240SX exhaust temperature

[mgp240]

Hi guys,
I was wondering if anyone out there can tell me what exhaust temp I should be seeing??
I have melted the #3 exhaust valve on 2 engines... the first was a stock motor with over 190k miles on it so I wasn't real concerned with it. But then in June I blew the same valve in a stock rebuild with only 5 race weekends and about 3-4 test days on it. I finally got another motor together and went to a test day 2 weeks ago and got some numbers...
I drilled a small hole in the #3 primary tube about 10 inches away from the head and hose-clamped a thermocouple into it. Recorded things with a Mychron 3.
I decided to see if I could get any change in temp by trying to trick the ecu (using a stock ecu from an automatic car) into putting more fuel into the cylinders by lowering the voltage reading it sees from the O2 sensor.
with the stock O2 hookup I got up to about 2000F in full throttle on the straights, with my modification installed it only dropped to 1950F and I cut the voltage going to the ecu down to 75% of normal, so it pretty much seems like my modification did nothing.
Any ideas? Are these temps normal? If so, what brand of valves are you guys using to withstand this?
Thanks,
Mike

[Eagle7]

I don't know much about boinger temps (rotary guy here), but I know they're lower than a rotary, and your 2000 degrees is way too high for a rotory.

Most (all?) ECUs ignore the O2 sensor at WOT, so messing with that signal isn't likely to gain you much. Sounds like you're running way too lean or your timing is way off. One of the best investments I ever made was a wideband O2 sensor so I can really see what AFR I'm getting.

Marty Doane

[lateapex911]

Right. Gotta get some real data there. I think 10" might be too close, and is elevating your numbers a bit, but even so, 2000 is too freakin high. Too bad you didn't get two sensors, so you could compare and contrast.

I'm a rotary /carb guy so I am NO expert here, but I would suspect a bad injector as well. Might want to either replace, or have them cleaned /tested. It's not something you want to screw up, as you've found out. Also, as mentioned above, timing will play a role as well.

[kthomas]

EGT should be measured about 6 inches from the port and be in the 1250 F to 1450 F range.

[mgp240]

EGT should be measured about 6 inches from the port and be in the 1250 F to 1450 F range.
[/b]
Only 6 inches into the exhaust piping???? Or are you saying 6 inches past the merge

I put it 10 inches down the pipe because I was interested in #3 so I installed it before the merge.
As for timing, I run about 12-15 BTDC(15 is factory)

[JamesB]

6" off the head is usually the recomended point for the thermocouple.

[Greg Amy]

WAY WICKED lean. No exhaust valve can stand up to those temps; hell, nickel alloys in a turbine would have a fun time with 2000F...

Sumpins' big-time wrong.

[MMiskoe]

As Marty said, the O2 sensor will have no effect on things at WOT. You might as well just unplug it.

If you can try cranking up on the fuel pressure instead. Sometimes fooling the ECU into thinking the engine is cold will help richen it up.

I'd also be looking for a manifold leak and trying the the thermocouple on the different cylinders to compare/contrast. At least a pyrometer on them to see if there are any wild swings.

6" from the head is similar to what I have seen on other motors.

Matt

[Ron Earp]

I'm in agreement - you've got a big issue. Therocouples are always installed around 6" out, planes, cars, etc. I've seen the same all over. 1400 would be nice to see, 2000F means you need to stop straight away - it won't last long at all.

The O2 sensors on cars are the transistion type crossing 1V output going rich to lean and visa versa. The ECU ignores the input anyhow at WOT as a couple have pointed out.

Get one of these:

http://www.aempower.com/ViewCategory.aspx?CategoryID=67

$250 on Ebay all day long. Have one for my Lightning, works well and just as good as higher priced ones.

You don't really need it though, you've got EGTs and that will tell you what you need to know - and it's telling you that you are extemely and dangerously lean.

Fuel pressure might help, but you might have some other issues at work with the injector being bad or something similar - no pulse signal to it, etc.

How are EGTs of other cylinders? If they are fine then you know you have a injector problem with this cylinder. If all are 2000F then you've got pressure and other issues.

R

[mgp240]

Well, the fuel pressure I know is good. I checked it when I installed the new motor. Will check it again of course and look into the injector and wiring first, as this seems like it would be easiest.
One thing I'm curious about... the 1400F ballpark figure, what type of driving conditions is that under? On track, dyno pull, tame street driving? I don't have the info in front of me now, but when I was off the throttle setting up for corners the temp dropped significantly and quickly (I want to say to somewhere around 1300, but I'll double check)
Thanks everybody for the help so far

[JamesB]

~1400 at WOT is ideal at any time, street and dyno are about the same quick bursts, and you know racing your WOT all the time. Without another cyl probed for comparison there is no way to tell if the FP is just too low overall or if its just a clogged/bad injector or a wiring issue.

[DavidM]

Just curious. How do you go about isolating which cylinder has an issue if you're using something like an o2 sensor? The sensor is usually plumbed after the exhaust pipes are combined so you're getting a combined reading. How do you tell which cylinder is lean if you get a lean reading? Based on this thread it looks like you could use an infrared pyrometer to check each exhaust pipe next to the port on the head and the one running hot is the culprit. Are there other methods? Just looking to gain some knowledge for future trouble shooting.

Thanks.

David

[stevel]

Just curious. How do you go about isolating which cylinder has an issue if you're using something like an o2 sensor? The sensor is usually plumbed after the exhaust pipes are combined so you're getting a combined reading. How do you tell which cylinder is lean if you get a lean reading? Based on this thread it looks like you could use an infrared pyrometer to check each exhaust pipe next to the port on the head and the one running hot is the culprit. Are there other methods? Just looking to gain some knowledge for future trouble shooting.

Thanks.

David
[/b]

Spark plugs are good thing to check for rich/lean conditions.

s

[mgp240]

Well, I checked the wire harness and injectors last night... Harness is good, all connectors fired the noid-light, after that I removed the fuel rail and zip-tied all the injectors into it and cranked the car over a few times with the injectors spraying into peanut-butter jars (real scientific, I know). All ammounts seemed close, but I have no real way of measuring. Then energized each one individually, and they all appeared to have a similar cone shaped flow, but again, no way of measuring the pattern or the small ammount of fuel that they shot. My uncle found a company that flow tests and cleans injectors, and I already have an email in to them to see what their turn-around time is.
Looking to check fuel pressure and run the ecu self-diagnostic on the injection system either tonight or tomorrow (I've run the diagnostics before for different problems and it has never helped me yet)
Again, thanks for all your input
Mike

[JeffYoung]

I know this sounds basic, but do you have a leaky head gasket maybe? Causing the lean condition?

[lateapex911]

Or a vacuum leak in that intake runner. Could be some weird valve that opens above idle, that sort of thing.

And the tesing of the injectors is a good start, but does it tell you what happens at higher and faster duty cycles?

One test would be to get a 2nd egt probe, and make a few runs, watching the pattern. No need to get close to 2000...then swap injectors...if the problem remains on that cyl, you know it's not the injector. You could probably do this on the street, no need to hit the track.

[Scott Nutter]

If it helps here is a graph of Mike's temperatures. Temperature is of course Channel_1. And I did the math so temp is in degF not degC.
[attachmentid=623]

[Eagle7]

...My uncle found a company that flow tests and cleans injectors, and I already have an email in to them to see what their turn-around time is...[/b]
I had very good luck with http://www.cruzinperformance.com

[mgp240]

OK, I've checked fuel pressure. Rock steady at idle at 44psi, when I rev and hold at about 2500rpm it dips very slightly (about 43psi) and comes back up to 44. WOT dips to about 42.5 and starts coming back up before I let off the throttle, and throttle response is very quick(it was sluggish and hard to start when I had a tired fuel pump that I changed out last spring)

http://www.cruzinperformance.com is who I have the email in to, so Eagle7's vote of confidence in them is reassuring, and the price looks good too... it's just a matter of how quick I'd be able to get them back.

I had compression numbers within 10psi of each other right around 180 when I installed the engine, so I don't think it is a head gasket thing. The valve thing is interesting... But I checked external temps on the header tubes with a contact pyrometer and got pretty close numbers for all 4 cylinders at idle. About 360F with the engine warmed up, which leads me to believe that all 4 cylinders would be running hot. Maybe it's just the fact that #3 is in the middle of the engine, so it fails because it can't get rid of the heat.

I talked to someone at Jim Wolf Technology and he said the stock injectors are 259cc, anyone know how much time they take to pass that ammount of fluid? He also said there is something seriously wrong with my engine and\or fuel system and that their computer would not compensate for it... you gotta at least appreciate his honesty!

I checked the fuel flow and I'm getting about 146 lph out of the fuel pump with no back pressure, but because the pressure doesn't drop significantly when I rev the engine, I am reluctant to attribute it to a low-flow problem from the pump.

Still floundering... any more ideas?
Thanks,
Mike

[ScottNutter]

Here's another problem...
according to the color of the plugs, I'm running rich
[attachmentid=624]
correct??
Mike

[kthomas]

Well that depends. Was this a good plug cut at rpm, or at idle? If idle, NFG. Was it unleaded fuel? If it was unleaded it will always look black. Is the instrument and thermocouple you're using properly calibrated?

[mgp240]

I run unleaded premium.
The plugs have the one test day I got the temp info from and about 15-20 minutes worth of revving in the garage.
As for calibration... officially no, but I hooked up a temp controller from work to the same TC and got the same numbers in the garage as I did on the Mychron, I didn't try multiple TC's though. Even uncalibrated, I can't see a 600F error.

Mike

[lateapex31]

I talked to someone at Jim Wolf Technology and he said the stock injectors are 259cc, anyone know how much time they take to pass that ammount of fluid? He also said there is something seriously wrong with my engine and\or fuel system and that their computer would not compensate for it... you gotta at least appreciate his honesty!

[/b]


Injecotrs are rated at 3 bar fuel pressure. So your 259cc injectors, at 3 bar, should flow 259cc in one minute.

Have you put a wideband 02 sensor in the car to see if it is overall rich or lean? What about a bad crank or cam angle sensor which would cause the ECU to retard timing (which would make the EGTs look very hot)?

[stevel]

What's the state of the entire fuel system? On the SOHC cars just as a rule of thumb we now just replace the fuel pump, have the injectors cleaned and rebuilt, replace the fuel pressure gauge and change the fuel filter. If you don't know, I would just replace them all. Because at some point you're going to be chasing that problem for a while. You'll have a complete failure in one, replace it and get that fixed and next thing you know you're chasing the next weak link because it fails. You'll save yourself a lot of time and hassle to just replace the whole fuel system at once. That way you can rule out the fuel system as part of the problem for the lean/rich condition and start looking at spark, ecu, etc. We learned that the hard way. Then make sure the ignition system is up to par. We've had a lot of problems with distributors on those cars because of it's proximity to the header. If your header isn't wrapped or have some thermal coating you will cook the distributor and it usually happens on track leading to wacky timing and results in a blown motor. Replace spark plugs, wires, cap and rotor if you don't know the condition of those either. I hate throwing money at problems, but if all of those things are suspect as far as age/condition they will fail and it will just cause headaches. You need to be on top of maintenance with these cars or bad things will happen. They're not as bullet proof as say the hondas or mazdas, at least IMHO and experience with them.

Good luck.

Edit: Here's a good post of all things to go thru.
http://itforum.improvedtouring.com/forums/...indpost&p=64511 (http://itforum.improvedtouring.com/forums/index.php?s=&showtopic=6499&view=findpost&p=64511)

steve

[mgp240]

OK, here's the latest...
at 44psi (very close to 3bar), 55F, and 20 second spray all 4 injectors passed 3oz of gas... 9oz/min equates to 266cc/min. so even with my crude measuring, I at least know all injectors are close to each other and they are also close to the 259cc spec.

MAF sensor is giving propper voltage, and the harness from MAF to ECU is good, so the ECU is geting the signal

fuel pump is about 1.5 years old. new filter installed with engine
cap rotor and wires were replaced before my last race and plugs that I posted a pic of were new before the test day. all 4 plugs give a bright pulse with timing light, and timing is steady at idle. timing is also steady when car is revved up and held at a steady rpm. I am running an msd blaster coil (1year old) with stock control module.

does anybody run a plug with a different heat rating than a stock plug? I am currently using Denso's that are listed for the engine. should I be using different ones?

Mike

[AntonioGG]

I think you have unmettered air getting in from somewhere (pending a test of different cylinders to see if it's the same everywhere).

If you cover the intake at idle, will the car keep running?

[DavidM]

Rebello specifies a specific Champion plug for their engines. I'll have to look up the specific number when I get home. This is with race gas.

I would think an air leak would cause a stumble at idle and/or during acceleration. At least that's the experience I've had with cracked throttle body boots on other cars. You could do the ole put some rubber tubing to your ear and listen around the intake manifold and boots to verify.

You could get an el cheapo O2 meter to verify the lean/rich condition at idle and during acceleration.

David

[seckerich]

For much less than the cost of throwing parts at it you could take it to one of the dyno's in town and do a base pull with the sniffer and see where you are at. If you weld in the O2 sensor fitting most of them have a wideband setup you can use. Would be less than $200.00 and might even find some power to boot. Good luck.

[lateapex911]

If you suspect an intake leak, spray some carb cleaner around the suspected areas, and if indeed there is a leak, the rpms will surge.

[CCARVER]

If you suspect an intake leak, spray some carb cleaner around the suspected areas, and if indeed there is a leak, the rpms will surge.
[/b]
This will work great for the air leak. But if you have had both an air leak and a bad plug wire you will get a fire ball. Shortly after the fire ball you will be in my current condition, bump on the back of the head and no eye brows for a couple of weeks.
let us know what you end up with. I love chasing down stupid problems.
Carver

[mgp240]

I've always use a propane bottle for detection of vacuum leaks. I did that and still have my eyebrows, so no leak.

I was considering getting a cheap O2 gauge, but decided I could just use a multimeter in the garage. The factory manual says its a sharp drop in voltage from rich to lean 1-0 volts, but I don't think so... the analog gauges for sale have evenly marked faceplates and say that they work with "OEM style 0-1volt O2 sensors" From everything I can tell 17:1 = 0v, 16:1 =.2v, 15:1 = .4v, 14:1 = .6v, 13:1 = .8v, and 12:1 = 1v
so I should read about .9v off of the O2 sensor. When I was "conditioning" the signal (see earlier posts) I was getting .85v at idle, and I decreased it to .65v going to the ECU. I never bothered to get higher rmp readings... that's next.

Anybody have a dyno shop in northeast OH or western PA that they recommend?

Thanks,
Mike

[lateapex911]

This will work great for the air leak. But if you have had both an air leak and a bad plug wire you will get a fire ball. Shortly after the fire ball you will be in my current condition, bump on the back of the head and no eye brows for a couple of weeks.
let us know what you end up with. I love chasing down stupid problems.
Carver
[/b]


Chris, don't you watch TV??? SAFETY glasses my friend!

Oh...use the little tube that comes on the can so you can stand further back.

It's not always what you do in life, but HOW you do it! ;)

[CCARVER]

Chris, don't you watch TV??? SAFETY glasses my friend!

Oh...use the little tube that comes on the can so you can stand further back.

It's not always what you do in life, but HOW you do it! ;)
[/b]
Well my safety glasses have a nice colored tint to them now.
And not knowing that my codriver just hosed everything down with brake cleaner before the air leak hunt.
So not a bad method, just not one to share with someone.
Do it alone when you are in control of the variables.

DYNO is the way to go. Then you will have base numbers and should be able to find your problem with ease.
Carver

[charrbq]

I wondered why you weren't at the meeting tonight. I never had a chance to ask John if you guys were going to make it this weekend. Hope so. I keep finding problems with the car that I didn't know existed, but Gary and I should be there both Friday and Saturday. No way on Sunday. It's only been 12 weeks since the surgery, and I'm pushing it.

[mgp240]

I'm going to the dyno after work tonight. doing the standard 3-pull average to get a baseline. Also going to get AFR and I'm going to ask if they have a thermocouple input to record #3 EGT.
I'll post results

Mike

[mgp240]

Well, low fuel ammount is definitely not my problem...
at full throttle I was low 12's to high 11's
HP numbers were lower than I expected, but it's not running right. HP 126.3, torque 137.5
we did 2 pulls in 4th gear, then one in 3rd to make sure that there was still enough fuel when the rpm raised faster.
Dyno guy told me to try: advancing timing, go to a colder plug, or colder thermostat
so... back to searching
Mike
[attachmentid=626]

[stevel]

Dyno guy told me to try: advancing timing, go to a colder plug, or colder thermostat
so... back to searching
[/b]

I think it's something more than that. Like you said it's not running right but it's not gonna get fixed by a different plug or advancing timing. A stock plug and stock timing should be putting down more than that with a better A/F. Check again the whole fuel sytem and make sure everything to do with spark is working. Do you have a spare distributor? Might be something to try there. For some reason it's either getting too much fuel or it's not burning off the fuel it's getting.

I would look for vacuum leaks. The inake tract (you still running the stock rubber intake? check it for cracks), the intake manifold gasket (both the upper and lower), at the MAF and TB.

s

[DavidM]

Were you still seeing the hot exhaust temps? What does your exhaust system look like? Stock header? Stock piping back to the muffler? Could it be that your exhaust system is too restrictive causing backpressure and heat buildup at higher RPMs? These cars like to breathe at higher RPMs. I've got a custom header with 3" pipe all the way back. May be a long shot, but when you've checked the usual stuff it's time to look for the unusual.

David

[mgp240]

I didn't get the exhaust temps during the dyno runs... didn't have time to get the mychron out of my uncles car.
I plan on getting a few rev runs in the garage with the different plugs and different timing, and see about temps.
I am running a pacesetter header into 2.5" through a Summit straight-thru muffler(where the Cat used to be), and then 2.25 pipe the rest of the way back.
MAF is good, Injen intake, no leaks anywhere

[backformore]

Going back to the probe position, does anyone have any idea how much of a difference the location makes? I've had high readings on the VW I bought, but the probe is no more than 4" from the head. I just wonder if my high readings could be a result of that.

I am going to watch this thread intently since I am seeing similar problems on the VW. It will be a while before I can get it to the dyno (just found the broken tranny input shaft this morning), but sheets from the previous owner did not show a seriously lean condition, in fact mostly 13.5 - 14.2.

Thanks

[Eagle7]

I didn't get the exhaust temps during the dyno runs... didn't have time to get the mychron out of my uncles car.
I plan on getting a few rev runs in the garage with the different plugs and different timing, and see about temps.
I am running a pacesetter header into 2.5" through a Summit straight-thru muffler(where the Cat used to be), and then 2.25 pipe the rest of the way back.
MAF is good, Injen intake, no leaks anywhere
[/b]
If you really have 2K degree exhaust your header will be cherry red - very clearly noticable.

I've forgotten, did you check the other runners? How do they compare?

[mgp240]

Other tubes read within 100F
I am looking into the readings though, I'm not sure what TC the mychron is set up to take as an input... (I don't think the difference would be a 500F one)
After a race they header is slightly red, but not glowing (carbon steel melts at ~2600F ??)
Mike

[kthomas]

Headers will look normal after a race, and during operation at part throttle. Only at WOT or heavy load will they be bright red/orange. They will return to a normal color within seconds of the throttle being lifted. If your headers are still red after a race, you got real problems.

[Ron Earp]

Is there any malfunction on this particular car that could cause the spark in this one cylinder to be severely retarded? This would cause a lot of heat and can easily burn an exhaust valve.

Clearly if it uses a dizzy this would not be possible since it'd affect all cylinders the same. But could it be possible with a crank fired ignition system? Just a stab in the dark here as not much is adding up here.

Ron

[slickS14]

I would also think ignition timing with header primaries being "red" or fuel pump not keeping up under load at RPMs. Check your wiring/ground/connections to the pump because that can greatly affect the pump operation as well. Something else worth checking is your camshaft timing components. If the oil pressure activated chain tensioner is not working properly it will be changing your cam timing at different RPMs which in turn changes your combustion/fuel/spark/power...just a thought. I had a chain tensioner blow a plug out that looks similar to a freeze plug once and experienced similar problems. I had fun trying to diagnose until I went to the dyno chasing other ideas and found the problem. I bought a new one from Nissan and had the plug tig welded in place and have had no more issues. Ofcourse I fished the old plug out of the oil pan.... Good Luck. Your best bet is to make friends with a dyno owner!

[mgp240]

I'm not sure what TC the mychron is set up to take as an input... (I don't think the difference would be a 500F one)
[/b]
Well, with the propper TC (purchased from Pegasus, and made by Aim Sports) the temps are in the 1300F range 6 inches from the head at 5k rpm no-load rev for about 1 minute in the garage. So, in a way, I was right... it wasn't a 500F difference... it was a 700F difference. After all that fiasco I may have finally learned to purchase the correct tools and parts for the job instead of trying to make do with what's around (but probably not... look at the signature)
Now the real issue. I started looking into this because I blew a relatively young engine up in the same way that I had blown up a junkyard motor the year before.
I still have NO IDEA why I would be breaking/melting #3 exhaust valve!
I'll be racing this weekend with the mychron installed, so maybe I'll find something then.
Thanks for all your help... even though it turned out that my exhaust is running normal temps, I still got quite a bit of useful info from this thread.

Mike

[John Herman]

...I still have NO IDEA why I would be breaking/melting #3 exhaust valve! ...
[/b]
Now that the temp thing is resolved. The likely culprit is valve float. The fact it was the same cylinder could be dumb luck (1 in 4). First, any over reving? Be honest. Over reving on downshifts is easy to do. Get a memory tach to check yourself. Second, if the head was redone, the valves moved up into the head, reducing the preload on the springs. So, you need to be sure your head is setup correctly. First, use new springs and have them checked for preload, or inspect your used springs CAREFULLY and have them checked for the correct load at installed height (the value should be in the service manual, something like 85# @ 1.5" for example only as I don't know about your engine specifically.) Then check the installed height of ALL the springs in the cylinder head. You'd be surprised how far off they will be (.010-.035" depending on how old the head was or how aggressive the machine shop was). If the preload is not correct, you are losing rpm capability on your engine. Check for any "bad" lifters, (cracks, scores). Once that is set, another thing to look at is oil viscosity. Don't run too low of one, or get too fancy at this point. When I went to the 30W Redline oil (and I actually tried 40W and their blends as well), I started having all kinds of problems. I now use Mobil One Delvac 15W-45 (the stuff for diesels). I've heard Rotella is very good as well. If you're worried about dino oil, change it every weekend. The reason for the oil concern is you could be aerating the oil, which messes with the lifters, causing them to bleed down and "drop" the valves onto the seats. (Sort of like getting air in your brake lines.) Also, make sure your windage tray/oil pan are up to snuff to eliminate oil pickup/aeration problems. I never found an Accusump was effective enough for me to band-aid the issues. Once I fixed all this, my valve problems significantly reduced. Good luck. This is a frustrating and EXPENSIVE problem to have....I know.

[mgp240]

As for the over-rev... the first engine, yes. The recent blow up, I didn't over-rev. I had the light set to 6100, and it usually comes on between 6000 and 6100. I also found out that my tach is actually reading a little high from the dyno and the mychron. (tach reads 6100, actually 5950)
I have pics of the head and block from the June disaster... here is the head pic, reduced enough to fit it on here.

[attachmentid=649]

[Eagle7]

Wow!