I lost 3 MPG

drtdigger · 10-02-2009, 07:16 PM

i have a 1999 grand with a 4.0.the moter blew at 23600.No big deal i did my reserch and found 1 out of a 2000 grand 4.0. I did the swap and it runs like a charm. I've done all the plugs and filters. but ive lost 3 MPG. Is there a Tec in hear that could point me in the right direction?

Atl XJ · 10-02-2009, 07:48 PM

The 40l in my '96 died really early too. It did make it to 60k miles though, 23K is earlier than normal for a 4.0l. Its funny how many died such early deaths when others lasted 200k+.

MrBaz · 10-03-2009, 03:05 AM

Get it tuned? Sounds silly, I know, but it will usually get you better mpg.

eXcali · 10-03-2009, 03:59 AM

Quote:

Originally Posted by MrBaz

Get it tuned? Sounds silly, I know, but it will usually get you better mpg.

I agree, you should get it tuned. There could also be subtle differences between the model years. When you swap engines it takes the computer a couple weeks to a month to relearn all the trim levels etc. If your past that period I'd look at a good tune. Did you swap ECM/PCMs as well? If you kept the original you might check the part numbers on it to see if the new engine had an upgraded/flashed unit.

Also a motor blowing at 23k? That's very odd. What exactly happened to the original motor? The 4.0l is a pretty tough motor and can take quite a bit of abuse.

dcap63 · 10-03-2009, 08:42 AM

I'm guessing he meant 236,000.

xjaddiction · 10-03-2009, 09:36 AM

check catalytic converter...

mflueras · 10-03-2009, 11:01 AM

I have seen significant drops like that with failing O2 Sensors. There have been some emission changes from 99 to 00 that may cause an efficiency drop if the ECM has not been also replaced. Some ECMs need to be flashed at the dealer, also.

10-02-2009, 07:16 PM	#1
drtdigger Registered Join Date: Jun 2009 Posts: 1 Thanks: 0 Thanked 0 Times in 0 Posts	I lost 3 MPG i have a 1999 grand with a 4.0.the moter blew at 23600.No big deal i did my reserch and found 1 out of a 2000 grand 4.0. I did the swap and it runs like a charm. I've done all the plugs and filters. but ive lost 3 MPG. Is there a Tec in hear that could point me in the right direction?

10-03-2009, 03:05 AM	#3
MrBaz Registered Join Date: Oct 2007 Location: Colorado Springs, CO Posts: 803 Thanks: 0 Thanked 0 Times in 0 Posts	Get it tuned? Sounds silly, I know, but it will usually get you better mpg. __________________ 2004 WJ Charcoal Limited 4.7L H.O., QuadraDrive, Moonroof, NAV, tow package Goodyear Wrangler w/Silent Armor Tires Raybestos Advanced technology rotors w/ ThermoQuiet pads v3 headlights retrofitted w/fx35 projectors

10-03-2009, 08:42 AM	#5
dcap63 Registered Join Date: Sep 2006 Location: Staten Island, N.Y. Posts: 349 Thanks: 0 Thanked 0 Times in 0 Posts	I'm guessing he meant 236,000. __________________ '99 Laredo, 4.7, '04 Limited, 4.7 H.O.

10-03-2009, 09:36 AM	#6
xjaddiction Registered Join Date: Jul 2001 Location: TN. Posts: 510 Thanks: 0 Thanked 0 Times in 0 Posts	check catalytic converter... __________________ '98 ZJ 5.9L, 231 HD, TW shafts, 2" boost with 255x70x16's, ARB with MM winch, K&N cold air, just a start...

10-03-2009, 11:01 AM	#7
mflueras Registered Join Date: Dec 2007 Location: Hot Springs AR Posts: 452 Thanks: 1 Thanked 15 Times in 15 Posts	I have seen significant drops like that with failing O2 Sensors. There have been some emission changes from 99 to 00 that may cause an efficiency drop if the ECM has not been also replaced. Some ECMs need to be flashed at the dealer, also. __________________ ...a chicken...I'd slap a chicken... 1999 Cherokee 4 door, I6 AW4 242 8.25 the TOY 1995 Cherokee 4 door, I6 AX15 231 8.25 the PROJECT? 2000 Grand Cherokee Laredo, I6 242 SOLD (missed)

10-02-2009, 07:48 PM	#2
Atl XJ Registered Join Date: Sep 2004 Location: Colorado Posts: 8,382 Thanks: 15 Thanked 37 Times in 28 Posts	The 40l in my '96 died really early too. It did make it to 60k miles though, 23K is earlier than normal for a 4.0l. Its funny how many died such early deaths when others lasted 200k+.

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