3800 tune and mpg (Page 1/1)
Zachf1720 AUG 04, 02:30 PM
I have an 86 gt with the 3800 series 2 supercharged motor in it and right now it is only getting around 15 mpg with average driving mostly and the occasional pulls. It stales sometimes when you come to a stop with the clutch in and the rpms go up and down slightly at idle also, so i'm wondering if it needs a tune or if it is something else. The motor is stock right now with exhaust but i would like to go to a 3.4 pulley soon. I'm just wondering why it is doing the stalling, rpm thing and low mpg.
Dennis LaGrua AUG 04, 09:19 PM
Are your running a stock PCM program? If it is something is wrong. That engine should get 23-24 mpg city and 29 mpg highway. Have you done a scan of the PCM? Any number of sensors could be bad and a scan will get you closer to the problem. things like a leaky injector, fouled plugs, defective plug wires or even a dirty MAF sensor could cause bad mileage. Its difficult to tell what is wrong without doing the checks. First step, have you checked for DTC (trouble codes)?

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pmbrunelle AUG 04, 09:32 PM
Are you running a standard or automatic trans?

Edit; I saw this:

quote
Originally posted by Zachf1720:
stop with the clutch in


Question answered.

Well the 3800SC cars came with automatics, so the tune might need something different to work with a standard.

[This message has been edited by pmbrunelle (edited 08-04-2020).]

cam-a-lot AUG 04, 10:12 PM
Definitely not normal. Mine has a 3.0 pulley, intercooled, higher compression than stock, better cam, etc, and STILL it gets better fuel economy than it ever did with the stock 2.8 V6
Zachf1720 AUG 05, 01:30 AM
The car came with like 3 pcms and I think the guy that had it before thought that changing the pcm would fix some electrical problems that it no longer has. So the pcm that is in it right now is not stock to my knowledge. Is tuning it something that would be ok if it was mailed off or is it better to do it in person.
hnthomps AUG 05, 03:55 PM
There is certainly some sort of problem to get mpg that low. I have a basically stock 3800 SC Series II with a 3.4 pulley and a Getrag 282 transmission. I generally get around 26 mpg with a very conservative tune that dynos at about 258 hp and 300 ft lbs of torque at the wheels.

Nelson
fierosound AUG 05, 07:53 PM

quote
Originally posted by Zachf1720:

I have an 86 gt with the 3800 series 2 supercharged motor in it and right now it is only getting around 15 mpg with average driving mostly and the occasional pulls. It stales sometimes when you come to a stop with the clutch in and the rpms go up and down slightly at idle also, so i'm wondering if it needs a tune or if it is something else. The motor is stock right now with exhaust but i would like to go to a 3.4 pulley soon. I'm just wondering why it is doing the stalling, rpm thing and low mpg.



I've seen people with their vacuum lines connected wrong.
All kinds of odd engine problems.

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