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Author
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Topic: ECM (ecu) swap help needed
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BG50rider
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Member # 5273
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posted
 
 
I bought my 1990 5 speed 5.0 LX a couple weeks ago. The car runs relatively well, but had a really hard time with cold starts and idled like it had a small cam. I checked the TPS and it was showing 5 volts at idle or KOEO. Swapped the TPS with a new one, same issue. WOT was decent, but not great. After talking with a friend, I found the orange EFI harness wire just wrapped up behind the block. Grounded it, and no change. Talked it over again and decided to swap out the ignition control module on the distributor. After that swap, the WOT driving was much smoother, but the idle is still pretty rough. I also checked the IAC and it works just fine. I cleaned it to be on the safe side. Also cleaned the MAF sensor. Last thing I thought about was the ECU. I picked one up from O'reilly that says it's for my year model and for a 5 speed. When I pulled the one out of the car, it had writing on the casing like it was removed at a salvage yard. On the outside, it said it was from an 88 5 speed. After swapping the new one in, the TPS can be adjusted as low as 1.01v (which is where I have it) and it started on the 3rd try (prior to the ECU swap, it would take at least 4-5 tries to start when cold). Once running, it seemed it was idling slightly smoother, but now has a check engine light. I'm hoping to get a code reader from a friend tomorrow. At any rate, I'm wanting to know if the 88 and 90 ECU are interchangeable? Also, any other info on what I might be able to check out in order to get the car running smoother? Only mods are BBK intake, O/R x-pipe w/ flowmasters and an MSD distributor cap w/ 8.5mm wires. I do also know that the smog pump was bypassed on the belt (guessing this was done since the car has the O/R x-pipe and won't pass smog anyway). TIA for the help.
[ July 06, 2012, 01:16 AM: Message edited by: BG50rider ]
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90 LX 5.0
Posts: 65 | From: Fairfield | Registered: Jan 2005
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Greasy
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Member # 5258
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posted
Get your TPS to .98V pull some codes and report back.
[ July 08, 2012, 02:10 PM: Message edited by: Greasy ]
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'93 Cobra-Coyote Powered
'03 DSG Cobra
'13 Dodge Cummins
'14 Rubicon X
Posts: 3272 | From: North Dallas | Registered: Jan 2005
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BG50rider
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Member # 5273
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posted
TPS set to .98v. Car runs strong. Still has a CEL. Connected the code reader to the plugs and CEL goes out. Disconnect code reader, and CEL comes back. ![[Confused]](confused.gif)
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90 LX 5.0
Posts: 65 | From: Fairfield | Registered: Jan 2005
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triple b
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Member # 8763
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posted
pull the codes engine off key on
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1988 4cyl conv 306 HCI "sasha"
2004 tahoe
Sold- 87 GT, 72 chevelle, 63 biscane, 82 monte carlo, 73 nova, 88 silverado,
Posts: 1730 | From: sacramento ca | Registered: Nov 2008
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BG50rider
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Member # 5273
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posted
Thats what I tried to do.
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90 LX 5.0
Posts: 65 | From: Fairfield | Registered: Jan 2005
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Greasy
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Member # 5258
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posted
Samething happens when you try to pull codes KOER?
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'93 Cobra-Coyote Powered
'03 DSG Cobra
'13 Dodge Cummins
'14 Rubicon X
Posts: 3272 | From: North Dallas | Registered: Jan 2005
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BG50rider
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Member # 5273
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posted
Let me try it...
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90 LX 5.0
Posts: 65 | From: Fairfield | Registered: Jan 2005
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BG50rider
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Member # 5273
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posted
With engine running, it still pulls no codes. The RPMs drop down around 700 or so with the code reader on and the engine running. Once unplugged, it takes about 30 seconds and the RPMs come back up to around 850. The light will stay off if you plug in the reader then start the car. If you start the car then plug it in, the light stays on. I am stumped.
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90 LX 5.0
Posts: 65 | From: Fairfield | Registered: Jan 2005
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triple b
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Member # 8763
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posted
sounds like a 4cyl swap gone wrong check ur vin to see it was a 4 cyl if so then they may have put the wrong wire harness in there it wil run but no codes cuz some wires are not correctly hooked up
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1988 4cyl conv 306 HCI "sasha"
2004 tahoe
Sold- 87 GT, 72 chevelle, 63 biscane, 82 monte carlo, 73 nova, 88 silverado,
Posts: 1730 | From: sacramento ca | Registered: Nov 2008
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BG50rider
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Member # 5273
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posted
Factory V8.
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90 LX 5.0
Posts: 65 | From: Fairfield | Registered: Jan 2005
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nitrous_bob
CAFords OG
Member # 77
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posted
did you try just using a jumper wire and counting flashes ? instead of the code reader ?
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5.0 OG since 1990
Posts: 1402 | From: st clair shores MI | Registered: Nov 2000
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