My poor mileage problems (Full Version)

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My poor mileage problems

Blazin_Jason -> My poor mileage problems (12/19/2007 7:34:41 PM)
Looking for some advice from the more experienced members here. 89 4.3 TBI (I think Z code) non "vortec" engine. Since I bought the truck a couple months ago I've done a seafoam through the intake, replaced distributor (set timing with ESC disconnected etc), plugs, wires, fuel filter, air filter, synthetic oil change (no cat as that was removed before I bought it). The truck runs pretty good, idles fine no major issues, just very poor mileage. The truck seems to run rich and the exhaust smells. I want to figure out what to check, test, and possibily replace if needed. Where should I start? Thanks Jason

RCars2 -> RE: My poor mileage problems (12/20/2007 8:52:27 AM)
I would be somewhat concerned about the cat being gone. Im not entirely positive on this as i havent had an opportunity to crawl under a 1st gen but there should be a post cat o2 sensor. Whoever removed the cat probably either put a dummy sensor in or probably just has it dangling somewhere under the truck. The engine could be trying to compensate for that which could be part of your issue. Definately though having no cat is accounting for the smell.

swartlkk -> RE: My poor mileage problems (12/20/2007 10:37:15 AM)
OBD1 s-series trucks (pre-95) did not have any catalytic monitoring O2 sensors, IIRC.

RCars2 -> RE: My poor mileage problems (12/20/2007 12:28:07 PM)
Hmmm, i stand corrected then. For whatever reason i thought the OBD1's had those sensors.

swartlkk -> RE: My poor mileage problems (12/20/2007 1:22:12 PM)
I think what you are thinking of is the pre-cat sensor that is found on some of the later '95 trucks and on the '96-'97 trucks. All '95-present have a post cat sensor that monitors the catalyst. Even in an OBD2 vehicle, if the cat were not present, it would trigger an SES light. It would not affect the operation of the engine at all.

drperry -> RE: My poor mileage problems (12/20/2007 1:22:59 PM)
Nope... OBD1 vehicles usually only had one O2 sensor... Maybe the injector leaks a bit.. What kind of bad mileage are we talkin' here?

Blazin_Jason -> RE: My poor mileage problems (12/20/2007 4:39:42 PM)
Well when I fill up tomorrow I will have a better idea. Roughly I was getting about 250km's to about 3/4 tank or so. There does appear to be an O2 sensor just after the y-pipe in the exhaust. Kyle do you have any insight? Should I check the ECM coolant sensor, 02 sensor, injectors, fpr? I just don't want to through to much money at it unless it's required.

drperry -> RE: My poor mileage problems (12/20/2007 5:08:36 PM)
That's like 13MPG... For city driving in the winter... That's pretty close...

swartlkk -> RE: My poor mileage problems (12/20/2007 6:26:49 PM)
It is quite difficult to come up with a mileage with the information given. You should fill up until the pump clicks off and go no further. Drive it until you are ready to fill up again. When you fill up again, write down the distance travelled and the quantity of fuel to fill it up to the same point. Use the same pump if you can. Then let us know the distance and quantity of fuel required to fill your tank back up. This is a TBI motor so you don't have an FPR, atleast not in the sense of one that is internal to the engine. Lets get an accurate baseline for the mileage and we'll move forward from there. But it is quite possible that the O2 sensor is to blame. It shouldn't be all that expensive for your truck...

Blazin_Jason -> RE: My poor mileage problems (12/20/2007 6:39:13 PM)
I wrote down the mileage last time I filled up, which is basically all highway this tank. So tomorrow after work I will fill it up and will have that information. What I have noticed if that I am down over 100km's or so between fill ups. I know not accurate, but it was quite noticeable.

drperry -> RE: My poor mileage problems (12/21/2007 3:29:07 AM)
Before I did the cap + rotor on my truck, I was doing about 200 - 250KM for every 45 - 50L of gas... before the cap + rotor wore out, I was getting over 300... but that was in the summer, lol. so far, it looks like I'll be getting about 300km out of the same amount of fuel... and that's not babying the truck...

blznlowxtreme -> RE: My poor mileage problems (12/21/2007 7:13:51 AM)
whats up w/ this KM and L? thats like a metric system or something. lol i have no idea what that converts into in miles and gallon.

rriddle3 -> RE: My poor mileage problems (12/21/2007 7:17:52 AM)
That's right, it is metric, they are Canadians and use that system. Here's a link to online conversion programs you can use to get the figures into our system.

swartlkk -> RE: My poor mileage problems (12/21/2007 7:41:57 AM)
Here is a conversion utility that is geared directly at mileage conversions, just pick the appropriate conversion you want to make --> CLICK HERE So drperry, lets average that out and your 200-250km = 225km and you 45-50L = 47.5L which translates to a 21.1 L/100km (100 * 47.5 / 225). Using the utility above, that equates to 11.1 miles per US-gallon.

blznlowxtreme -> RE: My poor mileage problems (12/21/2007 7:50:14 AM)
ok thsnks, loking at how swartlkk done that math, 11.1 mpg is not too good

swartlkk -> RE: My poor mileage problems (12/21/2007 7:57:59 AM)
If you take drperry's updated mileage of 300km per 50L, that would translate to a 16.67L/100km or 14.1 miles per US-gallon. If it were 300km per 45L, that is 15L/100km or 15.7 miles per US-gallon. This is quite plausible for winter time driving and/or not being kind to the accelerator pedal.

rriddle3 -> RE: My poor mileage problems (12/21/2007 8:57:57 AM)
What is it about winter up north that cuts down on mileage? Down here in winter engines run better and mileage increases. It's summer that kills us because we have to run the a/c constantly.

swartlkk -> RE: My poor mileage problems (12/21/2007 8:58:50 AM)
Additives in the fuel to improve cold starting.

drperry -> RE: My poor mileage problems (12/21/2007 1:47:49 PM)
Yeah, I didn't drive my Blazer very nice while it was in need of cap + rotor... For the record, I normally use MPG, and didn't have any conversion programs for converting MPG to L/100km... My dad is old, so I learned MPG, lol. Mostly, the only additive they put in the fuel is gas line antifreeze, I think... Depending on which gas station you visit. You don't want your gas lines freezing up at -40, lol.

Hanr3 -> RE: My poor mileage problems (12/21/2007 3:57:21 PM)
Back to the original poster. Disconnect the 02 sensor and see it that makes a difference in your gas mileage? If not, your 02 is shot and needs replaceing. Once the truck warms up the puter goes into closed loop mode and reads the 02 sensor. If the 02 isn't providing information the puter goes into defualt mode. It'll run, however your gas mileage will suck. The other thing is your engine temp sensor. Not the gauge temp sensor. If the engine temp sensor isn't sending the proper temp to teh puter it will never go into closed loop and it will never look for the 02 reading, again the effects is your gas mileage will suck, and if you have a '93 or later truck with the 4L60E puter controlled tranny your tranny will never go into lock up mode and you risk frying it. The puter uses the tranny heat to shorten how long it takes to get the engine up to operating temp. The puter doesn't monitor tranny temp, so it could get dangerously hot and you wont know it.

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