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  Will an '86 2.5L 5spd ECM work in an '84 SE 4 spd?

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Will an '86 2.5L 5spd ECM work in an '84 SE 4 spd? by David Hambleton
Started on: 04-09-2015 06:42 AM
Replies: 11 (237 views)
Last post by: Lou and Blue on 04-21-2015 01:32 PM
David Hambleton
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Report this Post04-09-2015 06:42 AM Click Here to See the Profile for David HambletonClick Here to Email David HambletonSend a Private Message to David HambletonEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have an ECM from an '86 2.5L 5 spd. Would it work in an '84 SE 4 spd?
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Gall757
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Report this Post04-09-2015 09:24 AM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
They are different numbers.....but sometimes that does not matter.

86 5 speed = 1226864

84 4 speed = 1226156

the PROMs are different also.
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David Hambleton
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Report this Post04-09-2015 09:54 AM Click Here to See the Profile for David HambletonClick Here to Email David HambletonSend a Private Message to David HambletonEdit/Delete MessageReply w/QuoteDirect Link to This Post
I saw the numbers were different in the GM '84 to '88 Fiero parts catalogue. The catalogue sometimes shows pictures of parts that don't match the actual parts. I don't know how accurate it is...
I could swap the PROM...

[This message has been edited by David Hambleton (edited 04-09-2015).]

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Chelo Fiero
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Report this Post04-09-2015 10:25 AM Click Here to See the Profile for Chelo FieroClick Here to visit Chelo Fiero's HomePageClick Here to Email Chelo FieroSend a Private Message to Chelo FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have an 87 5sp with the 86 4 sp with no issues!
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fierosound
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Report this Post04-09-2015 10:58 AM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageClick Here to Email fierosoundSend a Private Message to fierosoundEdit/Delete MessageReply w/QuoteDirect Link to This Post
The 84 ECM is has "card edge" connectors for the harness - only year I think.
Not sure if the 86 has pin type connectors - someone with 86 Duke will have to confirm.

Top ECM in pic is from 84, bottom is an 87 V6 ECM.

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theogre
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Report this Post04-09-2015 11:19 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
84-86 engine will work but:
use 84 engine harness. C500 is different.
use 84 dist and coil or splice in new ICM and coil. Second option maybe easier to find ignition parts.
gm change throttle cable and TBI connection. Use 84 TBI or find correct cable.
5 speed need shifter cables, maybe shifter.

84-86 ECM different # but does matter. Prom have some minor changes but will work.

w/o headaches, 87-88 DIS engine is allot different wiring and can't use 84 engine wiring harness w/o issues because 84 is only made to use "old type" l4.
switch dis motor is easier for 85-86. Later years are made for use w/ different power trains as plug and play items for C500 and C203.

also See my Cave, Duke Quick Ref

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[This message has been edited by theogre (edited 04-09-2015).]

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theogre
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Report this Post04-09-2015 11:37 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fierosound:
The 84 ECM is has "card edge" connectors for the harness - only year I think.
Not sure if the 86 has pin type connectors - someone with 86 Duke will have to confirm.

all l4 use edge type.

87-88 l4 has different pin out and more "pins" because added MAT.
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David Hambleton
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Report this Post04-11-2015 05:09 PM Click Here to See the Profile for David HambletonClick Here to Email David HambletonSend a Private Message to David HambletonEdit/Delete MessageReply w/QuoteDirect Link to This Post
A couple of years ago, I replaced the rattling 2.5L in my '86 with a 2.5L from an '87.
Today, I replaced the 31 year old 367,600 kilometer ECM in my '84 SE 4 speed with the surplus ECM from the '86.
The hope was it would solve the issued discussed here: http://www.fiero.nl/forum/Forum2/HTML/135078.html
The engine started right up and seems to be running normally.
As I suspected, the shift light comes on to suggest 5th gear, but since I don't have one, I tilt the wheel so I can't see the light.
The light goes off over 3,000 RPM; about 100 kilometers per hour or 62 mph.
I presume if I swapped the PROMs, that issue would disappear.

Thanks for posting, guys. I appreciate it.
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David Hambleton
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Report this Post04-20-2015 10:34 PM Click Here to See the Profile for David HambletonClick Here to Email David HambletonSend a Private Message to David HambletonEdit/Delete MessageReply w/QuoteDirect Link to This Post
The engine has been running fine with the '86 ECM, just the shift light looking for 5th gear when there isn't one.

So, I swapped the '84 prom in to match the 4 speed trans and the idle went to 2500rpm with a continuous check engine light.
Went for a 4 km test drive; check engine light stayed on and idle at 2500 rpm.

Swapped the '86 PROM back in and am back to normal, (except for the shift light). Hmmm...

Before the cracked block engine was replaced in '87 under warranty, the idle was 900 rpm. Thereafter, mostly 1400 rpm. It would only drop to 900 rpm when it was raining. With the '86 ECM, it idles consistently at 900 rpm. Another hmmm...
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phonedawgz
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Report this Post04-21-2015 07:40 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
Put a piece of tape over the light.
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David Hambleton
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Report this Post04-21-2015 09:37 AM Click Here to See the Profile for David HambletonClick Here to Email David HambletonSend a Private Message to David HambletonEdit/Delete MessageReply w/QuoteDirect Link to This Post
I don't usually resort to such highly technical solutions. The tilt wheel obscures the light; I still know it's on. The same issue would exist with the tape. And I'd have that non-stock tape there. Can't do it.
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Lou and Blue
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Report this Post04-21-2015 01:32 PM Click Here to See the Profile for Lou and BlueClick Here to Email Lou and BlueSend a Private Message to Lou and BlueEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have a 1985 v6 4spd ECM for sale if you (or anyone) are interested. I had it all boxed up to sell but another member who was going to buy it dropped the ball and disappeared off the planet and never sent payment. And now he won return any emails or PMs and its been two weeks. I also have a black one that I think may be from an 88.

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