2.3L ('83-'97) Low mpg


Slowestranger88

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When I got the truck it had pretty great gas mileage even when it was on 31/10.5 tires. And just recently I can’t drive more than 50 miles without burning through 3/4 tank. I replaced spark plugs/wires 2 months ago. Took it to a shop before all this happened and had them check my timing to make sure I had it right. Just did O2 sensor. Has stocks on it now and that didn’t seem to help. Also I don’t know if they’re all as gutless as mine but man, getting it to 70 is a mission. Any ideas?
 


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Slowestranger88

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Probably should’ve said. It’s a 88 2.3 regular cab short bed
 

Slowestranger88

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Also should’ve stated that it is the 4 speed with o/d
 

Josh B

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When I first got mine it ran very well. I changed the plugs and wires, the coil pack, the O2 sensors, the oil, the transmission fluid, just all sorts of simple preventative maintenance I wasn't sure of.
After running some motor flush in the oil, and seeing gobs of crud come out, I thought I had it just about under control.

Then it started running like crap and guzzling gas like crazy, no power, spitting back, horrible.

I went all through the thing not knowing what to do, you could read about it in my 96 Explorer thread.

After a couple months and not seeming to get any closer to fixing it I stopped one night in the dark, after a number of miles at 70 and looked at the catalytic converter, it was so hot I could almost see through it.

I tried to pull it out and soak it in soapy water a couple days and flush it with the water hose but the first forward bolt I twisted plum broke off.

I didn't have any replacement bolts, not sure that stud will even come out, they come pre-installed on the forward flange.
I'll get another one maybe in March so now I'm just putting it around, it don't do so bad if I stay off the gas a bit.
 

scotts90ranger

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That is a reasonable thought... catalytic converter failure can happen once they get to about 900C for anything more than a few minutes... main causes of that are misfires which would be ignition related where there is an air fuel mixture that is not burned until it reaches the high temperature of the catalyst. The misfires can be from cracked or fouled spark plugs, bad TFI module, bad cap or rotor, etc, mainly spark... the bad thing is to have a bunch of air and fuel that is not burned so that means the fuel injectors are working. It's not lack of oxygen or too much fuel as that would just go through, more fuel than air just puts the fire out, it has to be a mix of fuel and air...

That said, I see you changed plugs and wires, what about cap and rotor? Usually if there's a TFI problem they cause no spark so not likely... same with module in distributor...
 

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cat converter sounds possible, checked compression? I had a converter plug on my ‘88 (very long time ago) and ended up with exhaust valve damage on 2 cylinders.
 

Slowestranger88

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I did replace cap and rotor when doing the wires. I went down to the exhaust shop yesterday and cut the car out (ordered a new one so I didn’t have to pay 300) I’ve only driven the truck about 20 miles since then so hard to tell but the cat did look kinda plugged. High hopes.
I probably should compression check the motor. It had some complications for a while (bad timing) but it’s all cleared up now. Now just hoping I can figure out the mpg problem. Do you think that the rear main could cause any of this? I’m going to be replacing it next weekend when all the parts get here
 

scotts90ranger

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It kinda sounds like the timing trouble you were having could have taken out the cat, if you now have more power the mpg should come back with it to some extent at least.

I would still do a compression test, should give some resemblance of an engine state of health... I need to do that to the '97 just for good measure, it has what seems like good power but seems doggy at times... a leak down test is better than compression but compression is way easier and just doesn't tell the source of the issue...
 

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Alright so I have a general idea on mpg now. I drove to get gas (right next to work) filled her up. Then parked at work all day. Drove home which is exactly 2.7 miles from my house (lucky me) then drove back to work this morning. 1/4 tank gone. Idk what’s going on but it’s horrible
 

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Cats in my experience don't decimate MPG that badly when they go. The O2 sensor is in front of the cat in the exhaust stream so it can't read any differently whether the cat works or does not.

Your 1988 truck's injection system calculates how much fuel to inject using a method called speed density. Speed density takes manifold air pressure, temperature, O2 sensor feedback and RPM to calculate the prospective air/fuel ratio and adjusts the TFI & fires injectors accordingly. How new is your MAP sensor? How about your PCM's own (different) tach sensor? Intake air temp sensor?

Other things that impact the AFR when they go:
- PCV valve
- EGR valve
- Vacuum leak
Good news. These are all easy.
- Soak the PCV in some carb cleaner for a few hours, blow it out, rinse it, put it back in and you're good.
- Grab a piece of vacuum line and hook it onto the EGR valve. Suck on the other end as hard as you can. If the engine quits, your EGR works.
- Test for vac leaks with whatever you're smoking in the shop. Hold something that's burning up next to lines, and if you see suction pulling smoke in, there's your leak. You should also hook up a vacuum gauge to various lines and see if they are close to baseline manifold vacuum at idle.

Rear main seal holds oil in. When they fail, oil gets out, thats about it. Not going to kill MPG.
 

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Another thing to try. Set the key to Run and climb under the truck. Smell around. Look for fuel leaks. Then start the truck and do the same. You could be leaving a barely noticeable trail of the good stuff behind you.
 

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Cats in my experience don't decimate MPG that badly when they go. The O2 sensor is in front of the cat in the exhaust stream so it can't read any differently whether the cat works or does not.

Your 1988 truck's injection system calculates how much fuel to inject using a method called speed density. Speed density takes manifold air pressure, temperature, O2 sensor feedback and RPM to calculate the prospective air/fuel ratio and adjusts the TFI & fires injectors accordingly. How new is your MAP sensor? How about your PCM's own (different) tach sensor? Intake air temp sensor?

Other things that impact the AFR when they go:
- PCV valve
- EGR valve
- Vacuum leak
Good news. These are all easy.
- Soak the PCV in some carb cleaner for a few hours, blow it out, rinse it, put it back in and you're good.
- Grab a piece of vacuum line and hook it onto the EGR valve. Suck on the other end as hard as you can. If the engine quits, your EGR works.
- Test for vac leaks with whatever you're smoking in the shop. Hold something that's burning up next to lines, and if you see suction pulling smoke in, there's your leak. You should also hook up a vacuum gauge to various lines and see if they are close to baseline manifold vacuum at idle.

Rear main seal holds oil in. When they fail, oil gets out, thats about it. Not going to kill MPG.
When my driver's side cat was going bad, my fuel mileage actually went up by a large amount, as in it got a lot better before codes started coming up. Like in going from an average of around 18-19 mpg to 23 for no good reason. They only reason I know this, besides calculating fuel mileage at the pump, is because I have a Scangauge II hooked up and set on my dash to get real time numbers for mpg, voltage, engine temperature, and intake air temperature.
 

Flounderguts

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I had an issue like this once after a rebuild on a different vehicle. After pulling out my hair, it turned out that I had the timing 180 deg from where it should be, but motor still ran because it was also a waste spark system.

Just a thought.
 

Slowestranger88

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I haven’t been able to figure it out till I had this thought. Bare with me I’m not sure how relevant of a question it is. But when installing a in-tank fuel punk, should it always be done with the tank empty? Does it make the pump read wrong?
this all started happening after I did that pump. And I’m not 100% sure. (It was about a month or two before I started this thread) but I think I installed it with 1/2 tank and it read empty. I went to town and filled it up. But at the time I was trouble shooting so much stuff trying to get it back on the road I either might’ve over looked it because it was finally running right, or I’m wrong because of how scrambled my brain was at the time trying to make sure it ran so the ol lady couldn’t say she was right about it being a hunk
 


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