Lets talk tune ups and MPG

I recently purchased a 84 2wd auto van with 223k on it. I have driven it about 400 miles so far with very poor MPG, Almost drained the full tank after driving around 200 miles.

First problem I fixed was to replace the t stat and I am hoping that helps. I do have a CEL on that I need to track down, but since its missing the coolant overflow tank, Cat and the PS pump i figured it might be for one of those. But I need to check it anyway.


Is there anything else to look for other than the plugs and wires? Do I need to change the dizzy cap on it also?

1st thing to do is CHECK CODES. 2 common issues that cause poor MPGs are a failed TPS (Throttle Position Sensor) & a bad O2 sensor. The codes should help confirm which one (could very well be both). There are multiple threads here that deal with both, so once you know what it is do a site search for more info.

There are different levels of tune-up. The most comprehensive one is done at 60k mile intervals. If you don't know when the last 60k mile tune-up was performed, especially if there's issues, you should do the most comprehensive one. Spark plugs can be pulled, inspected, & possibly put back into service, but I would recommend replacement. When it comes to tune-up parts I'm a stickler for genuine Toyota or OE equivalent. Factory plugs for the 4y were Denso Platinum P16R (not sure about the 3y). These are a 60k mile plugs. Toyota will want around $15 a piece, but they can be had at www.RockAuto.com for under $5 each. The rotor is inexpensive so just replace that. I will often replace dist cap & plug wires "just because" but these are expensive (at least from Toyota). These parts however (if OEM) can last for a very, very long time. So if money is an issue then I might let these slide. If they are aftermarket I would just replace. If you decide to re-use, inspect the inside of the distributor cap & scrape any excess carbon from the rotor contact points. These contacts should be reasonably flat (top to bottom). If there is a noticeable groove in any of the contacts replace the cap. The PCV valve near the back of the valve cover should be replaced. This can be a PITA because it's likely the mounting grommet & hose will break. Any time I do a PCV valve on an old neglected van, I automatically plan on replacing the grommet, all formed vacuum hoses in the area, and the valve cover gasket. The last one I did also required the power steering return hose as that one broke off when I tried to move it out of the way :no:. I do the valve cover gasket because 1. It probably needs it & 2. If the PCV grommet breaks (and it almost certainly will), you will need to fish out the hard rubber chunks from inside the valve cover. That's just easier to do with the valve cover off.

The fuel filter & air filter should also be included with the tune-up. I like OE Toyota filters too, but not as picky about aftermarket parts here. If you determine the TPS is shot, then now is a good time to REMOVE & CLEAN THE THROTTLE BODY. There is a video at the end of that thread giving details on how to set up your new TPS. Timing should also be checked and adjusted (if required). 3y & 4y engines are different in this regard. Since you have the 3y, you will need to disconnect the vacuum advance diaphragm from the distributor and plug the vacuum line. Then check/set the timing. After timing is verified you should then re-attach vacuum line and check again. If the vacuum advance is working correctly you should see the timing move when the diaphragm is hooked up. I have very little experience with the 3y engines, but I believe the timing set point for these is 8 deg BTDC. If you don't already have a factory service manual you should get one as I could be wrong on the procedure and/or the timing set point. I probably forgot something, but this is most of it. Good luck & have fun! Tim

I just had to replace the battery due to all the dash lights coming on. I assumed it was the alternator and had it tested and it passed. The battery even though it was less than a year old had a dead cell.

I replaced the battery with a new one and still have my dash lit up. Check the fuseable links next?

Check the small wires that go into the back of the alternator too. Over time they fracture and break inside the insulation (right where they go into the round plastic plug).

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Originally Posted by timsrv

Check the small wires that go into the back of the alternator too. Over time they fracture and break inside the insulation (right where they go into the round plastic plug).

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Well the new batter died on me yesterday in less than a day. Left the moonroof open for the rain. The insolation on harness was tough like most of the harness but I didnt see any cranks in it near the plug.

I guess I need to get a volt meeter and see what its getting at the battery since alt bench tested okay.

Make sure that you aren't leaking any power steering fluid. Lift the seat & turn the wheel to see if it's squirting out any of the power steering pump seals.

Otherwise, disconnect the cables from the battery clamps & clean the ends of the cables & clamps if there is any green corrosion.

What voltage are you measuring at the battery when the van is running?

I don't know where you had the alternator tested but chances are it's probably on it's way out.

Well it was 12.2 at the bat while running with a new battery. Dash lights are still on.


For the record I do not have power steering. But im sure plenty of fluid has been spilled on it.

I'm not 100% sure, but I think it should be 14v even at idle. I know mine does put out 14v at idle, but I'm not assuming this is normal. If you rev it up then it had better be 14v then atleast.

The range I look for is 13.5V - 15V. I like seeing it about in the middle of that range, but anywhere inside is okay. Keep in mind a fully charged battery is 12.66V at rest. Anything under 13V is not enough to charge (at least not effectively). Anything over 15V can cause battery overheating and/or other serious issues. Tim

Yeah, seems like there might be a bad diode in the alternator.

However, I don't think the voltage at the battery should read 14V all the time if the battery is fully charged. I was under the impression that the alternator shouldn't be working that hard all the time.

Keep in mind the battery's "state of charge" is what determines charge rate. At 14V a mostly dead grp 24 battery will pull around 30A. As it charges the internal resistance changes resulting in a lower charge rate. A typical scenario would be as follows: 1st 30 min. ~30A, 30 - 45 min. ~ 20A, 45 - 60 min. ~15A. As the battery approaches full charge the rate of charge will drop to almost nothing. Even at 14V a fully charged battery will only pull around 2 or 3 amps. 15V would be too "hot" if you were to run the engine 24/7 but in automotive applications that typically doesn't happen. Most drivers will run the engine for less than 2 hrs a day at less than 30 minutes intervals.

Cusco, the problem you are describing is typically due to a failed alternator (probably brushes). I'm a bit curious as to who tested your alternator and how qualified they were. I wouldn't put a lot of faith in a parts counter guy as they can lack the training required to give accurate results. An auto electric shop would be a better choice for such a test. Your problem can also be caused by damage to the small wires that go into the back of the alternator. These can be hard to check as bad ones will often pass a visual inspection. Over time the wire strands inside the insulation can fracture & break. Based on what you said I don't think a fusible link has blown, but I would certainly recommend checking these for any obvious damage. Here's a thread where this is discussed: http://www.toyotavantech.com/forum/s...le-link-thread

Thanks. I inspected the alternator harness and it was brittle but not cracking. For the test they just hooked it up on some sort of bench tester. With the trouble I put the alt through and the fact its a questionable to start with all hint that I should replace it anyway. I have a feeling that its on its way out already and I would rather swap it now that try and figure it out on the side of the road.

:silvervan:

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Originally Posted by timsrv

Keep in mind the battery's "state of charge" is what determines charge rate. At 14V a mostly dead grp 24 battery will pull around 30A. As it charges the internal resistance changes resulting in a lower charge rate. A typical scenario would be as follows: 1st 30 min. ~30A, 30 - 45 min. ~ 20A, 45 - 60 min. ~15A. As the battery approaches full charge the rate of charge will drop to almost nothing. Even at 14V a fully charged battery will only pull around 2 or 3 amps. 15V would be too "hot" if you were to run the engine 24/7 but in automotive applications that typically doesn't happen. Most drivers will run the engine for less than 2 hrs a day at less than 30 minutes intervals.

Cusco, the problem you are describing is typically due to a failed alternator (probably brushes). I'm a bit curious as to who tested your alternator and how qualified they were. I wouldn't put a lot of faith in a parts counter guy as they can lack the training required to give accurate results. An auto electric shop would be a better choice for such a test. Your problem can also be caused by damage to the small wires that go into the back of the alternator. These can be hard to check as bad ones will often pass a visual inspection. Over time the wire strands inside the insulation can fracture & break. Based on what you said I don't think a fusible link has blown, but I would certainly recommend checking these for any obvious damage. Here's a thread where this is discussed: http://www.toyotavantech.com/forum/s...le-link-thread

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Well I had a little spare time to look at the van again today since Im getting ready to put a alternator in it. I went to do the "Diode" test by unhooking the wires at the 10mm bolt, and bam. No spark.


Also no voltage since the battery was dead. So I would assume bad diode.

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Originally Posted by cusco-awd

Well I had a little spare time to look at the van again today since Im getting ready to put a alternator in it. I went to do the "Diode" test by unhooking the wires at the 10mm bolt, and bam. No spark.


Also no voltage since the battery was dead. So I would assume bad diode.

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Alternator swapped and running fine.

:dance2:

That's awesome!

For what it's worth, that test I talked about (touching the wires in the "plus box"), you need to have a charged (or at least a partially charged) battery for it to work. If the battery is dead, it won't spark even if you have a shorted diode. Tim

Thanks, Thats what I was thinking. But I just blindly guessed that since the battery was fully charged, the alt could be the only thing draining it.

I also managed to find 4 good matching used tires in a proper size for a good deal also. Next up is starter and brakes.

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Originally Posted by timsrv

:dance2:

That's awesome!

For what it's worth, that test I talked about (touching the wires in the "plus box"), you need to have a charged (or at least a partially charged) battery for it to work. If the battery is dead, it won't spark even if you have a shorted diode. Tim

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