R33 GTR AFR levels at cold start, cruising and WOT....please help

[judasentinel]

Just wondering if someone can confirm if there is an issue with my car or if this is normal...

Cold start, the idle is at 16.5-17.9....and then it very very slowly (after about 5-10 minutes of idling) comes down to around 15.5-16, and thats where it stays.

If I try to rev the engine during this time, the AFRs jump off the chart - fuel cut off, going above 18 on my AEM gauge.

Partial throttle cruising, AFRs are either below 14.7 or above 15.0

WOT AFR is around 12.

Stock ECU, no major upgrades, stock injectors, LS2 coils. Not sure if the above is normal or if something is amiss.

Hope someone can chime in and help.

Thanks

[Bruizer]

you have broken gtr horseshoes in your butt for years

[judasentinel]

You're such an inbred., haha...

Doesn't look like your head injury ever healed. I might have horseshoes up my butt, but you sir, must have the rest of the horse up yours. Why don't you move to the Church & Wellesley area in Toronto? You will fit right in...no wait, all the guys there will fit right into YOU.

Don't ever stop wearing your helmet when you ride the short bus.

The above was joke...pls don't take it seriously and jump off a cliff in depression. And if you are offended, its your problem.

[caliber676]

If I'm not mistaken the wot and cruising speeds are pretty normal but the idle and cold start numbers look a little lean. I would look at the throttle linkage adjustment and the iacv aacv adjustments and function.

[judasentinel]

Thank you for your response.

The car continues to have fuel cut from 2300-3000 rpm. I see the AFR jump off the charts to over 18 but only in that rpm range. I am certain the ECU is stock, and no chips have been installed in it. Is there a causal relationship between that rpm range and the AFR going over 18?

Since the rpm range seems similar to that during which we encounter the MAF errors, I am thinking that perhaps this is related to MAFs? I have checked the solders and the filament in both and it seems fine. Is there a way to test the MAF itself to see if it is registering the correct voltage for the corresponding airflow?

[caliber676]

The only way to test mafs other than power going in and grounds is using an oscilloscope to scope the voltage pattern

[judasentinel]

Just came back from a 200 mile road trip....the car boosted great, but half way through the trip, it started running like a Subaru when idling....the AFRs dropped to around 11-13 while cruising and on WOPT would jump to over 13 at times. When I got home, the idle was a bit rough, not that bad, but I could feel something was amiss, so I decided to check the MAFs.

While the car was idling, I disconnected the rear MAF, and revved the engine, and it revved without any problems to over 4000 rpm, even though the rear MAF plug was disconnected. I plugged it back in, the revs dropped a little bit and then stabilized. Then I disconnected the front MAF and revved the engine and it wouldnt rev past 2500 rpm. Plugged it back in and it revved ok. Is it normal for a GTR to limit revving to 2500 rpm when the front MAF is disconnected but rev normally with the rear MAF disconnected? Incidentally, it is also the rear MAF that gets the oil splattered into it.

This has me perplexed, as I was under the impression that either MAF when disconnected would cause the revs to not go past 2500 rpm, and not just the front one. If this is normal, I can breathe a sigh of relief. I will swap the MAFs out tomorrow and do this test again in the morning to see if the issue moves to the front plug or stays with the rear plug. I will also hopefully be able to resolder the MAFs soon, and maybe that will help.

If someone knows of this issue (that I described above), please do share. Thank you.

Maybe I should go back to the BKR7Es that I have. Let's just hope that this has nothing to do with the LS2 coil swap that I have done, as the car does seem to have more grunt than before.

[judasentinel]

Update:

I just resoldered the MAF, cleaned all the plugs and guess what I found - plug no. 5 was completely fouled. I checked all the LS2 coils and they are all firing, but for some reason, there is little combustion happening in cylinder no. 5. Put a newer plug into it and still nothing. I thought maybe coil no. 5 was bad, so I replaced it with a spare I had, and still the same result. The car has a minor shudder, very minor, with the wideband saying it is running 14.7-15 AFR, and when I rev it, the car misfires. Definitely something is up with either the quality of the current that it is not burning the fuel up completely or I have lost cylinder 5.

What are the signs of a blown cylinder? I am a bit freaked out here, because I can see the coils sparking, but I cannot tell if the spark is of equal strength across all cylinders or if no 5 has a weaker spark. Please help as I need to get the car fixed before storing it next month.

Thank you.

[judasentinel]

Just checked compression. 70 psi in cylinder 5.


The plug was wet with gas and a bit of oil.

I drove the car to a shop and it drove mostly ok after warming up, even with this low compression. Injector was firing, and so were the coils. Seems either rings/pistons or the top end is messed up - could be a partially stuck valve/lifter/ faulty spring, or do you guys think it is the bottom-end?

My only recourse is to have remove the head and take a look to see what is messing it up.

[future_R34]

R33 GTR AFR levels at cold start, cruising and WOT....please help

You tried compression or a leak down test? If you have an air compressor, just get something to screw an air line to your cylinder(like a compression tester hose) and blow in air(~5psi should be plenty) when it's at TDC. If air is leaking out exhaust you might have a bummed valve. If you get air In the intake side, that valve...or case vent then it's bad piston rings...wouldn't drive it until you get it sorted, as to not damage it further

[judasentinel]

It would be quite difficult to get cyliner no.5 to get to TDC....maybe stick a metal rod in there and let is come up until it reaches the top? Are both intake and exhaust valves supposed to be closed at TDC?

The car is at a shop and the mechanic says that it is impossible to do a leakdown test and know for sure, since he doesnt know where the compression leak is. My take was that since there is no fuel or coolant mixed into the oil (checking the dipstick), there might not be an issue with the piston, but then I wonder if there was valve issue (intake or exhaust), the cylinder would not hold pressure....the mechanic said that his compression tester didnt hold pressure - it simply recorded on the dial and then a valve just kept the gauge in that spot.

Does that add up?

I have always thought that a blown cylinder would not allow the car to run at all, or the idle would be extremely rough. In my situation, the car idled fine after warming, with a slight shudder. It did take its own time to warm up, but the AFRs were stable at around 15 while idling, and the power was still there when I drove her to the mechanic. Could this be a case of something just slightly stuck?

I have read on the Sky Life that if you drop a little bit of oil inside the combustion chamber and let it coat the piston and then do a leakdown test or even a compression test, the results should come out higher if it is the bottom end, and if the compression is still low with the oil having coated the piston/cylinder walls, there is something amiss with the top end. Anybody want to confirm that logic?

Here is the link to it: http://www.skylife4ever.com/2011/01/compression-test.html

[Bruizer]

The teaspoon of oil in the plug hole is often used to confirm if it's a ring but it's sometimes vague but yeah if the value improves then it's a ring. You could have bad compression and not notice much when idling or driving. A borescope is good to take a peek at a piston and see if maybe a valve struck a piston and bent but I'd expect to see most do the same, not just 1. In many cases 1 low reading is rings... but I don't think there's a way to test the valves without simply looking at them with the head off.

[future_R34]

If you pull off the valve covers, get a brass drift and soft face hammer, then smack the #5 exhaust and intake valves(this sometimes help seat valves if there is carbon build up etc) Then try compression test again. If your mechanic isn't seeing any compression on gauge than you most likely have a valve issue.

If rings were bad you would have low compression. Sounds like valves may not be seating properly, causing the zero reading, but while running and after warm up its not as bad due to expansion.

To get TDC for number 5 cylinder( all 4 valves should be closed) there's a quick trick. Pull all the plugs except for #5, turn engine with your hands and at some point you should start to feel that piston on the compression stroke(getting hard to turn). When you get to that point pull out the spark plug and look down at the piston and you should be able to turn engine slightly to get it to TDC.

[judasentinel]

Thank you, Bruizer and future_R34.

There is compression in cylinder 5 - 60 to maybe 70 psi as the mechanic told me, and this was after running and driving for 10 minutes to get to him. I think it was 60 actually. When I looked at the gauge, it showed 60 psi and the needle stayed there. When I asked him about it, he said that his gauge has some kind of a valve that keeps the needle where it is supposed to be, even if compression drops to zero, to be able to record the max compression the gauge registered. Not sure about that explanation, but maybe a compression gauge can hold compression number in place....but then how does one know if it would drop, to rule out the bottom end? Does compression build up to 60 psi and then drop off to zero? I didnt see it go down to nothing.

I say that the fact the the compression did build up to even 60 psi, means that there is some kind of a sealing happening, and the rest is escaping. If there was an issue with a valve, the gauge wouldn't register anything as all gases would escape out the leak.

So this might mean rings? He does intend to take the valve covers off and look into the top end and if he can find the cause, he will try to fix it. Otherwise, he says the head might need to come off to find out what the situation with the valves is, and the headgasket. And if the head and valves look fine, then the engine needs to come out to fix the ring issue.

People swear by this thing called Restore, which seems to seal off ring-related compression issues within a few hundred miles. The company claims that it WILL FIX those issues, unless there is physical breakage in the rings, or if the piston has a hole. I am just hoping that worse comes to worst, a rubber mallet fixes the problem.

[GTRADDICT]

Take cam cover off. Take all plugs off except 5. Take a screw driver in spark plug hole and get piston to tdc. Shoot some air in the bitch and wait. If all is good you sir have a dead piston ring. Do a dry and wet comp test. If the wet is really higher you have a dead piston ring.
Good luck

Edit: after reader your other threads, I'm assuming cyl 5 is powering the rear turbo and you have oil near that turbo. I bet the oil is coming from your bummed rings... Or a really bad valve seal... but you have to do some testing before.