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2.9 MPG Loss After Engine Removal


CrashDriver

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So I had to pull the 2.9 out of my 1988 ranger recently due to a hole in the oil pan (engine mount bracket somehow came loose, a rock got between the cradle and the pan, and then while offroading proceeded to punch a hole through the pan).

I reinstalled the engine, and noticed that now when driving I get about 14 or a tad more MPG - driving the same route before the engine shenanigans, I was getting at least 19 MPG.
I was attempting to address that and a couple other issues and ended up following a couple parts rabbit trails that I will list, in case they may or may not be related problems.

1. The first thing I noticed after install was that the engine would idle down to the proper rpm - 1,000 when cold and then down to 700 - but then it would slowly fluctuate its way down to 500-300 rpm. I found some information on adjusting the idle and did the whole sensor disconnect and idle screw and etc, and it mostly idles where I want it to now, but it still often fluctuates up and down about 50 or more from 700, and once I caught it randomly idling at 800.
I feel like something odd is going on there because before I set the screw it would still idle like normal for about 5 seconds before it would start to drop.

2. I replaced the... I think MAP sensor (has a vacuum line from plenum, sensor plug, is seated on the firewall on pass. side), to see if that would fix the idle problem. This was before I set the idle by hand, so obviously was unsuccessful - I did not notice anything change after this.

3. Also before I changed the idle, I cleaned the air bypass valve thingy as best I could that the sensor plugs into. Also no change at all.

Off the top of my head those were the replacements/repairs I did to try to solve the problem.
Also I have some other notes on things I noticed that I did to the truck or didn't seem right with the truck (but also don't know if they are related)

4. I set the timing with the light to exactly +10, the engine runs and sounds just like it used to besides its odd fluctuation. I get they don't always run steady but my gut tells me this is more than normal.

5. I had some troubles with the old plugs on the main harness when I was trying to stick everything back together. There had been some old cob-jobs on it before, and some of the big plugs were just very gummy. I believe they are all connected properly, but there's a tiny niggling in my mind that possibly something could be off- though on the other hand if something is 'off' it would probably be very off. There are also some unmarked plugs (I labelled everything I separated) that I just assume are parts of other trim packages or something since she's just the XLT. worst case if I must I can put pictures on here.

6. Before the engine incident, I had pulled the bed off so I could replace the fuel pump (the old one worked fine besides the fuel gauge was not getting the proper signal). Afterwards the gauge worked, but the new pump (Carter) I believe had issues out of the box because at halfway full the gauge would read empty (I tested it by hand before putting it in the tank and it did the same, but at that point I just assumed there would be some difference once it was submerged).
Since then I have caught a whiff of gas when I have been underneath the truck - it seems to be more rearward but I'm not sure exactly where. I have another pump (US Motorworks) coming in that I optimistically hope will fix my gauge misreading, and at that point I will take the bed off and have a better look at were the fuel smell is coming from. Which also started since the engine has been out.

7. But whatever the fuel leak is I would assume it can't be bad because I tested fuel pressure and with just the pumps it was 40psi, after startup it was around 30 psi. It seemed to hold pressure fine at the time but I also didn't let it sit very long.

8. When I was plugging the injector wires back in, a couple of the rearward plugs were able to rotate. Not sure if that is normal, and although I intend to do my research on the injection system at this point in time I have little understanding beyond the basics of its functionality.

9. Just for kicks, I tried something I've found a couple kind of skimpy articles about - the engine flush/flooded engine mode, I think it's called. turn key on, push gas to the floor, turn the engine over, and supposedly it shouldn't start unless you have an injector leak. I'm not sure if that was for different years or anything, but when I did it the engine ripped right to life without any hesitation.

10. It blows plumes of white smoke pretty much all the time- cold, hot, after I get back from a half hour drive from work, more than it used to I think. The coolant doesn't really go down either - I will fill it to the top occasionally and when I check a week later or so it's settled down to about the same level every time. Never gone low. the smoke smells of gas as far as I can tell.
 


Uncle Gump

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I would fix the fuel leak before doing much else. Then see where your mileage ends up.

Unsteady idle is usually a vacuum leak.
 

racsan

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On the vacuum leak: I dont know about the 2.9 , but the 4.0 ohv (which was developed from the 2.9) can suffer from a failed fuel rail gasket. The fuel rail (on a 4.0 ohv at least, 2.9 design may differ) is sandwiched between the upper “air horn” and the lower intake that fastens to the engine. My ‘93 4.0 had that gasket fail, had a idle issue and couldn’t find until I tore into it. I went the whole 9 yards & pulled the whole intake apart but it was apparent when I got to the fuel rail that gasket was the issue. It had pulled in at the front & rear.
 

RonD

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Change PCV Valve if you haven't changed it, should be changed or cleaned every 3 or 4 oil changes
Dirty PCV valve will cause idle issues
 

CrashDriver

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I would fix the fuel leak before doing much else. Then see where your mileage ends up.

Unsteady idle is usually a vacuum leak.
Update:
Finally had the time to replace the fuel pump (the fuel gauge reads right now with the US motorworks pump) and after running it through a tank, my mileage reads 12.8 MPG. This was after driving with the hubs locked and in 4x4 through the snow for a while back and forth from work so I would assume without that detail it would still be around the 14 mark I was at before.

Still smokes (gray) like the dickens but there is zero coolant loss.

I tested the throttle voltage to see just in case if the clear flooded engine mode start was because the TPS didn't read right, but full throttle was about 4.5+, which I read is pretty much right... I think. in Doing so I also readjusted the idle screw so at idle the voltage was exactly 1.1 volts, so now it idles kind of screwy low again. Sometimes more, sometimes less.

At this point with my little knowledge of the issue I'm figuring it must be the injectors and it's running rich, so I'll probably pull them out when I have time and clean/replace them.
 

Shran

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I believe that your TPS voltage at idle should be somewhere around 0.75v.

#8, totally normal for injectors to be able to rotate
#9, try the "zip tie mod".... zip ties on your throttle cable to take up the slack caused by a weak return spring or stretched cable. Your engine probably started during this test because your throttle was not open all the way.
#10, steam from the exhaust in the winter is normal, it is just condensation in the exhaust system. I would not worry about this at all until warmer weather, if it goes away in the summer there is no problem
 

CrashDriver

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I believe that your TPS voltage at idle should be somewhere around 0.75v.

#8, totally normal for injectors to be able to rotate
#9, try the "zip tie mod".... zip ties on your throttle cable to take up the slack caused by a weak return spring or stretched cable. Your engine probably started during this test because your throttle was not open all the way.
#10, steam from the exhaust in the winter is normal, it is just condensation in the exhaust system. I would not worry about this at all until warmer weather, if it goes away in the summer there is no problem
Thanks for the advice, I forgot to mention when I talked about the tps voltage that that was after I did the zip tie mod on the gas pedal - I also tested it just rotating the lever on the throttle body with the cable taken off and that was what gave me the 4.5ish result.
It has a brand new NTK tps sensor on it as well, but unfortunately I chucked the old one so I don't have anything to compare it to now.
 

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