IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

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Ed Lijewski
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by Ed Lijewski » Tue Sep 25, 2018 12:44 pm

After three weeks of daily driving haven't had any sudden/high idle episodes. Idle currently is good in all situations.

The change of TPS unit made the difference.

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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by my8950 » Tue Dec 04, 2018 12:57 pm

Interesting read....

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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by dimswits » Tue Dec 04, 2018 4:46 pm

Some years ago I inadvertently stumbled on the root cause of this while datalogging my turbo scorpio. I didn't have a bad TPS, rather, it was faulty wiring power distribution wiring, but the symptoms are exactly the same: The car drives fine for a while, then as if by magic, when coming to a stop during the drive, the idle revs up to 1500 rpm or so, and stays there. Cycling the car off and on fixes the issue for a short time, but it always returns.

The EEC-IV registers closed throttle as the lowest voltage reported by the TPS that is also greater than 0.49 V. Part throttle is a variable value that is 0.04 V higher than the closed throttle value. The closed throttle value is a continuous ratchet, meaning it's always the lowest value seen by the EEC for the current driving session.

What I was seeing in the datalog is my TPS would be at .85v closed. I'd drive and warm up the car. On decelerating to a stop the engine RPM would dip momentarily, causing an overall voltage drop in the whole car, and the TPS would correspondingly report just over 0.55v. Just for an instant. That 0.55v becomes the new closed throttle, and the normal closed TPS setting of 0.85 is 6 times the difference needed to trigger part throttle. Since the closed throttle voltage cannot increase, the car can never drop from part throttle mode down to closed throttle, and so the timing stays advanced and the IAC stays open.
Dimitri in NYC
88 Scorpio 2.5 Turbo
89 Scorpio 4.6 DOHC
02 E46 330Ci
17 MKC

Ed Lijewski
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by Ed Lijewski » Tue Dec 04, 2018 6:17 pm

That seems to suggest an EEC failure of dashpot mode, which shouldn't occur, but randomly does. But why?

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Bob Weir
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by Bob Weir » Fri Dec 07, 2018 1:53 am

Hi Ed

You already have Dimitri, but maybe you can contact Ken Kizer [http://www.aphenos.net/scorpio.htm] and Darren Needham for help. I have phone & email if needed.

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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by my8950 » Fri Dec 07, 2018 9:37 am

Bob Weir wrote:
Fri Dec 07, 2018 1:53 am
Hi Ed

You already have Dimitri, but maybe you can contact Ken Kizer [http://www.aphenos.net/scorpio.htm] and Darren Needham for help. I have phone & email if needed.
The is 404'd....

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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by DPDISXR4Ti » Sun Mar 24, 2019 12:34 pm

dimswits wrote:
Tue Dec 04, 2018 4:46 pm
Some years ago I inadvertently stumbled on the root cause of this while datalogging my turbo scorpio. I didn't have a bad TPS, rather, it was faulty wiring power distribution wiring, but the symptoms are exactly the same: The car drives fine for a while, then as if by magic, when coming to a stop during the drive, the idle revs up to 1500 rpm or so, and stays there. Cycling the car off and on fixes the issue for a short time, but it always returns.

The EEC-IV registers closed throttle as the lowest voltage reported by the TPS that is also greater than 0.49 V. Part throttle is a variable value that is 0.04 V higher than the closed throttle value. The closed throttle value is a continuous ratchet, meaning it's always the lowest value seen by the EEC for the current driving session.

What I was seeing in the datalog is my TPS would be at .85v closed. I'd drive and warm up the car. On decelerating to a stop the engine RPM would dip momentarily, causing an overall voltage drop in the whole car, and the TPS would correspondingly report just over 0.55v. Just for an instant. That 0.55v becomes the new closed throttle, and the normal closed TPS setting of 0.85 is 6 times the difference needed to trigger part throttle. Since the closed throttle voltage cannot increase, the car can never drop from part throttle mode down to closed throttle, and so the timing stays advanced and the IAC stays open.
I guess I missed this ^^^ when first posted. I've now read it four times and it's the most in-depth description I've read of this problem. Were you able to fix it D'?
Brad

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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by Bob Weir » Mon Mar 25, 2019 10:51 pm

I’m reading this post about Sudden Random High Idle aka “SrHi” = New Acronym for a Scorpio PIA!
Obviously, you guys all know so much more than me, but this is my story and I’m sticking to it.

Memories of a similar situation I had with my 88 Burgundy Scorpio.

It was the engine harness, specifically that 1/3 portion that lays on top of the engine and connects almost every engine management sensor and the fuel injectors. The other 2/3 connects to it and goes through the firewall to the EEC.

What really caught my attention was a post by dimswits of a decrease of voltage of TPS from .85 to .55v when decelerating in his Turbo Scorpio. Regardless, if he turbo’d a Scorpio v6 or swapped in a XR L4 is not important. What is important, are the similar if not identical sensors and the numerical volt variance from spec.

I referenced my Scorpio Workshop Manual. In the back is the EEC-IV Quick/Pinpoint Tests. In “short” [pun intended] the most prevalent volts are <4 or >6.

When I was diagnosing my 88 Scorpio, I rarely saw any numbers close to <4 or >6, let alone .85! My readings were ridiculous. So much so, I bought a new es380 multimeter. Same absurd numbers. I also bought Dan Sullivan’s book with the meter. His primary principle is “it’s the wiring preventing correct voltage flow, not the sensor”.

I also remembered installing Ford’s “improved” TPS connector with GOLD contacts including quality hot melt connectors. Apparently Ford was concerned with voltage when they upgraded the TPS connector.

Enough testing, I cut open the engine FI / Sensors Harness. Obvious! Missing insulation, strands of wire! I’m amazed the Scorpio even started. No wonder voltage readings were absurd.

Why random? Sitting idleing in the driveway with minimal engine shake, drive it down the street hit a few bumps and the harness moved = SHORT causing base idle shift = high idle. Shut engine off, computer resets at restart = runs fine - mostly.

Why only some Merkurs? I suspect different wiring insulation. Maybe the wiring was disturbed enough to break the insulation apart causing a short? We drove our 89 Silver Scorpio for 5 years, interstates to & through Philadelphia and it never misbehaved! Herson drove it to Chicago!

Related story. I had a 94 Benz Wagon, ran great for >33k miles until it starting going into “limp home mode”. In ’86, Benz starting having their WIRING HARNESS made with a new insulation. It took 10+ years until the insulation deteriorated! Much the same as in my Scorpio. Luckily it’s harness $1,000 had been replaced, but unluckily, not the throttle body $455 to rewire internals! The Benzes reacted the same way as our Scorpios; runs great, hitting the smallest bump disturbs the harness; the Benz goes into limp home mode, the Scorpio goes to hi idle. Computer resets at Restart - runs fine - for how long?

Suggestion: Open up the wiring harness and EEC! If I’m wrong, I owe you some electrical tape and plastic wrap. Note: If you buy another harness, pay attention to the connector to the harness portion that goes through the firewall. There are two different types of connectors. Maybe the connectors are the tell tale difference for why only some Merkurs? And you might as well open the EEC. My wiring was so bad, it toasted the EEC circuit board.

Bob
PS Thanks to all of you for helping me keep my Merkurs driving down the road and not sitting in the driveway.

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andyofcolumbusmerkur
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by andyofcolumbusmerkur » Tue Mar 26, 2019 8:23 am

Ya good stuff. Also think about how impedance (resistance) changes with temperature. And "all of a sudden for no reason" car starts acting up.
You can barbecue it, boil it, broil it, bake it, saute it. There's shrimp kabobs, shrimp creole, shrimp gumbo, pan fried, deep fried, stir fried, pineapple shrimp, lemon shrimp, coconut shrimp, pepper shrimp, shrimp soup, shrimp stew, shrimp salad, shrimp in potatoes, shrimp burger, shrimp sandwich....

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DPDISXR4Ti
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Re: IAC Issues, Scorp and XR, Maybe the "EEC-IV CHIEF" Knows How To Resolve?

Post by DPDISXR4Ti » Tue Mar 26, 2019 3:50 pm

A small data-point I'll add... I had this issue on my 2.3 when I was using a stock 2.3T (PF3 or LA3) PCM, but when I changed to a later, early 90's Mustang PCM (D1L1), the problem disappeared and never returned. Perhaps the factory calibration took into account this potential common problem and figured out a means to better handle it?
Brad

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