Real bad gas milage

[dogginred90]

I have a 1992 Z34 and it gets horrible gas milage. I am talking 10 mpg city. The things that have been changed within the last 1000 miles. Timing belt,fuel filter, plugs, wires, ICM(old one I had), LIM and UIM gaskets, thermostat,air filter, O2 sensor,EGR delete(still tuned for one),vacuum lines that was dry rotted or broke replaced, IAC sensor, and oil change. I am at a lose. The only thing I can come up with is maybe the cat is bad or injectors. Now my son does drive this and I can't say his foot doesn't have lead in it, but still should get better than that. Only got 128 miles on 13 gallons. Now one thing I ain't sure on that has me wondering. His trip odometer doesn't work. Could his odometer itself be off or are the separate from each other. Haven't torn the cluster out. Thanks guys. And welcome to w body GPF family

[digitaloutsider]

Odometer could be fucked.. use a GPS  speedo app like DigiHUD on your phone and make sure the mileage lines up. 

 

Does the exhaust smell rich?

[dogginred90]

I will try that. It does a little, but nothing extreme. It was a lot worse before I changed the O2 sensor.

[Galaxie500XL]

Well, there's no downstream O2 sensor, so unless the cat is blocked, it really shouldn't be a factor.

 

Two questions...how is the engine running?  Smooth? 

 

Also, are any codes being set?

 

Third thing... what O2 sensor did you use?  On my old LQ1, I didn't have much luck with anything other than an OEM sensor.  After I replaced mine with the OEM, I averaged around 20-21 MPG on my daily commute (70% interstate, 30% surface streets), and up to 27 with purely interstate travel.  If I drove exclusively on the surface streets, 17 was pretty much average.

 

EDIT:  I did find that over the years, I had to replace several coils...putting them on top of the exhaust manifold really wasn't such a hot engineering solution.

 

EDIT AGAIN:  But, I didn't buy new ones...I found later 3.1's/3400's, and got them, plus the ICM from junkyard cars--since they sit on top of the engine, they seem to live a much easier life.

Edited December 19, 2017 by Galaxie500XL

[Leadfoot]

A couple things before you put your head through the wall.  Did the mileage drop with the repairs you listed?  How does the exhaust smell?  Normal, rich, etc?  You really need to drive it some to see what the mileage is with normal driving behavior.  We were all teenagers once and it's amazing how driving habits can affect mileage.  I could certainly cause that car to get 10mpg with city driving when I was a teenager.  You need to verify that the problem isn't the loose nut behind the wheel    

[2001goldGTP]

Not sure this will translate over but i have had a rash of bad fuel pressure regulators causing the car to run rich and get horrible mileage. 

[dogginred90]

The engine runs smooth and the only code I get every once and a while is code 34 cause I deleted the EGR valve. I honestly don't know how this car should run with everything good on it. Ever since I have had it on the road(April this year). I have been fixing bugs the previous owner never fixed. Hence all the parts I put on it. For a 91,000 mile car, this thing had a lot of problems. The exhaust smells a bit rich, but not how it was before the O2 was changed. It is an AC Delco O2 sensor. And I know I was a teenager and I know I would of drove the wheels off of it. I am going to take it to work with me the remainder of the week to see how it does. 25 miles one way mostly highway. Should At least clean it out if anything

[Galaxie500XL]

Reminds me of the time my wife complained about the mileage she was getting out of our old 4 cylinder Mustang. I checked the mileage, 14 MPG.

 

Spent hours trying to find something wrong on my day off, and couldn’t find a thing. Next day, she wanted to go some place about 150 miles away, so I drove the Mustang—32 MPG, and I hadn’t changed a thing.

 

Found out after confronting her about the extreme difference that something other than the car was the problem. Turns out she was leaving late for work nearly every day, and was hammering the car to try to make up time.

Edited December 19, 2017 by Galaxie500XL

[mfewtrail]

The post above is something that shouldn't be overlooked. Drive the car yourself for a bit and verify if the mileage is bad or not. Also verify that the engine is getting to correct operating temperature.

 

As for the odometer, it's probably correct, but it wouldn't hurt to verify it as well. Either compare to another car or use the mile markers on the road of your choice. The trip odometer seems to fail somewhat commonly on 1st gen cars. There should be some old posts here on fixing it.

Edited December 21, 2017 by mfewtrail

[55trucker]

If possible get a scanner plugged into the system so you can do a real time monitor on what's going on.

 

You want to read what the A/F ratio constantly is displaying. Under all but full throttle you should be seeing 14.6-14.7, that would let you know that the mixture is correct. You also want to see what the injector pulse width is doing (1.9 is approx the norm at idle), the integrator reading should be near 128 all the time,..... the 02 sensor should constantly be sweeping back & forth between 0.2v & .9v depending on the current driving condition. Also what is the ignition advance reading? .....at idle it should be approx 20 degrees increasing to near 32 at off idle rpm.

 

Driving a *sick* car can & will kill the cat, if the fuel mixture is continually rich it won't take long for the cat to fail.

 

Where do you live??

 

Don't expect to get summer figures for fuel mileage in the middle of the winter. The colder the ambient air temp is outside the denser the air is so the MAP will adjust the fuel mixture to accommodate.

[digitaloutsider]

For clarification, the A/F ratio that comes off a scanner is a commanded A/FR. It'll tell you if something is commanding the wrong fueling, but it won't tell you what's actually happening. 

 

I agree the O2 reading is what you need to look at.

[White93z34]

I don't know what effect removing the EGR has on fuel trims if you haven't had the ECM adjusted for it to not be there

[dogginred90]

I wish I did have a scanner. I haven't had a chance to drive it to see whether it's him or the car. I live in Pa. I will be off for 10 days, so I will have time to look into more. I will drive it everywhere I gotta go and then fill it back up and see what I get.

[Imp558]

Where in PA?

[dogginred90]

Altoona

[Imp558]

Oh you're down there, I'm the other extreme as in I can see lake Erie by turning my head.

[dogginred90]

Yea I am down here. I turn my head and all I see is mountains in every direction.

[Imp558]

Looks like the truth table for the IAT and CTS are the same. Either can cause horrible fuel economy. If you just unplug them and read across the pins on the sensors with an ohmmeter it's easy enough to spot a faulty one.

 

If the CTS has 3 wires it will be the 2 pins that line up with the yellow and black wires. The green wire on a 3 wire sensor is for the gauge.

 

Sorry for the crapoopy image.

 

[55trucker]

A '92 LQ1 engine has 2 coolant temp sensors.

 

The ECM sensor is located on the bottomside end of the intake manifold under the throttle body, it is a two pin sensor. The sensor for the gauge is located in the back end of the forward cylinder head, it is totally obscured from sight by the engine lift support & the exhaust crossover, it is a single wire harness.

 

Nice graph on the sensor resistance slope. I take it that those readings are for the ECM sensor, too bad the FSM doesn't include that in it's information

[dogginred90]

Well it's not the best judge, but I put 80 miles on it so far. 50 miles highway and 30 city. And it is now sitting at 3/4 tank. I will do most of the driving till next fill up. But I bet it is him. A new issue though is that it cranks and cranks and then finally starts. Runs A bit rough at first then smooths right up and runs fine

[mfewtrail]

Well it's not the best judge, but I put 80 miles on it so far. 50 miles highway and 30 city. And it is now sitting at 3/4 tank. I will do most of the driving till next fill up. But I bet it is him. A new issue though is that it cranks and cranks and then finally starts. Runs A bit rough at first then smooths right up and runs fine

 

Any raw fuel smell or smoke from the exhaust when it finally fires?

[dogginred90]

I honestly couldn't tell. I didn't smell any raw fuel and as for smoke, it was dark when I drop e it the times it did it. I will see and smell more today when I drive it in daylight

[Schurkey]

I don't know what effect removing the EGR has on fuel trims if you haven't had the ECM adjusted for it to not be there

Fuel trim?  I'd be looking for spark retard based on detonation caused by lack of EGR.

 

My 3.4s both have spark retard based on damned piston slap.  24mpg highway is about the best they'll do.  I used to get ~28 highway @ 70mph  before the piston slap got so bad.

 

Altoona

I spent five weeks or so in Altoona, back in the early/mid '90s.  I liked the place.  There was a Mustang (Ford) parts supplier not so far from the motel I was at.  Forgot the name, but he sold heaps and piles of Mustang/Cobra replica parts. 

[Edit]  Tony Branda http://www.cobranda.com/info.html[/Edit]

 

Another business I remember was a certain bar that used a pair of guitars for a logo, one electric one acoustic, with the necks crossed.  Again, I don't remember the name of the bar--Sabastians?  Sebastino's?  Maybe something like that.

 

I was there because of the bus-testing track in State College.  The offices and repair center was in Altoona.  The company I worked for made city buses--one of ours was being tested at the time.  They were repeatedly breaking the sway-bars which was odd since that NEVER happened during regular service, but they sure popped 'em at the test-track.   The test-track was such a severe "torture test" that the sway bars were work-hardening, fatiguing, and breaking.

 

Culture Difference:  Took me a long time to figure out that the waitresses weren't being fresh...they called everyone "Honey".  That was new to me.

[dogginred90]

You are correct on both the Mustang supplier and the bar. And yes "Honey" is the norm here in Central Pa. And people also say we have our own accent in Central Pa. I dont hear it at all lol. Its not a bad city, but we are fighting to survive since the railroad is pretty much non existent.

[Leadfoot]

The extended crank and rough running initially points to something wrong.  That may or may not cause mileage as bad as your son is seeing.  His right foot might be part of that problem.  I would check fuel pressure.