240SX exhaust temperature

**kthomas** · 09-30-2006, 07:06 PM

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** · 10-01-2006, 09:07 AM

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** · 10-01-2006, 11:46 AM

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** · 10-01-2006, 12:03 PM

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

steve

**mgp240** · 10-01-2006, 05:27 PM

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** · 10-02-2006, 11:29 AM

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** · 10-02-2006, 05:13 PM

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** · 10-02-2006, 05:47 PM

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** · 10-02-2006, 08:08 PM

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** · 10-03-2006, 06:41 AM

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** · 10-03-2006, 11:16 AM

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** · 10-03-2006, 12:42 PM

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** · 10-03-2006, 01:36 PM

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** · 10-03-2006, 09:46 PM

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** · 10-05-2006, 07:55 AM

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** · 10-06-2006, 07:54 AM

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** · 10-06-2006, 09:47 AM

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** · 10-06-2006, 02:03 PM

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** · 10-06-2006, 07:52 PM

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** · 10-07-2006, 04:41 PM

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

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