Faulty Fuel Injector causing mis at startup?

[JerrySab]

I'm so sorry. HEGO Heated Exhaust Gas Oxygen Sensor, and in my foggy Sunday brain I truly meant to reference the Air Charge Temp Sensor. which plugs into the side of the intake plenum, and can easily become undone or not reconnected firmly after injector work.

 

[eightynine4x4]

I'm so sorry. HEGO Heated Exhaust Gas Oxygen Sensor, and in my foggy Sunday brain I truly meant to reference the Air Charge Temp Sensor. which plugs into the side of the intake plenum, and can easily become undone or not reconnected firmly after injector work.

Are we sure that the HEGO in my 89 is in fact the ACT? The Air Charge Temp? I did replace the ACT sensor. It’s got two wires too, so I assume it has ground regardless if quality of mounting. But regardless of ground, I’m confused because I thought that the ACT sensor was just temperature reading of air intake.

So, whenever I see HO2S I think in my truck it’s the O2 sensor, since that’s the only sensor that would read a chemical/gas balance or whatever, as opposed to just temperature. When I see these codes saying lean, I associate it with the gas coming out of the exhaust being read by the O2 sensor, not the temp of air in intake.

I’m happy to be wrong though!

 

[rusty ol ranger]

The O2 sensor and intake air sensor are seperate.

Your O2 is a 3 wire setup.

The ACT only reads incoming air temp and i highly doubt thats your issue.

@RonD can explain this better to you then i ever could, but you should check the voltage going to the O2 and the voltage coming out of the O2 and verify that voltage is getting to the ECM.

I believe a O2 drops voltage when lean, so what im getting at is if the ECM is getting a low or zero voltage from the O2 (due to a bad wire) its going to think the engine is lean, so its going to pour fuel to compensate, once its dumping all the fuel it can and the ECM says "what the hell is going on" it threw the adaptive fuel code.

The engine is now taking in enough fuel to compensate for a massive amount of air that isnt there, and its flooding itself.

 

[eightynine4x4]

The O2 sensor and intake air sensor are seperate.

Your O2 is a 3 wire setup.

The ACT only reads incoming air temp and i highly doubt thats your issue.

@RonD can explain this better to you then i ever could, but you should check the voltage going to the O2 and the voltage coming out of the O2 and verify that voltage is getting to the ECM.

I believe a O2 drops voltage when lean, so what im getting at is if the ECM is getting a low or zero voltage from the O2 (due to a bad wire) its going to think the engine is lean, so its going to pour fuel to compensate, once its dumping all the fuel it can and the ECM says "what the hell is going on" it threw the adaptive fuel code.

The engine is now taking in enough fuel to compensate for a massive amount of air that isnt there, and its flooding itself.

Gotcha. Yeah i was just getting confused and trying to definitively associate the HEGO code with either the O2 sensor or the air intake sensor.

I’ve gotta get to the bottom of this. There are two things on my mind about it..

1, I want to make sure things look ok with the throttle position sensor voltages and with the idle set screw. I may have contaminated my TPS when I took it all off the plenum and cleaned it. I realized later that I used a penetrant-lubricant on its little rotating mechanism, not even thinking about the fact that it may not be perfectly sealed and that the potentiometer inside may now be contaminated. I think that if the balance of fuel and air is way off due to bad throttle setup, maybe that’s making me run weird and also unsteady during idle due to jumpy potentiometer in there. As for the idle screw, after the TPS testing i may give this a shot. One of my codes is low idle, so maybe my screw has been off this whole time ..https://www.therangerstation.com/forums/index.php?threads/how-to-2-9-idle-adjustment.196011/

2, I want to do a thorough test at my O2 sensor and wires. But I also have a related concern which is that my gasket (edit: connection point) from Y pipe to cats is leaky and the O2 sensor is quite close to that. I know that the exhaust is constantly pushing air/gasses passed the sensor and away but I’m wondering if somehow the exterior atmosphere is still bringing enough oxygen upstream to sensor to make the sensor read LEAN (which I believe is indicated by high oxygen not low oxygen)

 

[rusty ol ranger]

Gotcha. Yeah i was just getting confused and trying to definitively associate the HEGO code with either the O2 sensor or the air intake sensor.

I’ve gotta get to the bottom of this. There are two things on my mind about it..

1, I want to make sure things look ok with the throttle position sensor voltages and with the idle set screw. I may have contaminated my TPS when I took it all off the plenum and cleaned it. I realized later that I used a penetrant-lubricant on its little rotating mechanism, not even thinking about the fact that it may not be perfectly sealed and that the potentiometer inside may now be contaminated. I think that if the balance of fuel and air is way off due to bad throttle setup, maybe that’s making me run weird and also unsteady during idle due to jumpy potentiometer in there. As for the idle screw, after the TPS testing i may give this a shot. One of my codes is low idle, so maybe my screw has been off this whole time ..https://www.therangerstation.com/forums/index.php?threads/how-to-2-9-idle-adjustment.196011/

2, I want to do a thorough test at my O2 sensor and wires. But I also have a related concern which is that my gasket (edit: connection point) from Y pipe to cats is leaky and the O2 sensor is quite close to that. I know that the exhaust is constantly pushing air/gasses passed the sensor and away but I’m wondering if somehow the exterior atmosphere is still bringing enough oxygen upstream to sensor to make the sensor read LEAN (which I believe is indicated by high oxygen not low oxygen)

The TPS thing is a good idea. But i would only try to set idle with that screw as an absolute last resort. You have verified proper IAC function right?

The Y pipe to gasket leak maybe some of the issue causing the lean code, because yes lean means high oxygen content, due to not enough fuel. If some of the fumes/gases are escaping before the O2 then this could happen, personally though my truck sets a lean code i blame on the junk exhaust and it runs fine.

That being said though, you have mutiple codes relating to a O2 sensor that you replaced. The fact that it throws the switching code, as well as the HEGO code, in addition to the lean code really leads me to believe its a wireing issue.

The bad exhaust gasket might throw a lean code, but its not going to set off the HEGO or switching code.

 

[eightynine4x4]

The TPS thing is a good idea. But i would only try to set idle with that screw as an absolute last resort. You have verified proper IAC function right?

The Y pipe to gasket leak maybe some of the issue causing the lean code, because yes lean means high oxygen content, due to not enough fuel. If some of the fumes/gases are escaping before the O2 then this could happen, personally though my truck sets a lean code i blame on the junk exhaust and it runs fine.

That being said though, you have mutiple codes relating to a O2 sensor that you replaced. The fact that it throws the switching code, as well as the HEGO code, in addition to the lean code really leads me to believe its a wireing issue.

The bad exhaust gasket might throw a lean code, but its not going to set off the HEGO or switching code.

Great info and great point, thank you!

I guess I’m also trying to figure out if I now have two distinct issues or if it’s rolled into one. The lean situation make sense, could be wiring or even bad luck with new sensor. But the wavering idle, even after warmup, seeming indecisive what RPM to stay at, changing its mind every few seconds…. Could/would the computer really do that based on lean O2 readings? Like I get that the injectors would send too much fuel per send, but would it also choose to adjust the RPM wildly? If not, then I think I’ve got two situations. The low idle code thrown is significant.
And yes I just put on a new IAC this week. Didn’t test it manually but I do vaguely recall there’s a way to do that. But assuming it works, the IAC isn’t the cause.
I do wonder about previous owners messing with the set screw though. There’s nothing marking a factory setting so I have no way of knowing if someone hastily cranked it up or down to solve a problem out on a trail or something. I won’t touch it for now but at some point will probably end up marking its current setting and doing the above mentioned shop notes adjustment just to see where things end up and maybe resort to where it currently is.
But first I’m gonna focus on O2 wiring /circuit testing and TPS wiring / circuit testing.

 

[rusty ol ranger]

Great info and great point, thank you!

I guess I’m also trying to figure out if I now have two distinct issues or if it’s rolled into one. The lean situation make sense, could be wiring or even bad luck with new sensor. But the wavering idle, even after warmup, seeming indecisive what RPM to stay at, changing its mind every few seconds…. Could/would the computer really do that based on lean O2 readings? Like I get that the injectors would send too much fuel per send, but would it also choose to adjust the RPM wildly? If not, then I think I’ve got two situations. The low idle code thrown is significant.
And yes I just put on a new IAC this week. Didn’t test it manually but I do vaguely recall there’s a way to do that. But assuming it works, the IAC isn’t the cause.
I do wonder about previous owners messing with the set screw though. There’s nothing marking a factory setting so I have no way of knowing if someone hastily cranked it up or down to solve a problem out on a trail or something. I won’t touch it for now but at some point will probably end up marking its current setting and doing the above mentioned shop notes adjustment just to see where things end up and maybe resort to where it currently is.
But first I’m gonna focus on O2 wiring /circuit testing and TPS wiring / circuit testing.

Absolutly. Id get it running good first then worry about the idle.

The O2 shouldnt play into it when cold. The ECM ignores the O2 till engine hits a certain temp (150 IIRC).

If its not getting ANY o2 reading though...im not sure what it would do.

I did the screw adjustment on mine because i had issues before that i tried to cover up the best i could by bumping the idle up. Once i got those issue squared away i readjusted it according to the proper procedure and it idles pretty damn good now.

Im sorry if you mentioned it but you have replaced the MAP sensor correct?

 

[eightynine4x4]

Absolutly. Id get it running good first then worry about the idle.

The O2 shouldnt play into it when cold. The ECM ignores the O2 till engine hits a certain temp (150 IIRC).

If its not getting ANY o2 reading though...im not sure what it would do.

I did the screw adjustment on mine because i had issues before that i tried to cover up the best i could by bumping the idle up. Once i got those issue squared away i readjusted it according to the proper procedure and it idles pretty damn good now.

Im sorry if you mentioned it but you have replaced the MAP sensor correct?

Proper procedure meaning the same set of instructions I linked to a few posts ago? If not, would be great to see the procedure you’re referring to.

Yes I replaced the MAP right away when i got the truck a couple years ago.

I just went and took readings of the TPS output signal and it seems to move fine. The starting point seems a bit high, at 0.955 VDC. But pushing the slowly, it travels smoothly all the way up to exactly 4.5 VDC at WOT. I know that the computer gradually re-learns the bottom of the voltage and adjusts this accordingly. And I wonder if every time I unplug the battery I am resetting this “bottom idle voltage” to the computer’s default of say 0.5 and thus throwing off the idle until the computer has had enough driving action to relearn 0.955 instead of something 0.5. I suppose if this is the case, every single time you work on your truck you have to accept that idle may be wonky for a while after. But if this high start voltage is above what the computer is expecting for idle, I think it would idling fast not slow. So I don’t get it. Or, maybe 0.955 is in fact too high and I need to address this?
But if it’s not the TPS, MAP, ACT, IAC or O2 (since during warmup it’s cold and ignored), I’m not really sure what else to attribute wild or low idle to other than the computer is trying to sort something out and needs more repetition to do so, without disconnecting the battery for a number of drives.

 

[rusty ol ranger]

It depends how long you unhook the battery. I think it takes like 30 minutes for the ECM to reset.

I used the procedure you linked to...i actually posted that post lol.

As far as TPS voltage anything under 1v i believe is fine. So you should be good there. IIRC thats what mine rides at.

If none of the sensors fixed it...its either wireing or possibly the ECM itself.

 

[rubydist]

Immediately getting a lean code after doing the various things you have done suggests that you still have a vacuum leak somewhere.

If you don't have a vacuum leak, then replacing the oxy sensor would be the next step in my diagnosis.

fyi, it will take a while for the engine to "learn" the correct idle setting for the new iac, so the low idle speed and lumpy idle are to be expected for a while. I have had it take as long as a week of driving for that part of things to get sorted out, so be patient with that.

 

[eightynine4x4]

It depends how long you unhook the battery. I think it takes like 30 minutes for the ECM to reset.

I used the procedure you linked to...i actually posted that post lol.

As far as TPS voltage anything under 1v i believe is fine. So you should be good there. IIRC thats what mine rides at.

If none of the sensors fixed it...its either wireing or possibly the ECM itself.

Ha! It WAS you!
Yes I am still curious about the ECM itself. I posted a pic of my ECM on this forum last year concerned that I had the wrong model since it says the wrong truck specs on it, but folks here said it would work fine and/or function the same. That doesn’t mean it’s not faulty though. Clearly it was a replacement itself. Maybe I should just replace that too. At that point all of my digital system and sensors will be new, ha!
Anyways, my truck is 1989 4WD automatic. The ECM pictured below has 2WD hand written on it. Likely this handwriting means it was pulled from a parts truck.

Immediately getting a lean code after doing the various things you have done suggests that you still have a vacuum leak somewhere.

If you don't have a vacuum leak, then replacing the oxy sensor would be the next step in my diagnosis.

fyi, it will take a while for the engine to "learn" the correct idle setting for the new iac, so the low idle speed and lumpy idle are to be expected for a while. I have had it take as long as a week of driving for that part of things to get sorted out, so be patient with that.

I replaced the O2 sensor a year or so ago. I have a vacuum gauge in the cabin permanently hooked up to plenum that reads 18-21 during idle and also indicates healthy activity during throttle operation, so I can only assume it’s not a major vacuum leak or id see it there in the gauge right?

Id be ok with ignoring the idle issues and just driving the truck for a while but I’m getting a check engine light now after this work where as that light hadn’t turned on for like almost two years now. I’m not super enthused about driving the truck lean if it is in fact lean.

If I were going to keep throwing parts at it, next up would be spark plugs and ECM.

 

[rusty ol ranger]

4wd to 2wd shouldnt matter.

You bought a junkyard ECM?

If it was a vacuum leak big enough to hit the adaptive fuel limit you would hear it.

Just for shits though...try unplugging your brake booster line at the engine side and plug the port. Long shot from hell,..but you might get lucky.

 

[eightynine4x4]

4wd to 2wd shouldnt matter.

You bought a junkyard ECM?

No this is what was in my truck when I got it a couple years ago. Who knows where they got it.

 

[rusty ol ranger]

No this is what was in my truck when I got it a couple years ago. Who knows where they got it.

Crack the case on the ECM and see if you see any obvious damage.

 

[eightynine4x4]

Crack the case on the ECM and see if you see any obvious damage.

I took it out to lay in the sound absorption material you see there in pic. It’s annoying enough of a project that I’m tempted to just replace it if I’m already opening it up haha. Oh the fun world this is.