That i have not checked. Nor have the equiptment to check it . I was thinking it might be the fuel pump, but if it was it wouldnt run at all. Fuel pumps just dont partially run, they run or they dont.

I guess i could buy another fuel filter. Not too costly but i changed that less that 10k ago. sooner than that even. I need to start writing these things down lol

 

Only reason i say that is becuase a guy with a dodge just called me saying that the smt6 is causing problems...i asked what was going on and he says that the fuel pressure drops to 5psi when under load and the afrs go whack....i dunno how the smt6 could cause this but ill send him a new one anyway to ease his mind....
Thats the reason that thought came to mind...if all the electronics have been tested and you loose afrs badly then fuel pressure is one thing that can cause it.
Fuel pumps do output less in some cases and if you are supercharged using the stock fuel pump you will loose fuel flow if the pump is old... of course MOST just die...but hey i like to think outside the book sometimes!
Now its a matter of figuring out a way to test FP without hacking the fuel system to ▓▓▓▓...

rdharper,
The ecu will pull lots of timing when under sever load...the fact that his timing is going WAY back is kinda odd...i still think ecu...

 

i have the walbro 190 fuel pump

 

Ah then thats no problem...gay....you got an odd problem

 

"New" I gotta figure is around $500 - if the donor fixes my issue, I'll be aiming at a junkyard, probably $150ish.

Oh, well then... My 3rd is leaking too; all four boots are torn on the CVs; one of them is pretty dry; my methanol injector system is leaking; my steering rack's been in need of a good swapping for well over a year; the front sway bar is off 'cause the bushing are so worn it's safer with it off.

I miss driving my deathtrap...



Yeup it does, but given that the timing is dead-on at idle (as checked with a light), and you see things like the reported MAF airflow jumping by a factor of 8 with just the SLIGHTEST of additional pressure on the throttle (we're talking curling my toes). There's no way that the engine is suddenly sucking that much more air.

Point being from Johnny, is that the ECU is possibly reacting to what it believes is a sudden in-rush of air. Thus, it's retarding the timing and throwing fuel, which (since there really isn't that much more air coming in) bogs the engine down to sputtering.

Now, if the in-rush isn't really there, then the MAF is lying, the wiring is shorting out, or the ECU is freaking out. Having the same symptoms with three different MAFs, and each of those MAFs works fine in another truck, we can kinda' eliminate the MAF itself.

Wiring wise... It seems weird that a wiring problem would only show itself at this tight of a threshold. This is repeatable within 100rpm no matter if I'm driving on a flat/level road or going up/down hill. It really seems RPM related or possibly TPS. But, the TPS checks out via OBD and DMM, and I have the same symptom with another TPS.

But then... this doesn't happen with the truck in neutral in the driveway, so it's probably not strictly RPM related. sigh.


You mean, I shouldn't have practiced my backswing with that 10lb sledge? Crap, now ya' tell me!


Oh, I KNOW... In all, I've had 4 problems that I've found and fixed (so far) while looking for "the big one". Ignition controller; cat; exhaust leak; coil pack. All guaranteed shot, replacement of each made things "better" but not fixed.

 

Update..

Well, the donor ECU I got was out of a 97 and my truck didn't even start with it. D was hoping it might, but no good. I'll have to go fishing. fwiw 89661-3D150/175000-8391 is what I'm looking for.

Dropping the SMT back in the line shows that the MAF voltage is _normal_ at the point that "it" happens. I'm running along showing 3.17v, curl my toes, engine spits, OBD freaks (i.e., fuel trims up, load skyrockets, etc), MAF voltage drops to 2.89, 2.74, 2.19 etc as the engine sputters. I think this proves that it's not the MAF itself nor the wiring from there to the ECU. Moreso, given that OBD is reporting that the ECU thinks a TON of air is coming in, and a voltage shows that info ain't coming from the MAF, then yeah, i gotta find an ECU.

Good suggestion Johnny - thanks!


I have the wiring harnesses to check, and even though the TPS shows good through OBD, I have one here, so I might as well swap it, right?

This on-the-edge threshold thing is SOOOOOOOOO weird. It's 100% repeatable, RIGHT at the same point. I really harp on that, but I have to believe that it means SOMETHING.

 

To clarify:
P0300 -multiple misfire
P0301 -cyl #1 misfire
P0302 -cyl #2 misfire
P0303 -cyl #3 misfire
and so on...

 

Right... those are (unfortunately) well known P codes to me. I'm not sure what you're saying?

I'm pretty convinced that the misfires (and the stumbling, etc) are a result of the fuel dump.. just gotta narrow down what's triggering the fuel dump.

 

Mark;

I'm still missing something...

Cruising around 2600-2800 RPM:
Load: 16%
Timing: +15*
Short Term Fuel: -3.9%
MAF: 1.29 lb/min

Feather the throttle to make "it" happen:
Load: 97%
Timing: -2.9*
Short Term Fuel: +10.7%
MAF: 10.37 lb/min

The ecu seems to decide to do the equivelant of opening another intake on my truck at around 3k (however thats done on a FI ecu controlled system). So that feather edge would be, I suspect, that event happening. But its the response of your current system I don't get.

Your numbers implie to me that the load (how is load measured?) its trying to handle increases big-time, normally a major acceleration event. I'd expect air intake to increase to handle the extra fuel that implies. But the retarded timing under those conditions doesn't make sense. I'd expect timing to advance. And I'd expect the system to bog if more fuel, more air come in, with retarded timing.

What am I missing?

 

Hey Richard...

Yeup, I agree with you about the numbers moving wrong, but I think that in itself is a hint as to what's up. I dunno that I/we can trust the numbers that OBD is showing. Based on my tests yesterday, we now know for sure that the MAF itself is NOT reporting a mass amount of air coming in, but yet OBD says it is. I think that supports Johnny's theory that the ECU is hosed.

Now, if that much air WAS suddenly coming in, then I would expect the ECU to go "OMG! ADD FUEL!" and the load numbers would peg, and yes, I think the timing would normally advance (though Johnny had a theory as to why it wouldn't). No matter, we know that the air isn't really coming in and that the OBD numbers are fake.


Earlier others had thought that I jumped a tooth on the timing belt, is that what you're thinking? I'm kinda' shaking my head and saying "I dun't tink so" 'cause I know the timing is spot on at idle when checked with a light. If the tensioner was hosed and thus letting the belt slack at speed and then skip, it wouldn't "come back", and my timing would be off at idle.

None-the-less, that mechanical skip wouldn't show up via OBD


Load wise, Johnny says that's a function of the MAF airflow and the TPS position.

 

Mark;

Yeup, I agree with you about the numbers moving wrong, but I think that in itself is a hint as to what's up. I dunno that I/we can trust the numbers that OBD is showing. Based on my tests yesterday, we now know for sure that the MAF itself is NOT reporting a mass amount of air coming in, but yet OBD says it is. I think that supports Johnny's theory that the ECU is hosed.

If the ECU thinks the MAF value is high, rpm's above 2800 (TPS is clearly working, cause it gets that from one of its two sensors), and it dumps in fuel to handle the situation, the ECU would also advance the timing at the same time. (assuming I have the slightest idea of how the ECU is programmed). Therefore I'm still puzzled about the timing.


Now, if that much air WAS suddenly coming in, then I would expect the ECU to go "OMG! ADD FUEL!" and the load numbers would peg, and yes, I think the timing would normally advance (though Johnny had a theory as to why it wouldn't). No matter, we know that the air isn't really coming in and that the OBD numbers are fake.

Ok... I'll go back and see if I can understand Johnnies argument as to how that could be. Do we know if the ECU gets a sensor report on what the actual timing is, or is it open-loop, just telling us what it is setting.

Earlier others had thought that I jumped a tooth on the timing belt, is that what you're thinking? I'm kinda' shaking my head and saying "I dun't tink so" 'cause I know the timing is spot on at idle when checked with a light. If the tensioner was hosed and thus letting the belt slack at speed and then skip, it wouldn't "come back", and my timing would be off at idle.

How about vacuum not working correctly? (I'm over my head here, information-wise) Could it be the default non-load is set correctly, but the timing can't advance properly? This goes back to... where does the OBD get the timing value? Is it what the ECU is seeing, or what the ECU is setting. You may have shown this earlier, but does the timing advance properly under no-load?

 

Mark has me going back reading your posts.... I missed this. Sure would be helpful if we-all knew more about where the OBD gets its info. I expect it is reporting what the ECU sees.

A corollary to that is, is the timing acutally "measured" and fed back to the ECU, or is that number what the ECU is actually trying to set.

 

If the ECU thinks the MAF value is high, rpm's above 2800 (TPS is clearly working, cause it gets that from one of its two sensors), and it dumps in fuel to handle the situation, the ECU would also advance the timing at the same time. (assuming I have the slightest idea of how the ECU is programmed). Therefore I'm still puzzled about the timing.

Agreed (outside of Johnny's theory)... the way the numbers are moving, and the fact that OBD is reporting something that CLEARLY isn't happening (air flow) is pointing to the ECU being hosed in some way/shape/form.



Ok... I'll go back and see if I can understand Johnnies argument as to how that could be. Do we know if the ECU gets a sensor report on what the actual timing is, or is it open-loop, just telling us what it is setting.

Johnny will know for sure, but there's a crank and a cam sensor so (I think) it should be able to figure it out.



How about vacuum not working correctly? (I'm over my head here, information-wise) Could it be the default non-load is set correctly, but the timing can't advance properly?

Are you thinking like "vacuum advance"? Timing advance on these engines is electronic, it's the ECU controlling when the spark coils are firing, so there's no vacuum based mechanical stuff going on. The ability to electronically set the timing is behind the principle of how the piggy-back's (SMT, FTC1) work. They delay the cam or crank signal to fake the ECU into advancing/retarding the spark.



This goes back to... where does the OBD get the timing value? Is it what the ECU is seeing, or what the ECU is setting. You may have shown this earlier, but does the timing advance properly under no-load?

I believe it does... but I'm not 100% sure. Of course, that also doesn't make sense.

So if it's a load based issue, (physical load on the engine versus a reference to the computed load that OBD shows) then is this all actually a tranny issue? I don't "think" there's any feedback from tranny sensors to the ECU in order to gauge physical load. But, I know that this RPM threshold "switch" and all the symptoms will occur at any physical engine load. I can be in a flat-terrain cruise and it'll act the same way as that 11% grade.

 

Ok i wont be able to answer everything but ill see what i can do:

The ecu uses only the crank trigger to see where the crank is as far as timing goes. It will adjust the timing according to LOAD....
LOAD is figured using all the sensors but it all starts with the MAF/IAT in our trucks, if we had a MAP sensor then it would be MAP/TPS/IAT. Of course RPM is the other "Axis" as far as load goes as well

Now it is pretty much a rule of thumb that timing itself will change depending on the load...timing will go up up up as rpm/load goes up but depending on th ecu timing will be pulled of some other conditions are met....IE for boost timing retard kicks in as boost increases....Air Temp...timing will be pulled due to the higher risk of knocking...
I have noticed that in our ecu's if you apply a 90-100% load the timing does not go as high as a lower 70-80% this is probably because toyota wanted the engine to last and would rather sacrifice power for reliability (this is why standalone swaps can yield 10+whp with no other changes).

What makes me KNOW its the ecu is that the timing of marks engine is going into NEGATIVE territory...now that NEVER should happen on a normal running engine...especially na....negative timing is used for crazy turbo kids who like to prespool thier turbo before launch (anti-lag or 2 stepping). This explains the misfires and poor engine performance....

As for what you are seeing in the OBD scanner...that is what the timing is currently at...the ecu sets it and it is what its set at....there is no other module that controls timing like in many other vehicles (older mostly) and the ecu is just reading it...

Hrmm let me know if there are any other questions!

 

Weasy2k, whats the deal with mine?? I think youll have a tough time with this one.

 

Johnny;

The ecu uses only the crank trigger to see where the crank is as far as timing goes. It will adjust the timing according to LOAD....
LOAD is figured using all the sensors but it all starts with the MAF/IAT in our trucks, if we had a MAP sensor then it would be MAP/TPS/IAT. Of course RPM is the other "Axis" as far as load goes as well

MAP?

Now it is pretty much a rule of thumb that timing itself will change depending on the load...timing will go up up up as rpm/load goes up but depending on the ecu timing will be pulled of some other conditions are met....IE for boost timing retard kicks in as boost increases....Air Temp...timing will be pulled due to the higher risk of knocking...
I have noticed that in our ecu's if you apply a 90-100% load the timing does not go as high as a lower 70-80% this is probably because Toyota wanted the engine to last and would rather sacrifice power for reliability (this is why standalone swaps can yield 10+whp with no other changes).

Cool... makes sense, and might even be totally right!

What makes me KNOW its the ecu is that the timing of marks engine is going into NEGATIVE territory...now that NEVER should happen on a normal running engine...especially na....negative timing is used for crazy turbo kids who like to prespool their turbo before launch (anti-lag or 2 stepping). This explains the misfires and poor engine performance....

Of course the negative timing is what I was keying off... nice added info here... I'm in danger of learning something here... thanks!

As for what you are seeing in the OBD scanner...that is what the timing is currently at...the ecu sets it and it is what its set at....there is no other module that controls timing like in many other vehicles (older mostly) and the ecu is just reading it...

Very good. So based on that, you think the ECU is setting the reported timing... since it both controls the timing directly, and can read the set result. Am I getting this right?

Hrmm let me know if there are any other questions!

Thanks for the explanation Johnny and Mark. Really interesting problem... if not fun for Mark (to say the least).

 

MAP = Manifold Air Pressure, versus MAF = Manifold Air Flow. It's a different way of figuring out how much air is really coming into the engine.

The upside of a MAP is that it will adjust automagically to things like humidity, elevation and driving in the midst of a tornado - all events where the air pressure changes on its own and it'd be nice for the engine to know about it.

 

^ However MAF beats MAP when it comes to ANY changes...IE cam begins to wear down and the VE of the engine drops the maf will see this as it will notice less AIRFLOW across the sensor and change fuel accordingly...maf is really good..sucks that is restrictive in most cases

 

Thanks guys...should have figured out what MAP was.

If I remember correctly, all the old hotrodders had MAP gauges as a regular gauge. And maybe lots of trucks too.

 

yea speed density (map based) setups are commen in most aftermarket stuff now...just because there is no real restriction in the system vs maf.

Ohh and to add to this threads "woes"
Just did compression test on my engine...200 200 200 200 200 140 ....sucky! it lived a good life tho! 170,000 mi

I am going to decide on what to do with this engine...would be cheaper for me to use all the after market parts vs OEM stuff Can you say forged