Erik Beeman

1992 22RE, brand new motor, ~500 miles.



There is a weird, funky, sputter problem. It's hard to explain, but I will try my best.

It seems that it does a quick sputter, but it does it in a set pattern. What I mean, is that it does once, then approximately 10 seconds later, does it again, and then 10 seconds later, it does it again, then 10 seconds later...etc. But what I have noticed is that it does it more at freeway speeds, I usually cruise around 80MPH. It stumbles, then goes. The hesitation lasts maybe one second, then back to normal. It SEEMS, but I don't know for sure, that it gets worse when it's colder out. I have noticed this because I drive late at night, when it's cooler out. It also does it ONLY when I'm EASY on the gas, or cruising at a set speed. It does NOT stumble when I'm full throttle, doesn't stumble when hard on the gas, or doesn't stumble when decelerating. I thought that it may be that I didn't have the knock sensor hooked up, but further investigation says that this truck does not utilize a knock sensor.

Does anybody have any ideas what this could be?

TinMan

Check the TPS and AFM

abecedarian

What is the temperature rating on the thermostat? If it's too cold, the ECU may be entering and leaving closed loop mode as the engine warms and cools (thermostat closes and opens, respectively).
Has the O2 sensor(s) been checked? (Probably, but worth asking).
Have you tweaked the AFM any to richen the mixture (to accomodate your recent engine work)?

Erik Beeman

The thermostat was replaced at time of build with a quality factory Toyota, which I believe is a 180* thermostat. I do not believe this is the problem, because the sputtering happens so often I don't think it's a temperature thing (it couldn't change temps that fast).


The O2 sensors were checked very quickly by eye ball during rebuild, no testing tho. I have not messed with the AFM at all, and I am not quite sure how to do that, although I am willing to tackle anything. I do have a tach and a AEM Uego wideband that I still need to install, and this will tell me my RPMS and AFR's, so I will be able to at least see what it's doing when it sputters.

I DID do a TPS sweep, and it has a flat spot around 1/4 throttle where it hesitates (in volts). It does not move smoothly throughout the throttle movement, but I canceled a faulty TPS out because where it's rough on the sweep is at a totally different spot on the throttle than where the sputter is.


What exactly should I do to test TPS and AFM? Thanks for the help guys.

Erik Beeman

Here is a 5 minute video of the AEM UEGO, with me talking, too. Please take soem time to watch it, and hopefully we can gather some information off of it. Please ignore my squeaky girly voice.

Erik Beeman

C'mon guys, no suggestions?!?

Erik Beeman

Let's start with the basics.

It happens in a set pattern.
It happens worse when cold.
It happens only easy on the throttle.
It happens when cruising speeds.
It happens worse after I get hard on it or get the truck sideways.

I now noticed that this morning the idle jumped around, then dropped, then jumped, then dropped, then jumped, then dropped.

I think a faulty ECU? But lets check the easy stuff first. Should I check the cat? Maybe it's clogged? How do I bench test the O2 sensor? Maybe thats bad?


I checked timing today, and have it set @ 7* advance at idle. Is this ok?

Lumpy

Are you sure the AFM is not sticking??? How about this, does it do this at a lower speed but at the same RPM? Are you sure you don't have a slight vacuum leak? Who installed the motor?

Lumpy

Here is an easy way to test the O2 sensor.
[YOUTUBE]http://www.youtube.com/watch?v=XQ9vtD_ssjg[/YOUTUBE]

Timing should be set closer to 5 and be sure you have the diag jumped as well.

.

nygaard208

cap and rotor new also? just throwing that out there to try and help?

Erik Beeman

I am not sure the AFM is not sticking. I didn't even know it could. I doubt it, but I can check. And YES, it does the sputter at lower speeds, the most noticable is in second gear around 3k (just guess, I don't have a tach set up yet). It happens at the same RPM in every gear, and when it's happening on the freeway, around 80mph, I'm guessing is because it's at the same RPM.

There are no vacuum leaks. I installed the motor, and did the build. Everything is done by me, which means there is a possibility that it's not perfect. But I am very confident in my work, and I am almost 100% positive that this is not a mechanical problem.

Diagnostics were jumped when I set the timing earlier, I was around 10*, and I knew it was off so I backed it down to 7*. This made no effect on the sputtering. I don't think it's a timing issue.

Oh, and thanks for the link to the video. I will bench test it when I have time.


Cap and rotor are not new, but all points were inspected and sanded (cleaned) before install.

Erik Beeman

I forgot to mention that all fuel filters are new, including the pick-up screen that sits in the tank. Lines were flushed, and fresh fuel is being used.

Lumpy

You know you are making this difficult on us...I'm running out of ideas.

Is this a crate motor or did you rebuild? Could some of the vacuum lines be plugged around the TB that would cause this? I don't think it would be the cat...What about a weak fuel pump...My LS would cut out about 4k on a hard acceleration. The pump could not keep up but if I kept it running at a lower RPM it was alright.

Erik Beeman

The motor is a fresh rebuild, has around 550 miles now. It's not the fuel pump, because I can take the motor all the way to red line with no problems. Like I've mentioned, it doesnt even sputter at all when I'm HARD on the gas. It's only cruising and rolling on the gas. I can mash it and it'll pick up and go. I don't think it's a fuel delivery problem.

I did a TPS sweep with the multimeter. There was a flat spot, but I ruled out a faulty TPS because the flat spot was not the same throttle position as the sputtering. I very well could be wrong, tho.

abecedarian

It doesn't happen at aggressive to wide open throttle up to red-line so I'd rule out injectors and the AFM, and most of the ignition system. This points towards an issue with closed-loop mode. It mimicks what one would see with a vacuum leak- changing of the air/fuel mixture over time affecting engine speed or timing. Since there's no vacuum connections to the distributor, changes in timing are ruled out.

It almost sounds like the ECU is trying to change the mixture based on O2 feedback but the O2 sensor is slow to respond causing periodic lean or rich episodes.

Erik Beeman

Faulty O2 sensor?

abecedarian

Possibly. Or faulty heater circuit on the O2 sensor, which may be wiring related or could be the sensor itself.
But I can't say for sure. It just sounds like it.

I had a VW Scirocco with Bosch K-Jetronic injection and it has a 'frequency valve' on the injection body. It responds to the O2 sensor, so if the O2 said rich, it bled off pressure to go lean and held pressure if the O2 said lean in order to enrich the mixture. Basically the frequency valve's operation was measured in "duty cycle" so if the valve was open and closed for the same amount of time, that was a 50% duty cycle. As the O2 sensor would age, you'd find the duty cycle drifting away from 50% towards 60-70% implying the engine needed to run leaner which wasn't at all true. It was just trying to keep the O2 readings "normal".

The EFI on our trucks, though it operates similarly, doesn't have that valve so it has what's called "fuel trim". The fuel trim value is a calculated adjustment / offset to what the ECU thinks it should inject in order to compensate for intake or exhaust leaks, faulty injectors, or just about anything affecting fuel mixture. When you reset the ECU, the fuel trim goes to zero meaning no alteration to the mixture, but as time goes by and the ECU finds the O2 reading a consistantly rich or lean mixture, the ECU will alter the fuel trim in order to get the O2 sensor readings fluctuating equally between rich and lean readings (50% duty cycle). And when the fuel trim amount cannot be adjusted any further to keep the O2 sensor reading 50/50 rich/lean, the O2 related codes get thrown.

There are two levels to fuel trim- one is a long term setting and the other is more closely related to the last time the engine started. The first basically deals with things like engine wear, etc. and the latter deals with things like leaving the Pacific coast and travelling up to Mammoth. The latter influences the former if the ECU finds itself adjusting more away from the basic fuel trim. In essence if you spend most of your time at sea level and take occasional trips to the mountains, the ECU can compensate for it but as you spend more time in the mountains, the ECU will start adapting more for high-elevation operation.

Just realized I got long-winded and probably more 411 than you needed so... hope this helps.

Erik Beeman

Very good info. To me, there is no such thing as too much info. I sit at the computer and read read read all day about everything I can to gain as much knowledge. Just like I always say...this may not be usefull to me now, but somewhere down the line, it will be.


Is the ECU resettable?

abecedarian

Well I do tend to babble a bit if left unchecked.Yeah. Disconnect the battery for a short period of time, but closer to the 15 minute or so mark.

TinMan

Do you have factory service manual? If not there are several links on posts around here that will lead you to one. Once you get one, go to 4crawlers web site (google 4crawler cheap tricks) and read his posts about TPS , and AFM. My 85runner does a lot of what you are talking about. I tested the TPS by the FSM and 4crawlers site, and it is bad. If it tests bad there is nothing you can do about it except replace it. Kind of a pain in the but to test, but once you understand it, it is not to bad.