11.4mpg in town in my '89 L98.

[c4steve]

'89 Red vet,auto,3.07,97k......

A simple quick question.... I personally think somethings wrong... This thing runs like a beast (good).... Yet even P***y foot'in this thing I can only get between 11.4-12 mpg in town and this is NOT racing from stop light to stop light.... I'm just trying to get to work.... Is this normal or WTF??? BTW I have FIC B3 injectors,new regulator,new filter,and new pump/screen/wires... Not to mention a complete and full tune up.

Is this normal... I can get very low 20's on the highway in OD....

Any suggestions?

Thank you.

 

[G Winter]

Doesn't sound right. You should be able to bet at least mid 20s on highway. Are you going by the trip computer or by the actual gals and miles ? Welcome to the site.

Glenn

 

[Dustoff529]

That is a PROBLEM.. my 90 6 spd gets 25 - 27 on the road! BETTER than my wife's Maxima!

When I have your wounded
Charlie

 

[Baldie88]

I have a red 88 that is probably pretty much a clone of what you have (auto and 3.07). Only I have about 51K on it. Even idling a lot in a parade and a lot of city driving the worse I've ever gotten is about 17 mpg. I keep track of all my mileage and I range anywhere from 17 to 26 mpg depending on city/highway driving.

I don't know what the problem might be but this is what I'm getting with mine.

Hope this helps.

Ron
"Baldie88"

 

[koolaid117]

I average 17.7 when I am driving normal on my daily drive to and from work and that is all city driving.

 

[Schrade]

'89 Red vet,auto,3.07,97k......

A simple quick question.... I personally think somethings wrong... This thing runs like a beast (good).... Yet even P***y foot'in this thing I can only get between 11.4-12 mpg in town and this is NOT racing from stop light to stop light.... I'm just trying to get to work.... Is this normal or WTF??? BTW I have FIC B3 injectors,new regulator,new filter,and new pump/screen/wires... Not to mention a complete and full tune up.

Is this normal... I can get very low 20's on the highway in OD....

Any suggestions?

Thank you.

Your fuel trim is max'ed. That means no matter the throttle position, the computer is keeping the injector pulsewidth OPEN for MAX fuel delivery. Drive slow, you're not using it all, and going nowhere as the fuel max'es. Low mileage. Highway speed, fuel is stil max'ed, but you're covering some real estate, mileage goes up.

Your cats will foul quickly with FT max'ed. Do you have any codes? You know the paper clip trick?

If no codes, is it loping idle/surging at stoplights?

If no surging/loping idle, search my posts for fuel pressure tests, and follow EXACTLY for procedure.

 

[tonylong]

'89 Red vet,auto,3.07,97k......

A simple quick question.... I personally think somethings wrong... This thing runs like a beast (good).... Yet even P***y foot'in this thing I can only get between 11.4-12 mpg in town and this is NOT racing from stop light to stop light.... I'm just trying to get to work.... Is this normal or WTF??? BTW I have FIC B3 injectors,new regulator,new filter,and new pump/screen/wires... Not to mention a complete and full tune up.

Is this normal... I can get very low 20's on the highway in OD....

Any suggestions?

Thank you.

I'm getting about the same as you. I get 14-15 mixed hwy/town, and 21-23 interstate. It's always been like that. 89 vert, auto, 70,000 miles.

 

[c4steve]

Thanks guys I didnt think something was right. Yesterday I went and filled up and after some calculationg it came out to like 11.758xxxx mpg. It has no codes,but it does surge a bit at idle,not sure if this is within the same problem but unless warmed up (around 110f),somewhere between 900-1100rpms it'll get a tiny shake while accelerating from a stop but if you stab the pedal the car takes off.... I ran a fuel pressure test and it came back right at 42 and didnt drop more than 3-4 psi while idling... The exhaust does smell a bit gassy (no smoke though) and I'm pretty sure my cat/pre cats are stock.

What controls this fuel trim thingy btw?

Thanks .

 

[Schrade]

Thanks guys I didnt think something was right. Yesterday I went and filled up and after some calculationg it came out to like 11.758xxxx mpg. It has no codes,but it does surge a bit at idle,not sure if this is within the same problem but unless warmed up (around 110f),somewhere between 900-1100rpms it'll get a tiny shake while accelerating from a stop but if you stab the pedal the car takes off.... I ran a fuel pressure test and it came back right at 42 and didnt drop more than 3-4 psi while idling... The exhaust does smell a bit gassy (no smoke though) and I'm pretty sure my cat/pre cats are stock.

What controls this fuel trim thingy btw?

Thanks .

Some things control fuel regardless of what's going on with the motor, like the MAF, and some things control fuel by what's coming OUT of the motor.

When things go wrong tho', they can work against each other, and fuel mileage goes down the toilet.

Surging idle, you say? When warmed up? Like at stoplights?

 

[c4steve]

I'll research up on testing some of those sensors (I gotta quit being a cheapo and get that fsm). And the surging at idle when warmed up is real slight and only say,every 3-5 seconds. When it surges its slight as well but happens in the low rpms when taking off from a stoplight but then smooths out and shifts,accelerates smooth and such.

 

[Schrade]

I'll research up on testing some of those sensors (I gotta quit being a cheapo and get that fsm). And the surging at idle when warmed up is real slight and only say,every 3-5 seconds. When it surges its slight as well but happens in the low rpms when taking off from a stoplight but then smooths out and shifts,accelerates smooth and such.

3-5 seconds cycle loping idle is textbook indicator of vacuum leak. Search my posts for vac leak detection.

 

[c4steve]

Will do,thank you very much friend .

 

[89blackvette]

That is BAD mileage. My 89 6 speed gets 25 to 26 on highway and 22 in town. YOU GOT A PROBLEM! Just my 2 cents I would check the TPS (Throttle position sensor) first, it is easy to get to and test with a meter. Get the Factory Service Manual, since you have a C4 it will be worth it's weight in gold. Listen to the guys here they will help you and guide you in the right direvtion. Welcome and good luck with it.

 

[ex-x-fire]

Things to check for when you are getting bad mpg.
1. Is your engine running cool? 190* to 200* is normal temp. while driving. So many guys out there are brainwashed into thinking a stock t-stat is to hot. An EFI engine has no choke, so the ecm uses the coolant temp senser to richen it up, driving around with a 160* t-stat is like having the choke half closed. Also check the resistance of the coolant temp senser at operating temp, around 190-200 ohms. Unless you can scan it, check the gauge & cts for similar readings.
2. Ok you did a fuel pressure check, does it hold pressure when the engine is off? Pull the vacuum hose off the reg. no fuel should be present.
3. Check for vacuum leaks & hook up a vacuum gauge to it, on stock type cammed engine you should get 17 inches or more at idle. Needle should be steady.
4. Check your timing, does it advance when you rev it? You can run more timing(10*-12* is a good starting spot) but you may have to run premuim gas.
5. Clean maf senser, I don't know if your running a K&N air filter, the oil on the filter sometimes coats the wire in the maf.
6. O2 senser, I read some where that if you jump the A & B terminals at the dianostic connector, on fully warmed up running engine, the check eng. light will flash for evertime the O2 switches back & fourth(rich to lean). It should be active & flash kinda quickly, these ecm are slow though, rev it up, it should slow down flashing while under load.
7. Check the grounds, I've seen cars run funny w/ loose or dirty grounds. There is one on the head, near the firewall, that is for the ecm I think.
8. Egr valve, check for proper operation, put a vacuum pump on it, the engine should stall/run rough when it opens at idle.
Hope this helps, good luck.