Longbed 90

My 90 3vze is running rich, failing smog. I've switched out the following trying to isolate the problem...

New:
ECT Sensor
ECT Sender
TPS, properly adjusted and triple checked
VAFM
O2 Sensor (Denso)

From a donor vehicle:
All six injectors
Fuel Pressure Regulator
ECT Time Switch
EGR Valve
Catalytic Converter
Cold Start Injector

This thing has a clean TB, and a complete top end rebuild, and I can NOT for the life of me find whatever &%$ing gremlin is living under the hood!

I've measured the voltage on the Vf pin with TE1 and E1 jumped, warm engine, resulting in 4.97 constant voltage, as per some comments on a recent thread I posted.

Still running rich, slightly high idle. Truck is probably in open loop...

Can someone please tell me what to look at next?

RJR

No CEL codes, I assume. Are you sure the check engine light is working? Does it come on with key on before you engage the starter?

Your Vf measurement shows that the O2 sensor is working, and is agreeing with the emissions folks that it's running rich. Question is, why isn't the ECU doing anything about it?

Try measuring the Vf pin with TE1 open. That'll tell you what, if anything, the ECU is trying to do. If it's at 0V, you're probably in open loop.

You might have an actual faulty ECU. That's rare, but does happen. One possible scenario is that the ECU is misreading the ECT and doesn't think the engine ever warms up. Make sure you have good wiring and connectivity all the way from the ECT to the ECU.

scope103

For that matter, why don't you just unplug the ECT? That SHOULD throw code 22. If not, check to make sure you've got a valid CEL (on solid with key-on, engine-off, flashing 2 hz with TE1-E1 shorted.)

Longbed 90

No CEL codes. I pray for one, as at least it gives me a direction in which to go. Light works, comes on with starter. It also threw a 71 at me like clockwork when I forgot to connect the EGR temp sensor wire after I swapped the valve.

TE1 open? Is that "unjumped"? No wire connecting it to anything?

And the open loop... this is the thing I think I'm facing. Is there a source either you or Scope knows about that lists every single component that would cause the vehicle to stay in open loop? What, in other words, are all of the devices that signal the vehicle to run in closed loop? I'll check the wiring first. I'm assuming all there is to it is:

A) Wiring exists
B) Wiring is undamaged
C) Wiring is conducting current

How much of a PITA am I looking at there?

Scope, if I understand correctly, the ECT sensor is the one I want, and it is the blue one, no?

As I understand:
Red is ECT switch for EFI
Green is cold start time switch
Purple is ECT temp sender

RJR

TE1 "open" is indeed "unjumped" - no connection. Just like it came from the factory.


If you want to get more insight on what the ECU thinks the sensors are doing, there's always the program I wrote and published here about 18 months ago that reads the serial data stream from the diag port. That will tell you what the ECU is measuring for all of the various sensors, and how it is responding. A bit of electronics work to get the port connected to the computer properly, but probably less time than you've spent already. Not sure it works on a '90, however.


You can download the archive file from this thread. https://www.yotatech.com/forums/f116...reader-278801/ . Look for the attachment "ToyotaDiagRelease.zip" in the first post.

scope103

Well, it's hard for me to tell. The Water Bypass is surprisingly non-standard (for instance, I have an extra sensor because I have both 4wd and an auto). So I've included what SHOULD be the wire colors (note that many of these have an extra cover over the wire; you'll need to pull that back to get the wire color). At a minimum, the ECT and the CSI Time switch are both 2-wire, the gauge and AutoTrans sensors are single wire.

Longbed 90

Yeah, I've found that to be painfully true. My donor vehicle is a '92 AT, and it's a differently configured bypass unit altogether. Toyota routed the heater hose down through that rather than through the underside of the plenum.

Thanks for the wire colors. I suppose I should have been more specific that I was referring to arrow colors in the pic I linked.

Either way, thanks again for the help. I just don't know what else to test at this point. I'll run the test RJR mentioned with TE1 open, but do either of you know what else would signal the ECU to remain in open loop? I'm stuck there.

Janos01

It is possible that you have a bad injector from the donor car, where it is leaking or spraying too much fuel. How is your MPG on average? I would recommend giving the throttle body a good cleaning Also have you tried replacing these as well?:

Spark plugs
cables
cap & rotor - a bad cap will cause a weak spark and may contribute to the engine running rich.

Longbed 90

Yeah. Sorry, forgot to list those. I just put in new plugs and wires. Cap and rotor were done within the last 15 months, but I can try that again.

I'll pull all the plugs, double check the gapping, and see if one cylinder is running rich. It's possible that I do have a bad injector from the donor. How else besides a fouled plug can I diagnose that?

TB is clean, and I just blew out the TB coolant bypass with air yesterday, as I had stumbled upon someone with my exact idle issue that had a blockage there. No such luck for me.

I'm getting 12mpg perfectly, every fill up. No matter how I drive.

Janos01

Sound good man, even when it is running well the MPG is not much better. I just replaced my cap, rotor, wires and plugs this past Sunday. My 90 4runner was running a bit rich and idling a tad rough. Turned out I had 4 out of 6 contacts broken under my distributor cap and only 2 plugs out of 6 had char on them, the rest were clean. Had my whole engine rebuilt due to a blown head gasket and once again the shop that did it is still causing me hell for little issues they did not take care of. Otherwise let us know whats going on and well help as best we can.

scope103

I'm grasping at straws here, but I wonder if you have an open in the O2 sensor (not heater) circuit. According to this Toyota article http://www.cygnusx1.net/Media/Supra/...taTech/h44.pdf, failure to enter closed loop can be caused by engine too cold (you've explored that) or lack of response from the O2 sensor. (This is an OBD-II vintage article; it does note that a missing O2 sensor signal should set an OBD-II code. )

So ... I would check the O2 sensor output directly at the Ox1 port. VF1 is conditioned Ox1 (so it flops from about 0 to about 5v), Ox1 is straight from the sensor so it flops from about 0.1 to about 0.9v. You'll need a voltmeter with a 2.000 volt scale; most cheap digitals have that.

The other suggestions for causes of running rich are all fine, but the ECU really should throw code 26. That why I think Longbed_90 may be on the right track re open loop.

Longbed 90

Well, I have to solve the issue of it not passing smog, so the rich condition (which is undoubtedly causing the poor fuel economy) has to go. Aside from that, I was able to pull 18 MPG out of the rig before all went to hell under the hood, even with 31s on it.

I just dropped a new cap and rotor on today, and ran with a disconnected cold start injector wire.

There seemed to be an immediate improvement.

Scope, Here's my thinking on that:

Cold start, idle adjust screw bottomed out, my rig was running ~800 RPM Just about right, but it would search a little once it warmed up a bit at a stop light.

At hot, she ran about 1100 RPM, with still some searching. There was also a hesitation-ish bog down between 2k-3k RPM, but not enough to notice unless paying close attention.

Anyway, seems logical to me that a constantly leaking cold start injector might cause the idle issue AND rich issue. No?

What part of either issue could be caused by a worn distributor cap/rotor?

Gonna drive it some more and see what goes on, but I will most likely be replacing the O2 sensor a bit down the road anyway, just due to it being slightly over spec as we talked about before. Gonna run your test you mentioned first. I'll get back to you...

Oh, also... I did pull the plug on the ECT sensor, and it triggered an immediate CEL with a 22 attached. ECU seems good at least that far.

Longbed 90

Cap and rotor did not solve the issue. Nor did removing the CSI plug.

I'm ready to find a shaman to perform an exorcism. I'm even considering something more drastic: taking it to the stealership for a diagnosis.

AKHeathen

O2 sensor. if it's running rich and the ecu doesn't think so, it would only be logical. It's one of those 150k+ tune-up items.

Janos01

If all those did not fix it, it could be a bad O2 sensor or a leaky injector causing this.

Longbed 90

Sure enough, but the O2 is a year old, and I'm stumbling over this:

How would a brand new Denso O2 cause a rich condition enough to ruin itself?

And how do I diagnose a leaky injector?

I'm just tired of throwing parts at it.

Longbed 90

For sure. I've already done it twice. Once two years ago, I used a universal (knowing no better) that went out in a few thousand miles, throwing a 25 and a 26. Put in a Denso, cleared it right up.

That was a year ago, if I remember correctly. I haven't put but maybe 3500 miles since then... maybe.

So, could a bad head gasket, bad cat or other bad sensors have caused the rich condition that shot my MPG and then in turn ruined the new O2? I suppose it's worth the sixty bucks to find out.

Longbed 90

Just put in a new Denso O2 yesterday. Idle issue still remains, doesn't seem to be much difference in rich issue. Still smells the same. We'll see after a quarter tank...

SO flipping frustrating. Now what? Anyone?

AKHeathen

pull your battery cables and tape together fo about half an hour, then reconnect. it should be reset to new values and learn. if it's fixed, it should run right.

Longbed 90

Will do. Tape together? As in, just keeping them from touching anything else, or tape terminals in contact with one another?