Is my engine choking for air? LQ4, SS2, M6

[Frank_Castle]

In the last month or so I've made some big changes to my car. Swapped 4l60 for t56, changed the rear diff and ratio, and did a cam swap with springs. Ive also had a heck of a time with my tuning equipment. My laptop's HD died and I lost most of my tune files and logs (should have backed them up), and my WB sensor crapped out. Now I have everything back in working order and Im having problems figuring out what is going on with my car. It a stock LQ4 with sloppy stage 2 cam, pac1218 springs, ls1 intake, ls1 rails, ls1 28lb injectors, walbro 450, 3/8 gas line, DIY 4 inch CAI with new filter. Before making the cam and trans changes I dailied the car and put almost 18k miles on it but always thought it kinda run like a turd for what it was. Now it still doesn't run how I expected it would. Ive been VE tuning with the wide band and noticed that the WOT areas of the graph haven't really changed since the cam swap, which I thought was strange because it should be pulling a lot more air into the cylinders. Ive also noticed that those areas of the table have always had a drop/leveling off what seemed out of place. injector duty cycle is only at 80% at WOT in 4th and my arfs are still a little rich at less than 12.5. The VCM scanner HP and torque numbers seem pretty low to me as well. What is going on here? The car idles and cruises fairly decent. I still have some occasional stalling on deceleration issues and a strange hesitation when fist taking off but overall it seems pretty drivable. Is there something that Im missing or any suggestions? Should I continue VE tuning, then MAF, timing, etc... or figure this out first.

Wideband: AEM series x logged through AC port
240sx ve tune 4-30-21.hpt
channels 4-17-21.Channels.xml
240sx drive log 4-30-21.hpl

[blindsquirrel]

Is the MAF removed or just failed for VE tuning? Either way, don't log the Mass Airflow channel when the MAF isn't active.

You are right, it should make more than that and there isn't anything obvious like MAP falling off as RPM rises (at the end the MAP is reading ~99kpa baro, WOT MAP is ~95, this is OK). Spark could be a 5-6 degrees higher but that isn't going to find the missing 100lb-ft. The numbers would look fairly decent if it were a 6.0 with only 7 cylinders. I'd be looking for a misfire/dead hole.

I would like to see a logfile of steady acceleration only, say 3rd gear from as low as you can to 5,500 or so. That's something you can easily repeat as you make changes hunting this down. (but don't get arrested just because somebody on the internets told you to do it)

[kingtal0n]

As with previously suggestion above,
1. compression test, write the numbers down to a decimal, 173.5psi, 171.8psi, 168.8psi, etc...
2. inspect spark plugs to make sure they all look identical (as you do compression test take pictures)
3. Dyno tune the vehicle to make sure the displacement and engine config including mileage matches torque

[Frank_Castle]

Thanks for the quick responses. I logged a couple 3rd gear pulls this morning, removing the MAF channel as suggested as I have it failed for VE tuning. I also added a current and history misfire counter to see if that showed anything. I did a better job on the second log file but posted both anyway. I noticed my IAT sensor was reading strange, jumping form 61deg to -36 deg during the pulls. Im not sure if this could be causing any problems but an interesting find. Im letting it cool now and will try to do compression testing in a bit.

240sx drive log 5-1-21 3rd gear pull 1.hpl
240sx drive log 5-1-21 3rd gear pull 2.hpl
channels AFR and cylinder misfire.Channels.xml

[blindsquirrel]

Did you notice the torque takes off like a rocket right as soon as the IAT drops to -36? Weird.

Attach a temporary ground wire between the PCM case and battery negative.

[kingtal0n]

You need to fix that IAT reading. Its probably a bad sensor or bad wiring or poorly plugged in. The OEM ECU makes HEAVY use of the IAT sensor so Absolutely it will WRECK your day if it fails to read properly.

You can't depend on the predicted torque when that happens to the IAT reading. The IAT sensor tells the ECU how dense the air is, so when the air hits -32*F or whatever the computer suddenly thinks the engine is being 'supercharged' by super dense air so the predicted airflow shoots through the roof in terms of mass.

[Frank_Castle]

I didn't notice that actually, I will give that a try.

I just finished doing a compression test. My gauge does not have the sensitivity to report decimals, actually its not very sensitive at all, a lot of guess work.
Cylinder #1
IMG_4453.jpg
IMG_4464.jpg

Cylinder #2
IMG_4467.jpg
IMG_4468.jpg

Cylinder #3
IMG_4458.jpg
IMG_4463.jpg

Cylinder #4
IMG_4469.jpg
IMG_4470.jpg

Cylinder #5
IMG_4460.jpg
IMG_4461.jpg

[Frank_Castle]

Cylinder #6
IMG_4471.jpg
IMG_4472.jpg

Cylinder #7
IMG_4465.jpg
IMG_4466.jpg

Cylinder #8
IMG_4473.jpg
IMG_4474.jpg

[kingtal0n]

1 looks decent. A little too brown for my taste but you must be using narrowbands.
The black ring looks good. The dark spot is typical. I can't see the side but overall it doesn't look like any problems.

1 has 190PSI compression, but you need to know how many compression stroke and what RPM and was the intake open for air to flow easily?
I recommend performing multiple compression tests and making sure each one hits the same number fo times. Count 1... 2.... 3... 4 compression strokes while cranking with all plugs out for example. Do each cyl multiple times and the same number of revolutions.


There is alot of variability between your cyls so either there is some major issue or you simply did not perform the test evenly across all cylinders. This is where experience is crucial. Is there really a 30-40psi difference Or was that just because the test was performed poorly? We don't know, you must provide this data.

Moving on

2. I sense there is something going on, minor perhaps. The white color is a bit broken "chalky" almost, just a hint of whitening around the black ring, seems unnatural but its only 1pic so hard to say. I would say look closer at #2.
Compression is BARELY within spec of #1 , a bit too low. But was that because the engine went around 1 less time? Or what. IDK only you know. You should keep track how many compression stroke as I said above. Right now your commpression data is almost useless. Almost.

#3
A little TOO brown. Looks like a leaking injector is possible. Or a injector flowing too much fuel. The black ring is nice and unbroken. No flakes of piston evident or other issues. Just too rich, more than other cylinders.
Compression is roughly 200 and change on #3. Again, too high? More revolutions? More RPM? The RPM and # of hits are factors here. So you must crank with same battery voltage, same all plugs out, same number of hits.

moving on
#4 Less brown, a bit too chalky for my taste. Too lean? Poor air distribution? Manifold leaking? You need to pressure test the engine, fill the intake manifold with 10PSI of "boost" pressure using and air compressor and find all leaks. I bet #4 is leaking air and others as well to look leaner. Becuase its either leaner from air leaking in or leaner from fuel injector issues. Black ring is broken for some reason, hard to see but that is another issue. Did you touch the black ring with dirty hands? You should be wearing gloves and keeping the plugs VERY clean for these examinations.

#4 showing strong 205psi compression, way higher than 172psi from #2. Again we don't know if that was less hits, less rpm, or what. If #4 is really 205psi and #2 is really 172psi that is NOT within spec, you have an issue with the compression and bottom end possibly. But more likely you just got 1 or 2 extra hits on #4? Repeat test, keep track. IMO


#5 Too Browned up AND chalky appearance is not ideal. Brown from being too rich. Another broken black ring- touched by dirty hands or?
207.5psi compression very strong. Good compresion but how many hits? See you can estimate the decimal you dont need to know actual decimal. WHen you look back at the results you just round up or down and eliminate the decimal anyways, its just for rounding later and the resulting number is VERY close. 208psi is much better than 210 or 200 written down.

#6 Another strange chalky result. Plugs look like they've been through hell, maybe you tuned on these before using them for a long time? Tuning often causes crazy plug wear and tear. You cant go by plug condition after tuning the engine. You are supposed to TUNE the engine and THEN install new plugs, and Finally check those plugs after using them on the tuned engine. If you tune the engine, then drive the engine, THEn check the plugs you tuned on... they will look like this, all messed up.

190PSI is close enough to 200 and 205PSI that it is within spec for those.

#7 is like #6, too chalky too browned, broken black ring. Not a coincidence. If you tuned the engine on these plugs it would explain this coloration. Otherwise there is some other issue.

172PSI is troubling. Too low to be compared with 205psi from other cylinders. YOU need to sort this out, is it really that low? Or was the test just done poorly. Try again IMO This is how we learn right?


#8 is the worst plug. It looks terrible. I dont know what caused that look. It almost looks DIRTY Like you rubbed it in some kind of dirt. There may be some oil leak or something there. 180PSI compression though, troubling because if there was an oil leak you would expect a high compression reading and a wet plug wet with oil.


180PSI is also very far from 205psi. Too far.

I recommend:
1. repeat the test follow my direction from above, Keep track of # of compression hits and repeat the test for each cylinder to make SURE Your reading is correct. I also recommend using a different compression tester and compare them to make sure yours is correct.

2. Install new plugs, put some miles on them without changing the tune around, and then check them. Use CHEAP COPPER NGK plugs like $2/ plug get some TR6 or similar. Those plugs look like they have been through hell and don't really tell much other than there seem to be some vacuum leaks or injector issues possibly POSSIBLE.

3. Pressure test your intake
https://www.youtube.com/watch?v=rYZmZqn3-x0&t=1s


Confirm the leaks on those cylinders where the plugs are whiter than others. If you don't find leaks you are looking at cleaning the injectors asap.

[kingtal0n]

So here is possible outcomes, so you dont need to wait for a response you can just refer back to this once you've done as outlined.

Two possibilities from compression outcome:
1. When re-doing the test you find all cylinders are not within say 5 to 7% of each other. For example 208 vs 175psi is over 15% different. If you get 208 from one cyl the minimum number from any other cyl is around 208*.07 = ~15psi off, so 208 - 15 = 193psi minimum expectation.


If you don't get at least 190 from every cyl then there is likely some issue with the cylinder. For example some seafoam could bring numbers back if the valves are just gummed up with sticky tar-like substances. If there is some issue with a ring or cyl wall It will require some new rings/hone obviously. A valve job or valve cleaning could bring the compression back so def try seafoams and alternative medicines before rebuilding rofl. If the engine runs and sounds good, its fine no matter what the compression says usually. Also, Some 100% distilled water injection (with maybe 10-15% methanol is okay) would help keep them cleaner so you never have to resort to seafoam like stuff. Also running the engine more carefully at 15:1 and 15.2:1 air fuel ratios will help keep the carbon deposits down for IDLE and CRUISE which is where most of that happens. The narrowbands correct but it takes some time for them to correct, and when they DO finally learn the correct fuel trim value it is a number that can easily reach 14.3 and 14.5 on occasions which is helping deposit carbon to all surfaces.

Why is having different compressions bad for an engine? It upsets the natural rhythm of rotational forces within the atomic crystalline lattices that compose materials of the bottom end. In other words the uneven force transfer will induce vibration at some frequencies not measured by the OEM engineers which means they will go largely undampenedded, that word which means we have absorbed and cancelled that wave wherever it was. Those vibrations will not be tuned for specifically by any absorbing devices attached to the engine. It could lead to crankshaft fracture when stresses are high all around such as very high rpm. The state of being at a high RPM is a stress all in of itself- even if the engine is making negative horsepower and decelerating with no fuel going inside, it can still become broken at high rpm just due to the forces from RPM which can be tremendous after say 5800 to 7000rpm depending who you ask to define "high" as some engines see what, 13,000? 18k 30k 100k when is it "high"? Anyways- At some point those already annoying induced frequencies will resonate because an engine tries every single frequency as it moves from idle to redline often hitting key notes twice and thrice along the way. Resonance means the waves combine and result with higher output energy which can be absorbed and useful or extremely destructive. For example my school designed a jellyfish robot and they tuned the frequency of the robot swimming to resonate and maximize efficiency of the motion to conserve battery life, there is one or more ideal frequency for operation possible if the energy can be harnessed and absorbed by some mechanical or electrical signal. Limitations on the mechanical end are common- for example the engine intake manifold often resonates at 2200rpm then 5400rpm then again maybe somewhere in 9000rpm or 18000rpm and so forth. But only some of those rpm settings are available for the mechanical device.

2. If all cylinder show same or close enough compression, then do the pressure test at some point and fix all leaks, then connect the pcv system properly using PCV valve between intake manifold and crankcase, and a fresh air vent leading to pre-throttle body behind a quality air filter. Meanwhile, Install new cheap plugs copper TR6. Consider this a tune up stage. I would still run some sea foam on the old plugs though before putting in new ones. Clean the engine out best you can. Take off the intake and scrub what you can reach by hand with some brake cleaner if its not too much trouble. Get that thing as clean as possible and hook the PCV up and get a paper air filter (repeating myself because it is crucial to understand cleanliness and PCV before you can even think of performance, it will NOT perform properly when it is not clean and has a vacuum on the crankcase at all times). With no air leaks, a full pcv system, a clean intake manifold, a paper air filter (AFE sells high q paper re-usable washable) and equal compression, and new plugs, NOW you will drive it for 300 to 700 miles on a GOOD tune and then check the plugs. And they will all look identical and very clean because you will wear gloves when putting them in and taking them out (Disposable latex style gloves). Then you can put back in the iridiums (new ones) If you want because its good to go. And it will make the most power possible because all cyls will fire evenly and the crankcase sealed up (you pressure test the crankcase to 1psi or 2psi MAX to make sure IT doesn't leak just like the intake) and with PCV the rings will seal better giving you MAX compression and economy and efficiency. This is the key to success, PCV, paper air filter, pressure tests, even compression, new plugs on an already fully tuned engine.

[blindsquirrel]

A spread from 170 to 200 PSI is not going to cause a loss of one hundred (or more) foot-pounds of torque.

[kingtal0n]

A spread from 170 to 200 PSI is not going to cause a loss of one hundred (or more) foot-pounds of torque.

1. How do we know the engine is missing 100ft*lbs? Did he dyno somewhere I don't see?
Also how much torque it should make? There is no set number. It could be down 30, 50, 80, or 120 torque. We don't know how much is missing or why yet.

There is no way to tell if the engine is really missing 99 or 30 ft*lbs just by looking at a scanner log. I never look in those logs I have no idea what you see- it doesn't matter. Airmass calculations are ROUGH estimates. My scanner will tell me 68lb/hr of air when its making 500rwhp but there is no way my drivetrain is eating 180hp or that my injectors can flow 680hp worth of fuel. Bogus!


2. Every engine needs consistent compression and healthy clean cylinders NO MATTER WHAT. This has nothing to do with torque or power. It has to do with cleanliness and performance. Performance <> power. Performance is the overall application of our knowledge of internal combustion which includes efficiency and longevity, and diagnostic procedure. Torque and Power are third on the list, not first. You don't look for torque or power until an engine is healthy as health takes priority.


3. We could get an idea of how much torque it can make by fuel use, injector size, duty cycle, air fuel ratio, RPM. Is this what you are doing?
This would be available torque, not actual. And it is a tedious calculation (5 minutes- too much!) to make considering that it doesn't matter. The engine STILL needs to be healthy and cleaned up no matter how much torque it appears to be making. You can't gauge engine health by torque output. It could be running without an air filter materials and debris embedded to every scratching sliding surface, full of garbage and hard diamond like carbon deposits stuck to oil orifices and so forth, on its last leg and STILL make good torque. Torque <> healthy.



4. Just for fun lets see what sort of distribution we have,

170 or 180 to 208 is more than 15% across 3 or more cylinders.
So being conservative and locking our 15% constant for just 3 cyls,

366cid / 8 = 45cid~ per cyl.
15% of 45cid is 6cid from 3cylinders so,
366 - 18cid = 5.7L from 6L or roughly 6 to 7% reduction in torque overall
subtract another 5 to 7% for lack of dyno timed tuning and we could be over 15% short on torque
360CID lets call it 360ft to 400ft*lbs so 15% of that is 50 to 60 ft*lbs of missing torque
meaning the engine would only be making 300 to 350ft*lbs or so instead of 350 to 400 (down by 50 easily without good tuning and good compression)
At the tires this would be 350*0.86 = ~300torque to the tires Out of a potential near maximum of (400*0.86) = 344rwtq
Worst case is 250rwtq from a possible 360rwtq.

therefore I would suggest the engine could be down to 250 to 300rwtq from near max of 344 potential rwtq due to compression and tuning (fuel & timing) at this stage. As a wild, crazy, guesstimate that assumes nothing is wrong with any other part of the vehicle. Which we already know something is going on, since some of those plugs look like the injectors aren't spraying properly and one of them looks so trashed I wonder what happened to cause that.

[smokeshow]

I just can't with the endless walls of text 😂

[kingtal0n]

I just can't with the endless walls of text ��

This confuses me.
Average reader is 250WPM and I write < 1000 words per post so that is < 4 minutes of reading.


1000 words is nothing, a sparse summary

As to "endless wall" try reading Anatomy and physiology or General chemistry textbooks as a college freshman must,
General chemistry: "The average reader will spend 19 hours and 12 minutes reading this book at 250 WPM (words per minute)."

I hate to say it but it appears the majority of internet forum users are below a college freshman in reading ability.
And just because they got a degree doesn't mean they read the book properly or improved their ability. Many college graduates are still below freshman in terms of reading and other abilities.

[Frank_Castle]

Thanks for the wealth of information and prompt responses. I will work on tracking down the IAC wiring issue, run some seafoam through the engine, pick up a set of cheap plugs, and try to redo the compression testing when I get a chance.

[blindsquirrel]

Frank, I am sorry this happened to your thread. I am not engaging with that person up above any longer.

Sure I would like to see less spread between cylinders but that's not enough to cause your low power. Yes sure it would make more if every cylinder were 200PSI +/-0.001%. But if every cylinder tested 170 it still wouldn't be the issue here. If the cause was compression it would have to be bad enough on one or two cylinders you would have other, more obvious signs like smoke and oil consumption. It's not a compression issue, and your test readings back that up.

[2xLS1]

Every forum has one. This forum has a few.
OP, HP Tuners scanner is just that, a scanner. I would pay 0 attention to any torque numbers it displays. If you want to know somewhat accurate torque numbers, put it on a dyno.

[kingtal0n]

Every forum has one. This forum has a few.
OP, HP Tuners scanner is just that, a scanner. I would pay 0 attention to any torque numbers it displays. If you want to know somewhat accurate torque numbers, put it on a dyno.

Exactly, we don't know that there is any torque issue. I never said there was or even remotely suggested that there is. The difference in compression is a balance issue, a longevity issue, a long term problem to deal with immediately and not let it continue. And so forth (I show several possibilities for why it was different).

What I DID suggest is the appropriate method for fixing any potential issues regarding the cylinder seal, engine cleanliness, and explain thoroughly how to deal with the issues that appear on the plugs. And how to properly care for a performance engine (paper air filter and PCV system).

There is no superior method than what I outlined. There is no other way to go about fixing the various issues which is clear from looking at the plugs.

There is nobody on this forum or any other more qualified than myself to say these things. If you'd like a list of my credentials I would happy to share them but its another text wall and includes over 15 years of college course and 25 years of mechanical experience.

[smokeshow]

There is nobody on this forum or any other more qualified than myself to say these things. If you'd like a list of my credentials I would happy to share them but its another text wall and includes over 15 years of college course and 25 years of mechanical experience.

You sure bro lol

[DSteck]

Oh boy.