Been finding this site useful for quite some time, and finally surfaced with question...

I have a 95.5 Taco, 3.4 liter with 191k miles, every last one of them mine. It's in pretty decent shape, but recently I began experiencing a hesitation (feels like a misfire) at RPM ranges above idle. Idle feels OK. It eventually popped the CEL, and I put a laptop OBDII scanner on it. Code P0303, misfire in cylinder 3.

I reset the CEL and pulled the plug on cylinder 3. Looked in good shape, changed out not long ago, so I thought maybe the coil pack. I swapped the clylider 3 and 5 coil packs and took it out for a drive. Still hesitated and the CEL was back. Still P0303, so it wasn't the coil pack.

At this point I'm thinking either a bad electrical connection to the #3 injector, or a cruddy injector. I see CVU brand injectors going for in the $70 each range, or maybe $160 for a set of 6 (odd, but good pricing). If I'm going to the trouble of getting at the injectors, the marginal cost to do all 6 doesn't seem too great.

I am aware of the injector cleaning services that will do it for about $15 per, but that's not an option for me. I can't afford the have the truck down for the amount of time it takes to ship the injectors back and forth, otherwise I'd do that.

So, first two questions....

1. Are CVU injectors decent quality?
2. Do they come with the O rings/grommets or do I have to get those separately/extra?

Now as to fuel trim....while I had the OBD scanner going, I noticed the B1S2 O2 sensor fuel trim stayed pegged at 99%. That seems odd. The B1S1 O2 fuel trim generally moved around in relation to throttle changes.

The voltages for the S1 and S2 Oxygen sensors exhibited similar tendencies. The S1 voltage gave a nice sine wave, but the S2 voltage did not. They seemed to flip between maybe 0.1 volts and 0.7 volts, but very slowly. That is, it would stay at a low voltage. for quite a while, then flip up to .7 volts and hang there for some time. That can't be right. It's my understanding the S2 Oxygen voltages should somewhat track the S1 voltages, but at a diminished rate.

Last question...

3. Bad post-Cat Oxygen sensor?

I don't see these as necessarily being connected, so maybe I'm just "lucky" to have two unrelated things happen. OTOH, could the ECU be doing something to the engine in response to the S2 feedback that causes a marginal cylinder 3 to misfire?? I guess that was question 4.

Any assistance (or even rude remarks) would be appreciated!

 

The next thing I would do is a compression check. If a cylinder has a mechanical problem that is bad enough the ECU can report that as a missfire.

Do not look at the fuel trim values for B1S2 sensor. There are no trimming functions on that sensor and the scan tool might just be defaulting to a max value.

Gadget

 

Compression testing is a good idea and the only one I haven't done. I'm not sure the unit I have can reach down into the well. An excuse for a new tool!! However, I don 't think a valve problem is likely, as the missing has come and gone on several occasions. But I do need some sort of long rech compression tester.

I've done all the electrical tests on power to the injector, including putting an oscilloscope on the signals to the injector (an oscilloscope in the garage is a magical thing...). All OK.

Rather than buying a set of non-OEM "remanufactured" injectors, I found a set of 6 Toyota injectors for a 3.4 engine for $10 each on eBay. Witchhunter Performance will clean and test them for $15 each, so I will have a full set of 6 Toyota injectors for $25 each or $150 for all six.

So the truck stays running until I have all the finalized, purdy injectors in hand.

Still haven't made a lot of sense of the rear Oxygen fuel trim signals, but the sensor tested OK electrically.

 

One of the best deals going is the compression tester from Sears. The hose will fit down the spark plug tube just fine and screw into the spark plug hole. It will hold the pressure until you release it.

I would not spend any money on injectors until you do this test. I would not drive it until you do the compression test.

If you have a valve that is not closing, can can destroy it by causing it to over heat if you continue to drive it. The way valves like the exhaust valves are cooled is when they close against the seat and transmit the heat into the head.

Gadget

 

Hmmmm...Good advice. I guess it's off to Sears this evening to add to the tool collection. Thanks!

 

Your injectors are probably dirty. As long as your tune-up is good, then most likely it is a clogged injector. Also the computer could not be grounding out the negative side of a coil. You have to verify if you are loosing spark, fuel or compression. We can most likely rule out spark but you still don't know if that coil is getting grounded out by the computer. Fuel your probably can't tell without a fuel gauge and an injector pulse tester. Compress you also need a gauge.

The oxygen sensors your reading wrong for the most part. You have three sensors, B1S1, B2S1 and B1S2. Ignore B1S2. Bank 1 sensor 2 is only there to monitor catalytic convertor effeciency and it has nothing to do with driveability. It's only job is to make sure you cats are working. That O2 WILL not toggle like the upstream O2's. If it mimics the upper O2's, you either have a worn out cat or a bad downstream O2 but again this does not cause a driveability problem.

You need to do the basics first but you lack some of the tools. DO NOT use a regular test light to test injector pulse or coil pulse. This can damage your computer. You need to get a circuit safe test light preferably a LED test light.

From my experience it is most likely a injector problem. You can do an ohm reading and that right there can tell you if you have a bad injector. Just because an ohm reading is within specs, injectors can fail under load.

Good luck!

James

 

Uh oh...While I would dearly love it to be a dirty injector, I did a compression test (engine cool, I know, not quite the proper way) and found cylinder 3 was running about 15 or maybe 20 psi less than the adjacent cylinders 1 and 5. That doesn't give me the warm and fuzzies. Seems odd that it wouldn't be lower if it were a bad valve though.

At this point I think I need to bring it into the shop guy I trust and have him do the diagnosis. I personally draw the line at pulling the head of 6 cylinder Toyota engines. Old 4 cylinders, OK. New 6 cylinders, I pay people to deal with those headaches.

I seem to recall that pulling the head (which I assume has to be done to deal with a valve) starts the dollar clock at at least $800. And once in, it would only make sense to deal with anything that remotely needs attention (yeah, them fuel injectors too), so $1.5k to $2k doesn't seem extraordinary. I have to consider if it's worth it on a truck with 191k miles. The new Tacomas look pretty sweet.

As to the oxygen sensors, I think my 95.5 only has two, a B1S1 and a B1S2. I don't think there is a Bank 2 to this vehicle. And since you said I could ignore sensor B1S2, that sounds like good advice. However unfortunately I don't think that's my problem.

Thanks for the assist.

Tom

 

Tom, without knowing what the compression is on your other cylinders, I have no way to identify how bad it really is. If your only getting 10-15 lbs difference you have nothing to worry about. Also you have to factor in other things as well, was the engine up to temp, did you have all other spark plugs out or did you leave the throttle fully open when you did the test, things like that.

I'am trying to save you some money by you doing that basics or whatever you can do with the knowledge and tools that you have. I still think it is an injector. If you feel you do not want to handle it, then by all means bring it to someone that is qualified. Make sure they do the basics as well. Any good technician should be able to diagnose this problem in about an hours time for the most part. Don't feel that it is something worse than it actually is. These 3.4's when maintained, usually don't need any mechanical part and it usually comes down to something electrical. That has been my experience over the years working on most Toyota products. Good luck and keep us posted.

James

 

Interesting discussion with my serious car guy (I only show up at his shop with my truck with ugly things...Easy things I do myself). I've always found him quite straight and I know he's talked me out of doing more work than I've actually had him do.

Anyway, I had my truck in there about three months ago because it was missing (sound familiar?). They found a bad plug in the good ol' number three cylinder. I couldn't remember which cylinder it was until he checked his records today. They did a lot of checking at the time in an attempt to determine why a fairly new plug went bad, including a "block check" where they sniff the coolant for hydrocarbons to see if there's a leak. It was negative and their testing was inconclusive.

So three months later similar symptoms now appear. Based upon our rather lenghty discussion and his experience with that type engine, he felt there was a 90% chance I have either a slight leak in the head gasket or a small crack in the head. He feels the lower compression reading in the #3 cylinder could be caused by excess gas washing away the oil seal on the cyclinder wall. I have a slight roughness when starting, which rapidly goes away, consistent with a very small amount of coolant in the cylinder. The kicker is that I've noticed my coolant level in the overflow container has been slowly going down (very slowly). So, maybe. He's made good calls in the past.

Now the killer...He pulled records for similar work he's done on 3.4 engines over the past couple of years (and he's seen more than a few with cracked heads and blown gaskets), and the bills started at $5k for the work! Granted this may be a higher price (he's not a dealer but specializes in Toyotas, is first-rate and only uses Toyota parts), but it's still breathtaking. His advice to me was to NOT do the work, but to trade it in toward a new Tacoma while it was still working. But looking up the value, I see it would only be a thousand or less.

And here's the weirdness...Last night I pulled the #1, #3, and #5 plugs to do the compression testing. Did my measuring and put everything back as found. Today, the engine has been running smooth! I can't say it's 100%, as there may be a little roughness, but there's no lurching or clear misfiring. Now THAT should not be happening! If it's a leak, and small enough, I suppose it could come and go, but it seems farfetched.

As I have some injectors on the way to me, I'm inclined to switch out at least the #3 one and see what happens. I have nothing to lose in that arena. If it's indeed a failing gasket or cracked head, then perhaps the truck is terminal, and I'll drive it until it dies. Could be a few weeks or maybe a few months. The downside is that while it might be decent local transportation, I don't think I'd like to be out in the boonies with it. And that's sort of the point of having a 4WD Tacoma, isn't it?

Tom

 

What color was the tip on #3 spark plug? It could be a head gasket as well. This mechanic should do a cylinder leakage test after everything I said is verified.

James

 

James:

My mechanic thinks it's either a leaking head gasket or cracked head, very small in either case. The number three plug tip didn't have any discoloration that I could see. It looked in very good condition, as it was only 3 months old. I did note that it was "squeaky" and stiff when I was unthreading out of the head. I just attributed to a lack of antisieze compound, but now I'm not so sure.

My mechanic did a leakdown test three months ago, and it turned out OK. It was what I call my "$200 spark plug". $5 for the plug and $195 for all the diagnostics to determine it was only a plug. A bad plug was rarely seen by them, so they did a lot of tests to see if it was something else that caused the plug failure. The tests came back negative, so they were forced to conclude it was just a freaky bad plug. Now their thinking is that small amounts of coolant in the cylinder could have caused the plug to fail. What's still not clear to them is why their testing didn't turn up an obvious leak. And what's not clear to me was how my diddling with the plugs last night could have made the problem go away, at least for the moment. I do believe it's a full moon right now, so maybe that's it.

Tom

 

one other cheap item would be to replace the spark plug (with a factory plug). As I read it, you replaced your plugs not long before the stumble began happening. 2) the stumble happens just above idle.

I experienced a stumble at 1300 rpm or so. It came after replacing the stock plugs (original with truck) with some cheap autolites. a year or two later I went back to factory plugs and the stumble went away. Whether it was a single electrode vs dual electrode issue, or quality of a 1$ plug vs a 10$ plug, or simply a mis-install on my part remains unknown.

Like I say - its a low dollar attempt. Though if your stumble is still gone it may lend some credence to operator error on my part (of the autolite plug).