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Z

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While on the dyno today I noticed my EGT was only about 470C doing 4th and 5 gear pulls. I thought my probe has fried again (only 6 month old)...but it works fine as I drove home. I guess there wanst that much load on the car so the EGT wasnt the real world #?

Also, after mixing 50/50 race fuel, my EGT at idle as lowered considerably. 2 night ago when I drove back home I noticed my idled at 80C! I got scaed and drove my car around the garage and the EGT went back up, and then back down once the car stops....today while waiting to get my car on the dyno, EGT read
-40C! what the hell, eventhough its rainning and kinda windy today, will it lower my EGT that much?

any suggestions?

Jonas
 

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Zerosoul said:
While on the dyno today I noticed my EGT was only about 470C doing 4th and 5 gear pulls. I thought my probe has fried again (only 6 month old)...but it works fine as I drove home. I guess there wanst that much load on the car so the EGT wasnt the real world #?

Also, after mixing 50/50 race fuel, my EGT at idle as lowered considerably. 2 night ago when I drove back home I noticed my idled at 80C! I got scaed and drove my car around the garage and the EGT went back up, and then back down once the car stops....today while waiting to get my car on the dyno, EGT read
-40C! what the hell, eventhough its rainning and kinda windy today, will it lower my EGT that much?

any suggestions?

Jonas
Do you know exactly where your temp probe is located?
 
Z

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Discussion Starter #3
top of downpipe, just right after the exhaust manifold.
 

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EGT readings are relatively useless because there is so much variation from gauge to gauge, install to install, etc., so don't worry about them. If you want to know what's going on, buy a wideband. If you don't have a wideband, just hold a tight asshole and hope that everything is sort of okay with your A/F ratio, because that's all you can really do. :)
 

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I will probably make a mental note of my EGT's when I dyno with a wide band O2. When I get my a/f tuned if my EGT's are about 650c then I will set my warning meter on about 675c and not worry unless they exceed that #.

Later, Steve
 

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Steve,

IMO, that's about the best one can do with the GReddy/HKS/Apex type gauges -- try to use them as a sort of warning device to signal if something has gone off setting. The problem is that they're so slow to react that it's hard to make much real use of them. A pull through a single gear, as on a Dynojet, usually won't give them time to reach their peak reading. Then take into consideration that with all else being equal (engine load, RPM, throttle position, boost pressure, etc.) there is only 35 C difference between one full AFR point, and it makes it impossible to tune with any accuracy (I realise that you aren't trying to tune with EGT, but lots of other people think they can). AND take into consideration that AFR often changes for no good reason over time, even if you don't reset the ECU or fiddle with the fuel controller. I've seen two different cars in the past week do this very thing -- the AFR was carefully adjusted, then a few days later it was 2+ points LEAN -- DANGEROUSLY lean. Personally, I would not run a VPC without a built-in wideband. We haven't figured out what's causing the shift in AFR -- if it's the ECU, the VPC (most likely) or the fuel controller, but something is definitely happening, and left unchecked, it ain't good for reliability.

Steve

Steve Jarvis said:
I will probably make a mental note of my EGT's when I dyno with a wide band O2. When I get my a/f tuned if my EGT's are about 650c then I will set my warning meter on about 675c and not worry unless they exceed that #.

Later, Steve
 
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Discussion Starter #7
Boost Junkie said:
Steve,

IMO, that's about the best one can do with the GReddy/HKS/Apex type gauges -- try to use them as a sort of warning device to signal if something has gone off setting. The problem is that they're so slow to react that it's hard to make much real use of them. A pull through a single gear, as on a Dynojet, usually won't give them time to reach their peak reading. Then take into consideration that with all else being equal (engine load, RPM, throttle position, boost pressure, etc.) there is only 35 C difference between one full AFR point, and it makes it impossible to tune with any accuracy (I realise that you aren't trying to tune with EGT, but lots of other people think they can). AND take into consideration that AFR often changes for no good reason over time, even if you don't reset the ECU or fiddle with the fuel controller. I've seen two different cars in the past week do this very thing -- the AFR was carefully adjusted, then a few days later it was 2+ points LEAN -- DANGEROUSLY lean. Personally, I would not run a VPC without a built-in wideband. We haven't figured out what's causing the shift in AFR -- if it's the ECU, the VPC (most likely) or the fuel controller, but something is definitely happening, and left unchecked, it ain't good for reliability.

Steve

Boost Junky,
younds like you're the guy who can shed some light on my problems I have with my A/F ratio and EGT.
I've been getting high EGT for a while now, didnt really noticed before, so I decided to track down the problem. I replaced fuel pump, Fuel pressure regulator, and filter and installed HKS AFR to tun the A/F ratio. BTW I am BPU with FMIC, TTC mode.
coulpe of days ago I dynoed my car with wideband O2 and my A/F was 13.5:1, so we dialed 15% more fuel and got 13.1:1. however, seems like we cant go any lower than that even with substantial increase in fuel % (at 25% we lowered to 12.9:1) so we just lefted at 15% gain. Now my EGT gauge is by Omori, not the same as Greddy and HKs. it has digital readout and it reacts very quitely to temperature change. However, since you said every gauge measures differently, I'm beginning to wonder if my high EGT reading (760C at top end pull) really is just the gauge itself...becasue most of my EGT comparison is with Greddy and HKS EGt gauges.
what do you think?

thanx

Jonas
 

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Jonas,

I don't know for sure what is going on there. First of all, I'd make sure that ALL electrical connections, vacuum/pressure hoses, etc. are properly and tightly connected. Beyond that, it sounds to me like the AFR isn't doing its thing, OR the wideband isn't working accurately. If the wideband sensor is beginning to get fouled with lead (from previous runs on leaded gas) it'll just get sluggish -- it generally won't quit working or do anything that makes it obvious that it's crapped out. It can also get fouled with oil from an engine burning excessive oil (or blowing it by the turbo seals under high-boost conditions), and that can mess it up too. If possible, I'd try to put the car on another wideband and see what it says. If it tells you the same thing, I'd probably try removing the AFR and see what happens -- maybe try to temporarily replace it with another one or another model of fuel controller. I know that with my Field SFC, if I change the fuel by 2% at a given RPM, I can clearly see the difference in the AFR on the wideband. If I changed it by 15%, it'd probably make about 2 full A/F ratio point change -- for example, from 11:1 to 13:1 -- if not more.

IMO, all of the enclosed thermocouple type EGT sensors will have more or less the same reaction time. The fast ones are the enhanced RTD type, or the exposed thermocouple type, but practically no one uses those due either to cost or durability issues.

Sorry I can't be of more help, but these niggling little things are hard to diagnose without some trial and error. Maybe someone with some direct experience here will chime in...

Steve
 
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