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Fuel economy dropped since replacing faulty ICM by My88RedGT
Started on: 04-10-2015 12:37 PM
Replies: 7 (171 views)
Last post by: My88RedGT on 04-10-2015 08:36 PM
My88RedGT
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Report this Post04-10-2015 12:37 PM Click Here to See the Profile for My88RedGTSend a Private Message to My88RedGTEdit/Delete MessageReply w/QuoteDirect Link to This Post
My fuel economy has dropped from 27 to 21MPG after replacing a ICM the died when it got hot. Engine no longer dies since replacing the ICM and going through 3 tanks of fuel. I got the timing set to 10 degrees BTDC as instructed on the label on the desk lid... ALDL was jumped across A-B and vehicle in drive. Idle is rock steady and no pinging from engine. Vehicle runs like a brand new car with the exception of the fuel economy.

ICM installed came from Cardone distributor. Could this ICM be the reason my mileage sucks compare to the mileage with the old ICM that died?

I had a new Cardone 84-1633 on hand when the original ICM died, so I used that ICM.

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Report this Post04-10-2015 02:33 PM Click Here to See the Profile for TopNotchClick Here to visit TopNotch's HomePageSend a Private Message to TopNotchEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'm pretty sure that timing should be adjusted with the vehicle in neutral. "Vehicle in drive" indicates you have an automatic, so make sure your torque converter is locking up at highway speeds. An easy way to tell is to try to accelerate a little while driving at highway speed. Engine RPM's should not increase unless the car's speed increases. If the engine RPM's increase without the car going faster, your torque converter is not locked up, and that will cost you MPG.
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My88RedGT
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Report this Post04-10-2015 03:18 PM Click Here to See the Profile for My88RedGTSend a Private Message to My88RedGTEdit/Delete MessageReply w/QuoteDirect Link to This Post
I do have and automatic. 4t60 to be exact.

Torque converter is locking up at highway speeds. My rpm is about 2300 at 75 mph.

Is there a difference in ICMs. Ex. Performance vs stock?
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Gall757
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Report this Post04-10-2015 03:53 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
I am not one for throwing parts at a problem, but in this case I would replace the O2 sensor, because:

A. It's cheap, and it can't hurt
B. If it is unable to detect small changes in fuel mix in the exhaust, the computer will not send less fuel to the injectors....which is what you want.
C. I can't figure out a way to trouble-shoot low mileage.

edit: I have not heard of any variation in ICM construction, but a good one might send much stronger signals than a bad one.

[This message has been edited by Gall757 (edited 04-10-2015).]

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theogre
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Report this Post04-10-2015 04:24 PM 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 My88RedGT:
I got the timing set to 10 degrees BTDC as instructed on the label on the desk lid... ALDL was jumped across A-B and vehicle in drive.
jump AB is good but in drive? no.
Reset timing in park/neutral.

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Gall757
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Report this Post04-10-2015 05:31 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by theogre:
jump AB is good but in drive? no.
Reset timing in park/neutral.


The GM sticker writers disagree.

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My88RedGT
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Report this Post04-10-2015 08:31 PM Click Here to See the Profile for My88RedGTSend a Private Message to My88RedGTEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'll replace the O2 sensor I guess... It was replace 2 yrs ago due to failure.

I connect my Actron diagnostic scanner and no codes are stored. I did run a real-time analysis on it with the scanner and the O2 sensor is alternating between rich and lean. The system is going into closed loop, the running temp is 210˚F . MAP sensor voltage is approx 1.35v according to the scanner. I already replace the thermostat with new 195˚F and IAC. I pulled #1, #3 & #5 spark plugs and they look normal. Plugs and wires are about 2 years old with about 8k miles on them. I replaced the coil since I had a spare too.

I called a trusted mechanic friend of mine and he is baffled as well.

Engine does not ping even with 87 octane.

I'm usually not one for throwing parts in hoping to fix an issue, but I'm coming up with nothing else to try.

My emissions need testing here in May and with economy sucking, I hope it will pass this time.

Guess it's time to get a AC Delco ICM and try that.
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My88RedGT
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Report this Post04-10-2015 08:36 PM Click Here to See the Profile for My88RedGTSend a Private Message to My88RedGTEdit/Delete MessageReply w/QuoteDirect Link to This Post

My88RedGT

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Member since Aug 2013
One more thing... Would changing the time to say 12˚ BTDC make a difference in economy?

I know it's suppose to be 10˚ BTDC, but if the engine is running without knocking, I wouldn't thinks it would hurt.
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