briholt

Fsm says that the ECu has a wire called "HT", which is for the heater on the o2 sensor.

Should I be able to test resistance/continuity by connecting the ohm meter to the ht on the female plug of the o2 sensor (by the cat converter) and the ECu ht wire? Wouldn't that let me test continuity?

Likewise, could I do that with the Ox wire on the ECu and one of the wires of the o2 plug?

scope103

Sure, if what you are trying to do is check continuity of the wire from the ecu to the sensor, as contrasted with testing the continuity of the heater in the sensor.

There are no components between the sensor and the ECU to interfere with your plan.

briholt

Exactly. I've followed 4crawlers tps instructions and they came to specs. I've got a new o2 sensor, too. Still get 13mpg.

So I would like to look for shorts.

scope103

If there is a short or open in the heater circuit that should throw code 21. An open or short in the Ox circuit should throw 25 or 26.

If you really want to check the Ox circuit you can check the voltage on the Ox pin of the diagnostic connector. About 0.3 to 0.9v, flopping back and forth 8 times in 10 seconds. Or ground TE1; with the throttle open VF1 is "conditioned" Ox1, meaning it flops from 0 to 5v instead of the actual sensor voltage.

Even more fun is looking for the learned Air/Fuel value. The voltage on VF1 has 5 voltage steps from 0 to 5v. 2.5v is "normal," with less than 2.5v meaning the ecu is decreasing fuel.

briholt

So, yeah, the bigger problem for me is that this ecu never throws codes.

I get crap mpg, just passed my emissions test with the state, seems to run fine with no hesitation, stalling, etc, truck won't run without being hooked up to the ECu, but I get crap mpg.

So maybe the ECu is out?

Otherwise, maybe I've got mechanical drag of some kind? My big hypotheses for that will be something in the tranny, or rear axle. I've already checked the brakes, and I've put new front bearings in, so I think those are okay. Could be wrong.


I really appreciate your comments btw, delving into the efi of a 22re is new for me. I thought it would be easier than my old 22 r, but this one is stumping me. So I have some clarifying questions below.

So I'm clear, where is this pin of the diagnostic connector? This phrase makes me think under the hood, not the ECu... The place for the "special tool" to obtain the codes.

"Ground TE1" is not a phrase I've seen. I've seen "E1", though. Is E1 a ground?

Also, would I need the engine running to check with the throttle open, or would having ignition on be enough?


"Learned"? Could that be a typo for "lean"?

And "decreasing fuel", what does that mean...that the ECu is detecting low air intake and thus reduces the fuel into the fuel mix?

Again, thanks for listening to my questions.

scope103

Yes, the diagnostic connector is where you always start. In addition to E1 and TE1, it has about 16 other connections, all labelled under the cap.

E1 is "a" ground, so to ground a terminal means to connect it to ground. E1 is the most convenient; just push a piece of wire into E1 and TE1, then measure the voltage from Ox (or Ox1 if you have a California truck) to "ground." (again, E1 is convenient).

What signal do you get from the O2 sensor when the truck is not running? None (0v). The sensor has to heat up to about 700°F to start working. So yes, the truck has to be running, and warmed up.

If the O2 sensor doesn't work until the truck is warmed up, how does the ECU know how much fuel to add for any given throttle position (actually, VAF value)? The ECU uses the fuel trim it used the last time the O2 sensor was working, because it learned the required fuel trim. (There's a value set at the factory which works most of the time on a new truck, which is represented by a fuel trim of 2.5v. But if you have a fuel pressure regulator running a little high or have a slight vacuum leak, the truck trims the fuel mixture to match. And it's smart enough to "learn" the adjusted trim!)

If your fuel trim is all the way to one side, it means that something is slightly wrong (e.g., vacuum leak) and the truck is trying to make it work. If things get out of the range where it can trim it out, the ECU throws a code.

More detail: http://www.autoshop101.com/forms/h27.pdf

briholt

In pretty sure I've got no vacuum leaks, at least none that are sensitive to starter spray.

It's posts like yours that remind me how much a bear these efi's are. Lots of insider knowledge that takes much practice to pick up.

Thanks again for your help and resources.

scope103

It's not insider knowledge if it's in the FSM. If you're not using the FSM, well ...

If you'd ever went through a true overhaul of a carburetor, you'd thank your stars for EFI. Lots of "bend this rod a little" and "get the angle of this to 18 degrees." The only reason people ever accepted carburetors was a) that's all there was, and b) older engines would still run (albeit crappily and with awful mileage) with the carburetor way off.

briholt

Sorry to disagree, but the fsm isn't perfectly helpful like it is with mechanical instructions. It's why 4crawlers's site is frequently referenced, for example. Yes the information is all there, but it assumes background knowledge that I don't have.

I've rebuilt a 22r, and probably could a 22re, but the ECu part isn't intuitive. It is what it is, and is better than the older carbs, but like today's newer cars, requires more understanding about circuits than I have. Or for that matter, the previous owner who couldn't make it work, either, despite his small business of rebuilding Mitsubishi engines.

briholt

Hey checked the o2 sensor and it appears to be working fine. About 1 fluctuation per second while at 2500 Rpms.

I haven't get read the auto 101 resource, but what would be a culprit for poor gas mileage if not the o2 sensor.

scope103

There are about 1,000 possibilities, starting with a "lead foot." (My truck's mileage is very sensitive to driving faster than 60mph.) But from a diagnostic standpoint the first place I'd look is compression.

briholt

Yeah, I won't bother with you regarding all the possibilities. This is about where I remember why I never fix this truck---too many things to rule out.

It's not a lead foot (I don't drive fast, never have, and my last truck 22r got about 22mpg). I could check compression but the engine only has about 70k on it. Seems sensible to check though. The plugs look normal, never fouled, but it's been a few miles since I've checked.