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1989 Terrible Gas mileage!


Guest UncleCharlie

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Guest UncleCharlie

Well, Recently my 300zxTT got stolen, and I needed a car, Just so happened the Reatta that my dad drove when I was a teenager had been parked on the back lot for a few years and he said, get it out of here. After being parked (Because of a failing fuel pump) for 5 years, all I did was replace the pump, fill it with gas, and we drove it to go get the tags. Since it's resurrection, It's had an oil change, new plugs, new wires, new coils, brakes, fuel pump, thermostat, air intake, exhaust, and ecm. As of today, I have had it on the road for about two months, and have around 2k miles on it, the odo is currently at 115k, and for some reason I'm averaging 10 mpg on the freeway.

It doesn't seem to be throwing any ecm codes, and the only bcm codes it's throwing seem to be for the headlamps (It has the front clip from a riviera, so no pop up headlamp motors ect).

Any suggestions as to how to troubleshoot this would be appreciated.

post-92838-143141860777_thumb.jpg

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Are several things that can cause bad MPG (though that is really bad, any chance of a leak ?) Since it has had a major tune up & if it seems to be running well, best to take a snapshot when cruising at about 45 and let us take a look at the readings.

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Guest UncleCharlie
Welcome UncleCharlie! Are you calculating the mileage based on miles driven compared to gallons used or going on the digital readout for MPG? Digital readout could be off.

Digital readout it at 10.3, and gal vs. miles driven is about the same. I get 55 miles to 5 gallons

Also, What do you mean by snapshot?

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As noted by Padgett, there are several things that can ruin the gas mileage. You could have more than one problem.

You might want to start by cleaning the MAP sensor, you can purchase spray cans of cleaner.

A common problem is the cam sensor......actually the magnet. The magnet is held in the end of the cam with a plastic retainer. With age the plastic can fail and the magnet falls out. Since the sensor cannot sense the magnet, the engine goes into a "limp home mode" it will run but the ECM is not firing the injectors on a timed sequence, they are squirting fuel all the time, leading to the bad gas mileage.

I had a "knock sensor" go bad and it was sending a signal to the ECM. The ECM thinks the engine is knocking and adjust the timing and possibly the injectors. In my case, the car idled poorly, lacked performance, and had bad gas mileage.

These are just some of the possibilities.

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Does everything seem smooth? Plenty of good smooth power? I had a bad coil pack on an '89, the misfire also clogged the catalytic converter. Replaced the cat, coil/icm, plugs and wires and it ran like a champ. Before the new parts I was getting 10-11

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Snap shot

Look at your CRT [tv screen]. Press the "climate" button. Press the "off and "warm" buttons at the same time to go into diagnostics. Scroll to BCM and then scroll to Snap shot. Drive car to 45 MPH and press button to lock it in. Pull over to side of road and write down the info and report back.

BTW regarding your Reatta with the Riviera front end. Did your dad do that and was he a visitor to this forum. If so what did he use for his forum name?

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Guest UncleCharlie

Yeah, my dad was on this forum for a long time. He's the man responsible for the front clip. He said it was known as "The Riveatta" lol

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Guest UncleCharlie

Alright. I believe I've done it.

No ECM codes

B119 current

B122 History

B123 Current

B440 History

B448 History

B552 History

C553 History

I don't know his user name, His name is Alex though.

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I knew it! Went by the name of alexhouston. Sold me a wood grain console for my Reatta. That was before I figured out I could buy what I needed at Gibson's. How is he doing? If I remember he broke his leg, which was one of the reasons why he got out of Reattas...

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Guest Mc_Reatta

That flat Riveatta front end will take some MPGs off the top at speed.

Didn't see a new O2 sensor in the mix. A bad one can cost some MPGs too.

How does the engine run when driving, idling?

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Your two current codes are photo cell and instrument cluster, which could be tripped because of the Riv front end. They have nothing to do with performance.

I would guess that you may want to change the oxygen sensor, clean the IAC [idle Air Control] and MAF [Mass Air Flow] Sensor. None of the afore mentioned items will trip a code, but will affect gas mileage. Also if you can remove the Honeycomb screen [remove the rubber tube from air box to intake. Then remove snap ring holding Honeycomp disc in place] on your air intake you can use some carb cleaner and a toothbrush and a rag to clean the butterfly.

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Guest Mc_Reatta
Alright. I believe I've done it.

No ECM codes

B119 current

B122 History

B123 Current

B440 History

B448 History

B552 History

C553 History

.

First three are related to the panel lamps and dimming circuit.

The next two AC related

The last two are from disconnecting the battery probably when the ECM was replaced.

Have you driven far enough yet for the new ECM to learn the engine responses?

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Since you mention changing plug wires I think you should check carefully for crossed spark plug wires. Not too many things can account for such a huge drop in mpg but crossed spark plug wires certainly could. NC's idea about checking for a plugged converter is a good one.

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Guest UncleCharlie
I knew it! Went by the name of alexhouston. Sold me a wood grain console for my Reatta. That was before I figured out I could buy what I needed at Gibson's. How is he doing? If I remember he broke his leg, which was one of the reasons why he got out of Reattas...

Yeah, He had a pretty bad spill, broke his leg and hip, He's doing alright, fixing up a 1927 Hudson super six right now. He finally completed the 91 white/Burgandy convertible to all of it's original glory, although it took him FOR EVER to find all the interior trim in burgandy. But yeah, he's still around restoring classic cars and tractors, and I guess he figured it's my turn to play with the Reattas. He claims he's not into the Reattas anymore, But he can still be spotted taking his convertible out of the barn for a wash on occasion. lol

And @ MC_Reatta It idles fine, when I first started driving it, it had some stuttering/hesitating throttle at take off, and also at 1700-2k rpm. Since the tuneup it seems to have disappeared, I dismissed it as a bad plug wire or coil.

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Bad O2 will propbably not have any cross counts or very few - should be 10-12 at 45. Knock sensor will send OldPA3 through the roof should be low three digits max and not climbing at 45. Snapshot is of all the engine parameters (over 20) and reached through diagnostics.

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Guest UncleCharlie

@Ronnie - The car isn't running cats, they were plugged when I got the car, so they've been chopped. I've referred to the shop manual and it seems that my plug wires are correct. Also, the mileage was bad before the cats were ditched and plugs and wires were replaced.

@ padgett - I'm still getting used to this diagnostic system, which I must admit is a bit confusing at first, my dad has some experience with these cars, I'll get him to show me how to do the snapshot when he gets back into Houston tomorrow and get a proper readout to post up. Also something to note, When I press "Diagnostic" button, (Not going into the actual diagnostic mode) it seems that EVERYTHING I select reads up an error. For example, it will tell me that the door is open, when its not, says the car is overheated, when its at 120 degrees etc.

I have to go down to auto parts in the morning anyway, so I'll pick up an O2 sensor while there just for the heck of it. Worth mentioning, I'm running a 180 degree thermostat and ecm. Also, I cleaned the butterfly, Swapped the MAF with a known working one, and cleaned the MAF housing tube (The thing that attaches to the throttle body with the honeycomb in it.)

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UC,

When I press "Diagnostic" button, (Not going into the actual diagnostic mode) it seems that EVERYTHING I select reads up an error. For example, it will tell me that the door is open, when its not, says the car is overheated, when its at 120 degrees etc.

You are not the first one to be fooled by this system.

Check out this link:Why is diagnostics telling me I have so many problems? - Reatta Owners Journal

The Reatta Owners Journal (ROJ) is repository of Reatta information.There's a bunch of friendly guys there ready and willing to help a guy (gal) out. You should sign up over there to have access to a wealth of info. The site owner is a great guy and very helpful. His name is Ronnie.

John F.

Edited by Machiner 55 (see edit history)
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I am also running a 180 with fans programmed to come in earlier. Have not touched the advance or fuel maps. Typically I get about 18 around town on 87 PON and have seen 27 on the road (25 more common - speed dependant).

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I am also running a 180 with fans programmed to come in earlier. Have not touched the advance or fuel maps. Typically I get about 18 around town on 87 PON and have seen 27 on the road (25 more common - speed dependant).

I'm running no mods, but get 21 around town, and 29 on the highway. Also know I need to change the can magnet.

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Guest UncleCharlie
UC,

You are not the first on to be fooled by this system.

Check out this link:Why is diagnostics telling me I have so many problems? - Reatta Owners Journal

The Reatta Owners Journal (ROJ) is repository of Reatta information.There's a bunch of friendly guys there ready and willing to help a guy (gal) out. You should sign up over there to have access to a wealth of info. The site owner is a great guy and very helpful. His name is Ronnie.

John F.

Wow, haha, So it's a repository of simulated error codes? I think I have my homework cut out for me in this car. lol

By the way, about to pick up the O2 sensor, and see my dad about getting the snapshot readout.

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Guest UncleCharlie

Well, sure enough, I unplugged the battery, Popped in a new O2 Sensor, then went for a cruise. I drive 10 miles city then 15 miles on the Highway. I hit 27 MPG and it was still CLIMBING. post-92838-143141862337_thumb.jpg

post-92838-143141862321_thumb.jpg

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