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Old 04-25-2011, 12:03 PM   #1
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Question Engine stumbling, recent 1.8 swap into 1991

Hey guys,

I've come across a problem that is starting to drive me a little nuts mainly because I've spent so much time, effort, and money completing this 1993 Escort GT engine swap into my '91.

What's happening is the car is stumbling under abrupt throttle inputs off idle, and also stumbles under high load conditions in the lower RPM range (usually).

The car is throwing a code 9 for water thermistor open or short circuit, which seems odd as this is the same sensor I used on the previous engine and it has been carefully handled, etc. I will replace this with a known good tonight and report back.

Also, I am using the Flyin' Miata throttle body adapter plate to use my 1.6 TB on a 1.8 intake mani. I have the air inlet to the ISC plumbed into the intake, but the coolant lines are just capped right now. I hear many people have done this and it should only affect idle quality and not cause this stumbling.

The timing was set correctly and the engine runs great if you're easy on the throttle and in the upper rev range.

What do you guys think? Are there any other variables I should be looking into, ideas?

Thanks.
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Old 04-25-2011, 12:40 PM   #2
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Change the thermistor.
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Old 04-25-2011, 01:08 PM   #3
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or plug it back in.
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Old 04-25-2011, 01:21 PM   #4
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Attempted to re-seat the connector with no change last night. I'll replace the sensor but was wondering if there were any other reasons this may be occurring. I'll swap it and let you guys know once I'm back home tonight. Thanks!
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Old 04-25-2011, 07:26 PM   #5
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Hows the cap and rotor? whenever I had stumbling issues it was always ignition related.
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Old 04-25-2011, 07:31 PM   #6
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Quote:
Originally Posted by Bomdoutscort View Post
Hows the cap and rotor? whenever I had stumbling issues it was always ignition related.
Eureka. Must be the problem. No cap and no rotor. No wonder it runs badly.

Stumbling like you describe sounds lke a lean mixture. Fuel pressure up to snuff? Assuming OEM ECU?
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Old 04-25-2011, 09:13 PM   #7
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Quote:
Originally Posted by Bomdoutscort View Post
Hows the cap and rotor? whenever I had stumbling issues it was always ignition related.


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Old 04-25-2011, 09:16 PM   #8
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Quote:
Originally Posted by Bomdoutscort View Post
Hows the cap and rotor? whenever I had stumbling issues it was always ignition related.
0/10 unsuccessful troll
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Old 04-25-2011, 09:33 PM   #9
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Wow..


Miata's = coilpacks
FWD BP's = cap and rotor

Jussayin'
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Old 04-25-2011, 09:57 PM   #10
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Didn't understand that all miatas had coilpacks. When he said his engine was from the escort, I figured it was still using the distributor. Thats for the not so rude comment Shawn. Wow....
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Old 04-26-2011, 12:31 PM   #11
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lol, I love this thread already.

Anyways it ended up being a combination of the water thermistor and the coil pack grounding to the head. Just a heads up but if anyone completes this swap in the future the FM coil mounting bracket doesn't work for FWD engines or at least the 93 Ford Escort GT engine. It's possible to make the original 1.6 bracket work with some creative hacking with a hacksaw, sawzall, or plasma cutter (easy).

Seems to be running great now! Next on the list is a wideband and a Megasquirt.
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Old 04-26-2011, 12:33 PM   #12
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Part of the swap process is removing the original distributor and attaching the Miata CAS if you're using a FWD BP engine. Goes right in with no issues.
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Old 04-26-2011, 12:56 PM   #13
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Thanks for the clarification.
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