue in the cooling system.

While fans run, idle begins to hiccup.

Fan relays pulled, no change, except fans shut off.

Pulling fuse R4 while fans are operating stop hiccup. Fans stay running as R4 is for AC clutch relay.

Based on troubleshooting, if fans are active and running ac (on ac or max ac), idle stops hiccups.

With R4 Fuse is installed, AC turns on and did blow cool air.

Checked AC clutch, it does not appear that the AC clutch is trying to engage while hiccups are happening. This rules out the hiccups being caused by the ac clutch trying to repeatedly engage.

I'm going to try and source a spare AC Clutch relay and see if this stops the issue.

Have not seen any strange behavior from the tachomete, speedometer or other gauges. I suspect the issue is linked to the relay or fuse box itself.

 

[satya_svt98]

Really sounds like a wiring issue.. I"m still not sure what you mean by "hiccup" tho.
Where are you located? I might know a contour owner in your area..

 

[BrApple]

If you are getting a rhythmic change in idle with the AC turned on, chances are the system is low on R-134a. This will cause the idle to fluctuate as the compressor kicks on and off.

 

[ZeroHour]

Received notices for this post in the VB inbox....not sure why. But to close this out, it was ultimately the wiring harness that was shorting due to the notorious poor longevity of the OEM wiring. The harness was pulled and all visibly bad wires replaced. Car has been running fine since the harness was fixed.