Oversized injectors with stroker engine and fuel trend

[1515art]

I’m wondering if I’m over looking the obvious here with regard to my fuel trim. Now that I’ve corrected most everything I can by changing sensors, fixing vacuum leaks, connecting grounds and switching computers I’ve been pulling my hair out and on the verge of taking a loss by dumping my Tj still trying to get my fuel trim reading where I think it should read. All,of the things I have changed for the most part needed replacing and the intake manifold being loose was also necessary to correct, I expected after taking care of the intake manifold leak everything was going to fall in place but not yet, or so I have thought. Last night I switched in all 4 of my computers expecting the fuel trim to be where it should checking my 1st wrangler fix PCM live data and the fuel trim looked perfect, the o2s up stream also looked good but the down stream voltage near the high point .7-.8 still in range. The other 3 gave high negative fuel trim data combined short term long term in total -14 to -18 out of normal range, the O2s numbers were better than the first computer I had tuned.

im now unsure if for my stroker with its oversized injectors at idle anyway I actually should expect the fuel trim to be a higher negative number? Everything I’ve done has been trying to duplicate normal fuel trims but my Jeeps not stock.

a couple issues can cause high negative fuel trim bad o2 sensors or bad injectors, a faulty PCM as well but having 4 different computers to try I think I can rule that out. The sensors seem to be operating correctly and this takes me to the injectors. Should they actually be high negative numbers since they are oversized to meet higher demands of the stroker at higher rpm situations but at idle the fuel demand is same as stock 4.0.

and if the computer I had tuned is giving normal fuel trim is that actually leading to the fuel washing bu not dialing back the fuel when not needed by the o2 sensor data?

what do you think, is the higher negative fuel trim using the oversized injector with the stroker actually what it should be?

 

[Chris]

I didn't realize you had a stroker. Have you talked to Golen or any of the other stroker builders about this? I suspect they would know the answer to this question. I've heard some say you don't need bigger injectors with the stroker engines, but I don't see how that can be true.

Clearly it isn't your PCM, I think you can rule that out as you said.

 

[Wildman]

Are you expecting your PCM to just adjust for you or do you have a TUNE from a Tuner like FRP or HemiFever writing a tune for you? A stock PCM can't make adjustments for a modified engine past a very small part.

 

[1515art]

Well, I have been in contact with Chad at Golen from the start and I’m guessing it’s just never been an issue I didn’t get any codes to start with and never would have even known my fuel trims were negative high taking fuel away had I not had so many issues going on at once so I’d guess it’s never been noticed? The injectors and oversized throttle body were a part of the package I bought with the engine.

My oil after the tune on my first wrangler fix PCM was getting fuel washed I think because the PCM was not being allowed to compensate for the increased fuel delivery not needed at idle, the Fuel trims set by the tune below 5, making it run rich, contributing to the oil taking on fuel. The injectors are obviously a mechanical change I guess like a leaky injector would also cause a rich condition and the PCM will compensate showing high negative numbers but in my case I guess that’s the point and I think now that might eventually balance out with the LTFT driving at higher RPM, most everything now has been at idle when the stroker fuel demand is low?

this make sense?

 

[Chris]

Are you expecting your PCM to just adjust for you or do you have a TUNE from a Tuner like FRP or HemiFever writing a tune for you? A stock PCM can't make adjustments for a modified engine past a very small part.

This is a good point.

I've heard some say that the stock PCM can handle a stroker engine without a tune, but that's absolute bullshit. Sure, it might be able to do it, but the bottom line is that you're giving it more air, and so you want to give it more fuel. The compression is raised so it should be expecting this as well.

If it were me I would be sticking this thing on a dyno and having a competent tuner with HPTuner experience tuning it so it's running optimally.

 

[Juggernaut]

Just so I’m following correctly - 3 PCMs give negative trims and the 1 pcm you had tuned gives normal trims but still has fuel washing?

I assume you don’t have a wideband? What are you running for a cam?

 

[1515art]

according to Chad no tune is needed and he supplied the throttle body and injectors.

I will have to look up in my paper work but the cam is standard to his builds.

the tuner I hired said it was running rich meaning high - trim but setting the PCM to 0 or positive would have the opposite effect over riding the data from the o2 sensor stopping the PCM from leaning the engine out? The injectors are only a little larger so as long as it was left alone the PCM can probably handle the difference and why it’s not been an issue In the past builds?

 

[1515art]

I’m going to put the new wrangler fix PCM back in drive it some and carefully see how it goes, I think the negative trim right now between -14 to -18 at idle wil find a place slightly lower as more data is fed to the LTFT. And the negative trim at is actually closer to normal considering the PCM really has know way of knowing the injectors are larger just that when the extra fuel isn’t needed it being told to lean out the fuel ratio.

 

[Juggernaut]

You mentioned vacuum leaks -You sure they are fixed? Any leak, especially after the MAP will only confuse the O2s.

I assume you are operating in closed loop and your Tuner is referring to adjusting the Volumetric Efficiency tables to reflect what your short term and long term fuel trims are indicating. Your tune shouldn't be that far off. A basic rule of thumb is +/-5%. You're well outside that, and assuming everything is mechanically sound ( no vacuum leaks or leaking injectors puddling fuel), you should look to readjust your VE tables based on the cumulative total of the short term + long term fuel trim values or look at adjusting the pulse width.

 

[Wildman]

Do you have a Air/Fuel ratio gauge on your rig? So you can monitor the readings as you drive?

 

[SkylinesSuck]

Do you have a Air/Fuel ratio gauge on your rig? So you can monitor the readings as you drive?

This.

If you are trying to tune via throwing bigger injectors in and looking at your fuel trims, you going about it bass ackwards.

Do you have a wideband? And if Rubicon88 pops in with input, ignore whatever he says

 

[1515art]

You mentioned vacuum leaks -You sure they are fixed? Any leak, especially after the MAP will only confuse the O2s.

I assume you are operating in closed loop and your Tuner is referring to adjusting the Volumetric Efficiency tables to reflect what your short term and long term fuel trims are indicating. Your tune shouldn't be that far off. A basic rule of thumb is +/-5%. You're well outside that, and assuming everything is mechanically sound ( no vacuum leaks or leaking injectors puddling fuel), you should look to readjust your VE tables based on the cumulative total of the short term + long term fuel trim values or look at adjusting the pulse width.

Sorry this took so long been a busy day, I haven’t had a chance since doing the first smoke test it initially showed leaks in 2 places aronud the valve cover and around the throttle body butterfly shaft, the major leak was from the first few intake manifold bolts, that was pretty significant. I paid a shop to swap out the manifold gasket I’m pretty certain they did a good job and I’m planning to smoke test tomorrow. I tightened the valve cover bolts the throttle body butterfly is ahead of the MAP and I believe the 2-06 has a air charge temperature sensor instead of a MAF its new, throttle body sensor new, map is new and the IAC is new as are all 4 o2 sensors.

 

[1515art]

It’s in closed loop and all the other live data l think is good.

I noticed on the wrangler fix website they recommend against tuning at risk of corrupting the programming.

rather than typing in the engine specifications this is a generic build sheet:

Do you have a Air/Fuel ratio gauge on your rig? So you can monitor the readings as you drive?

all I have to monitor driving is my OBD2 reader live data after I get a chance to switch the PCM I’ll get some screen shots.

This.

If you are trying to tune via throwing bigger injectors in and looking at your fuel trims, you going about it bass ackwards.

Do you have a wideband? And if Rubicon88 pops in with input, ignore whatever he says

I do many things ass backwards this one was sent to me this was so I had to do all the other things that way, lol.

The challenge was I had all really old sensors, that should never have been switched onto the new stroker, the radiator used was aftermarket, the engine ground strap was unconnected, the transmission and torque converter were slipping/shuddering, bent rear axels, driveshaft issues and the front and rear pinion angles were way way off.

all this stuff all caused drive ability issues and had to be picked off one at a time and got me to the OBD2 live data, then the tuner, followed by the new (4th) PCM.

im not sure what a wide band is?

 

[Wildman]

It’s in closed loop and all the other live data l think is good.

I noticed on the wrangler fix website they recommend against tuning at risk of corrupting the programming.

rather than typing in the engine specifications this is a generic build sheet:


im not sure what a wide band is?

https://www.summitracing.com/parts/...2077271614146&utm_content=GSAPI+5ba0fb517989d
To get a true reading of your air fuel ratio you need a wide band O2 senor like what is used with this gauge. You'd have to add a second bung to your exhaust so it can read your exhaust. This gives a better reading than the stock O2 sensors. They aren't wide band.

 

[SkylinesSuck]

Narrow band O2 sensors can only say leaner or richer than 14.7 and thus are only useful for closed loop i.e. part throttle. You need a wide band O2 sensor because it will actually tell you what's your a/f ratio is from 10:1 to arrive 20:1. You can't (reasonably) tune without one.

The way people have been getting away without tuning our strokers (with milder cams and stock'ish compression) is that they throw bigger injectors in that are known to get things kinda ballpark right at WOT with the stock fuel mapping because they are bigger. The ecu doesn't know they are bigger so it opens them up the same amount but more fuel goes in than it thinks because bigger. The ecu has no idea more fuel is going in at WOT. Normally that would make things rich across the board but the ecu can look at the factory narrow sensor in closed loop (part throttle) and see too much fuel is going in and pull it back. That is why your fuel trims are off (probably). The ecu only (kinda) sees what's going on at part throttle, not WOT and is trying to adjust within it's factory parameters. That will also affect WOT I think? But not much, hence your engine no go boom.

Bottom line is, get a wide band O2 sensor and see what is in fact going on.

 

[Wildman]

 

[Juggernaut]

Narrow band O2 sensors can only say leaner or richer than 14.7 and thus are only useful for closed loop i.e. part throttle. You need a wide band O2 sensor because it will actually tell you what's your a/f ratio is from 10:1 to arrive 20:1. You can't (reasonably) tune without one.

The way people have been getting away without tuning our strokers (with milder cams and stock'ish compression) is that they throw bigger injectors in that are known to get things kinda ballpark right at WOT with the stock fuel mapping because they are bigger. The ecu doesn't know they are bigger so it opens them up the same amount but more fuel goes in than it thinks because bigger. The ecu has no idea more fuel is going in at WOT. Normally that would make things rich across the board but the ecu can look at the factory narrow sensor in closed loop (part throttle) and see too much fuel is going in and pull it back. That is why your fuel trims are off (probably). The ecu only (kinda) sees what's going on at part throttle, not WOT and is trying to adjust within it's factory parameters. That will also affect WOT I think? But not much, hence your engine no go boom.

Bottom line is, get a wide band O2 sensor and see what is in fact going on.

Skyline you are absolutely correct - the long term fuel trim seen by the O2s in closed loop are carried over into open loop at WOT which only makes your WOT fueling off as well. Tuning closed loop with o2 can be done but it's a lengthy undertaking, not nearly as accurate, and can't help you tune WOT. A wideband really is the way to go to ensure your getting the most out of the money you've spent.

 

[1515art]

is one sensor the way to go and then attach the bung on the #1bank or placing the bung a the junction where the two sides interconnect, or should i go with a dual wide band sensor a have readings for both banks?

looking at the wide band kit if I wanted to do both banks it looks like using two single sensor kits is less $$ if that’s needed.

 

[Wildman]

is one sensor the way to go and then attach the bung on the #1bank or placing the bung a the junction where the two sides interconnect, or should i go with a dual wide band sensor a have readings for both banks?

I'd have to pull out my instructions but I am pretty sure you put it down where the two banks have come together. I think if you wanted to get REALLY accurate tuning you could install 2 sensors with 1 on each bank.


https://www.aemelectronics.com/site...tions/30-4110_Digital_Wideband_UEGO_Gauge.pdf

A weld-in M18 X 1.5 boss is supplied for sensor installation. Mount the O2 sensor in the exhaust system at least 18 inches downstream from the exhaust port. If you anticipate high EGT's (over 800C), run a turbocharger, run at high RPM for extended periods of time or plan on running leaded race fuel then you must mount the sensor at least 36 inches or more downstream of the exhaust port as all of these can cause the sensor to overheat. On turbocharged engines the UEGO sensor must be installed after the turbo charger, if not, the pressure differential will greatly affect the accuracy of the unit. For accurate readings, the sensor must be mounted before catalytic converters and/or auxiliary air pumps. To prevent collection of liquids between the sensor housing and sensor element during the cold start phase, the installation angle should be inclined at least 10° from horizontal with the electrical connection upwards, see below. (Figure 8)

 

[Juggernaut]

Mine is located very close to where the two come into one. While not in the text book ideal position, I have found that it reads accurate and confirmed with a tail pipe O2.