1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

High EGTs Under Load

Discussion in '80-Series Tech' started by Scamper, Dec 14, 2003.

  1. Scamper

    Scamper

    Messages:
    1,460
    Likes Received:
    2
    Joined:
    Mar 28, 2003
    Location:
    Somewhere in NJ
    I'm looking for help in diagnosing high EGTs on a S/C engine only when under load. Here's the scoop:

    Normally, during the summer, my EGTs under load with a trailer in tow runs between 1300 and 1425 F (max) when going up 5-8% grades at 65-75mph. I've noticed that the EGTs I'm seeing now are running 1300-1450 under mild loads without a tow at the same speed or less, and with temperatures significantly lower than during the summer.

    On flat grades, I used to run just under 1200...now run just over 1200. So the difference here is not much, expect that I would have expecte somewhat of a lower temp due to ambient temperatures.

    The "problem" seems to be noticable only when really under load.

    Initiall thoughts are:
    1) lean-run condition leading to high EGTs...why? Fuel filter is less than 1yo. Regulator?
    2) dirty air filter leading to constricted air flow (should not result in lean condition due to ECU and MAF correction?). Beats me.

    I'm conflicted here.... I do not know enough about the LC computer and just what would cause a S/C engine to run high EGTs. I can see reasons why both a rich or lean condition would lead to high EGTs, but it always ends up being something the ECU or MAF should correct for if I understand it right... ???

    If you have any idea or (preferably) knowledege of why this would happen, please let me know...

    Tom
     
  2. ppc

    ppc M Go Blue

    Messages:
    1,796
    Likes Received:
    406
    Joined:
    Aug 18, 2003
    Location:
    Nashville, TN
    I'm not sure what they do in NJ for winter months but in several parts of the country there are winter formulations for fuel. This may account for the change. You might just want to try and toss in some octane boost to see what happens. Another thing to look at might be the various temp sensors on the engine. You may also want to hook up a volt meter to the O2 sensors pins in the DLC and monitor there output.
     
  3. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

    Messages:
    21,641
    Likes Received:
    5,035
    Joined:
    Mar 27, 2003
    Location:
    Surrounded by Cruisers from all over the world
    I agree with Phil.

    Around here they add oxygenators to the fuel in the winter. I do not have a pyrometer to confirm but I imagine that an additive like that could increase combustion temps.

    Is this your first winter with the gauge?


    D-
     
  4. Scamper

    Scamper

    Messages:
    1,460
    Likes Received:
    2
    Joined:
    Mar 28, 2003
    Location:
    Somewhere in NJ
    I had the gauge on last winter too, but didn't notice this sort of behavior. Other than the high temps, it runs fine. I'm just a tad worried about going "too" high, whatever that may be.

    They do add MTBE here in Joisey. And, BTW, the coolant temp is just peachy, though you'd have to really heat things up I think to affect that.

    I had wondered about the O2 sensor(s) but thought that if they were bad, then the problem would be exhibited across the board, and not just when under load. At idle, it behaves just as I would expect--700 F +/- and in summer about 800 F (ambient temperatures alone would make up for most of that difference).

    So from what I'm hearing, this is nothing to be concerned with?

    Thanks,
    Tom
     
  5. BigMac

    BigMac SILVER Star

    Messages:
    216
    Likes Received:
    0
    Joined:
    Mar 27, 2003
    Location:
    Lompoc, CA
    Tom:
    I have seen EGT temps well above yours in all operating regimes since I installed the S/C last summer. I try to back off the throttle to keep it at 1500 on long hills, but I have seen 1575 worst case. I haven't had time to get an OBDII reader yet to see if I can correlate O2 sensor condition or anything else that it might show. BigMac
     
  6. krich97

    krich97

    Messages:
    90
    Likes Received:
    0
    Joined:
    Dec 3, 2003
    OK, so I had a check engine light, went out to buy a scanner, ended up getting a code reader - but it did come with a fairly informative manual. My code was a PO401 which means a prob with my EGR - not enough (if any) of the unburned exhaust gasses being rerouted back into the combustion process. Why does this matter? ???- Well according to the manual one of the main reasons exhaust gas is recirculated and included with the air/fuel mixture is that it lowers the combustion temperature by up to 500 degrees! (This is done to reduce the formation of certain types of hazardous compounds which occurs above 2500 deg f and to protect the cat) Anyway, in addition to winter fuels which are often oxygenated, if there was any reduction in recirculated exhaust gasses (perhaps also because the exhaust % relative to a S/C engine's higher fuel and air use under load may be reduced) the result would be somewhat higher combustion and exhaust temps. A hose could have restricted flow etc. I guess if engine and coolant temps are not elevated, you are in the normal temp range, and you don't have a check engine light on, I would think it should not be much of a problem although it might wear out the cat faster.
     
  7. ppc

    ppc M Go Blue

    Messages:
    1,796
    Likes Received:
    406
    Joined:
    Aug 18, 2003
    Location:
    Nashville, TN
    Tom,

    Exactly where is your probe located for the EGT? It could be possible that the probe itself might be failing or aging. Mine is located real close the location of the O2 sensors on my 94. Well down stream of the highest heat coming out of the head. I been told that the sensors do "wear" from heat but that has been from guys that have turbos with the probes located very close to the output of the turbo.

    I'm of the belief that the ambient temperature has very little impact on EGT under load. When pushed in similar conditions to what you’re describing while towing I see EGT readings of 1500 regularly. Granted I haven’t towed for a couple of months now that it is not boating weather.

    I would keep an eye on things but for the present time not be too concerned.

    In the past week I’ve been running without the supercharger (no belt, don’t ask) seems to run fine, no power, but I can’t get the EGT up over 1300 pushing it at 80 mph either. I’ve got to force the bypass open to see what happens.
     
  8. Scamper

    Scamper

    Messages:
    1,460
    Likes Received:
    2
    Joined:
    Mar 28, 2003
    Location:
    Somewhere in NJ
    Thanks guys. I guess I'll take a close look at my EGR system to see if there might be anything askew, but I think you're right--I'd get a code if that were the case.

    Phil: you've "disabled" the S/C by just removing the belt?! I didn't know that could be done...I always thought that the roots blower would restrict the air flow into the engine if you did that. Does it run "normally" when you do this? If so, I'd be tempted to do it for a while just to get a good baseline on the EGTs. What did you mean by forcing the bypass open?

    Tom
     
  9. Gumby

    Gumby Supamod Staff Member s-Moderator

    Messages:
    11,977
    Likes Received:
    415
    Joined:
    Dec 13, 2002
    Location:
    Knee deep in hookers and gin
    You will throw a P0401 code if your EGR is not working. The system is very sensitive. I suspect it is a fuel issue. 2500* is the magic number for flame temps because it is when NOX emissions happen.
     
  10. sjcruiser

    sjcruiser

    Messages:
    834
    Likes Received:
    3
    Joined:
    Apr 3, 2003
    Tom,

    Insufficient air flow or a tired fan clutch would be the cause as well (sorry if you've already considered this).

    I'd try to blow out the craps on radiator and ATF cooler fins first.

    Regards,
    Frank.
     
  11. Scamper

    Scamper

    Messages:
    1,460
    Likes Received:
    2
    Joined:
    Mar 28, 2003
    Location:
    Somewhere in NJ
    Todd,

    Thanks for the info on the MIL. Maybe you or someone else can explain something else to me...

    If I'm running either rich or lean--both of which could result in higher temps--wouldn't the O2 sensors pick this up, report it back to the ECU and adjust the mixture automatically to compensate?

    I started to think that my air filter may have been clogged, causing a lean burn, but I can't logically get past the fact that the ECU, O2 sensors, and MAF are supposed to correct for all this. What am I missing here ??? ?

    Frank,

    Thanks for the suggestions, but the cooling system is running fine. It's the exhaust gas temps I'm seeing higher than expected.

    Tom :beer:
     
  12. krich97

    krich97

    Messages:
    90
    Likes Received:
    0
    Joined:
    Dec 3, 2003
    Tom, I could be wrong but a clogged airfilter should produce a rich (too much fuel vs air) condition not a lean condition (too much air vs fuel). As you said, I would think the computer would correct for this. A lean condition would result in higher combustion temps but less emissions (less unburnt fuel) and probably higher exhaust temps at the point you are measuring them. I do not understand how a rich condition would produce higher combustion temps but maybe there could be some late burning of unburnt fuel in the exhaust which could raise exhaust temps (I am just guessing). It definitely makes sense that a S/C engine could have higher exhaust temps than a non S/C. There is more air and fuel in the combustion chamber and correspondingly there are higher pressures and possibly temps (more power and more heat is being released during each power stroke) As for the fact that you used to run cooler - I would think fuel composition would be more important than ambient temperature - Oxygenated gas supposedly produces somewhat less power but may actually burn a little leaner and hotter (if not corrected for by ecu etc)
    For fun you could spray some ether or starter fluid into the intake while running around 2000 rpm and watch what readings you got from the exhaust temp and O2 sensors.
     
  13. Gumby

    Gumby Supamod Staff Member s-Moderator

    Messages:
    11,977
    Likes Received:
    415
    Joined:
    Dec 13, 2002
    Location:
    Knee deep in hookers and gin
    Rich mixture will cause the combusion temps to go down. A clogged air filter will be compensated by the MAF anyway. A leak between the MAF and the throttle would cause a lean run condition, but the O2 would try to compensate. It would also cause other drivability issues.
    The ECU will absolutely compensate for too rich or lean conditions if it can. If it can't, it will turn on the MIL and set a code.
    I like the EGR not working to cause the high temps. It might have been at a time when the EGR monitors were not on and the ECM didn't catch it. I also like the fuel issue, especially if it doesn't repeat with the next tank.

    Krich97 is right. A clogged filter would cause a rich condition on a carbed or speed density system, but not on a mass air flow. Lean burn would raise combustion temps and lower HCs but would raise NOX emissions. Rich conditions might cause the cats to get hot, but not really the exhaust unless the sensor is very near the cats.
     
  14. Scamper

    Scamper

    Messages:
    1,460
    Likes Received:
    2
    Joined:
    Mar 28, 2003
    Location:
    Somewhere in NJ
    Thanks Todd and krich97,

    I actually meant rich, but wrote lean. I think my brain was running lean... ???

    I suppose I'll keep an eye on both (EGR and fuel) for the time being. Maybe I'll try Getty...around here I've heard that they run 10% EtOH in the winter instead of MTBE. Maybe that will make a difference.

    I'm also interested in Phil's comment about running the S/C without the belt (actually NOT running the S/C). This would take me a ways to telling me if it was indeed the S/C or just some weird fuel thing, etc. But I'm really reluctant to pull the belt for fear of damaging something.

    Tom
     
  15. ppc

    ppc M Go Blue

    Messages:
    1,796
    Likes Received:
    406
    Joined:
    Aug 18, 2003
    Location:
    Nashville, TN
    Tom,

    You didn’t answer the question I had about the location of the sensor for the EGT. What others have said about lean conditions raising temps is true but a rich condition as someone else suggested can cause increased temps in the exhaust from unburnt fuel collecting in the catalytic converter. If the probe is close to the converter higher temps may be registered

    In a normally operating engine the fuel mixture is always oscillating from lean to rich in order for the catalytic converter to properly operate. Checkout this link for details: http://www.autoshop101.com/forms/h64.pdf. Also check out http://www.autoshop101.com/forms/h61.pdf for EGR. You may have something like a coolant temp sensor malfunction which could disable the EGR. There are just so many possibilities and I can’t disagree with what anyone has proposed.

    I know it’s hard to exactly describe what you previously observed with what is now occurring but you really haven’t given enough information in your initial post. Exactly how much under/over the 1200 mark are we talking about on flat grades? 10/25/50/75 degrees?

    You gave good information on conditions when towing in the summer but then you say same speed now under mild loads? Is that just without the trailer going over the same grades? Are you carrying the same number of passengers etc. A little more detail will help. Can you hookup the trailer and take a test drive?

    I find that once at normal operating temps and underway the EGT readings aren’t going to significantly change winter versus summer with the exception of sitting at idle and how fast changes to the readings occur.

    Every different fuel will have a unique burn temp at the ideal 14.7 to 1 stoichiometry which the engine control system strive to achieve. That is true whether it be regular, premium, winter/summer formulation, aviation, nitro methane etc.

    [hr]

    To answer your question, the belt can be removed from the supercharger and the engine operates somewhat normally. I would say there is a definite loss in power at higher speeds due to restriction in the intake as compared to a normally aspirated engine. You’re not going to win any races but you will get to where you’re going. I’ve gone about 300 miles still being able to cruise at 80 MPH on the freeway. It sure makes one very appreciative of having the blower.

    Last week I decided to replace all the hoses in the cooling system, thermostat and all the belts. I got up in the morning and had a big bowl of Wheaties and started the job. I got almost done late in the evening and the last thing I had to do was put the supercharger belt on and the upper radiator hose and add the coolant. In haste I put a socket wrench on the idler to swing it down far enough to get the belt over the supercharger pulley. Well it turns out one should approach this differently by having the belt slip over the idler instead requiring less movement and tension on the idler and fewer Wheaties. The f***ing bolt snapped on the idler and the serpentine pulley next to it got damaged by the socket wrench.

    Well I got up the next morning and called TRD to verify that I could run the motor without harming anything. They said it would run but not very good. I also called Dan the man to do some smart shopping. It turns out that the bolt which has an integrated washer was not something that can be purchased separately. You must get the entire assembly at over $200 list price. Hopefully I can extract the remaining portion of the bolt and find a suitable replacement and then just order the pulley from Dan.

    Dan had also spoken with the folks at TRD to confirm being able to still run. He suggested that I try rigging the bypass valve open in hopes improving performance. The supercharger has a bypass valve (~2” dia) that is normally open until engine vacuum drops. When it closes the free spinning supercharger then uses engine power to develop its boost. This is to reduce any parasitic loss incurred by having the supercharger constantly spinning under pressure when not required. This allows incoming air to enter directly into the engine. When the engine accelerates or when the petal is put to the metal the valve closes causing a restriction when running beltless. The weather was so cold I decided to see what would happen without messing with it. That is where I currently stand. I will try this modification in the next couple of days so that Dan, myself and the rest of the blower equipped owners will know in the future in case of a broken belt or other failure.

    I did notice when I started the engine at high Idle the blower was slowing spinning on its own. As the engine warmed up and idle reduced the spinning slowed as well until at normal idle it stopped completely. I would guess at speed going down the road it would be spinning much faster. I didn’t see any significant change in A/F or EGT values other than without boost the EGT wouldn’t go much over 1300 degrees which is the norm while cruising down the freeway not under boost.
     
  16. Riley

    Riley

    Messages:
    1,615
    Likes Received:
    11
    Joined:
    Jun 20, 2003
    Location:
    Fort Langley, BC
  17. Scamper

    Scamper

    Messages:
    1,460
    Likes Received:
    2
    Joined:
    Mar 28, 2003
    Location:
    Somewhere in NJ
    [quote author=ppc link=board=2;threadid=8783;start=msg76689#msg76689 date=1071633034]
    You didn’t answer the question I had about the location of the sensor for the EGT.
    [/quote]

    Phil, the sensor is about 6 inches below the flange on the exhaust manifold. I had installed it just as George S. had suggested on his site.

    Used to run about 1100-1150F on flats (during the summer), now I run about 1200-1250 on same flats (in winter)--all with essentially empty truck (me and the missus). I mention the season becuase as you know the ambient temperature is part of that temperature. So if the ambient is 50F colder, all things being equal, the EGT should be 50 less.

    Yeah, I made that a bit confusing... I don't have comparable info since I've not pulled the trailer recently. What I'm seeing is 13-1425F on grade with the trailer (2500#) in the summer. Now, I see similar, if not slightly higher temps, going up same grades (that's the mild load I was referring to) but without pulling the trailer.

    I didn't mention it before becuase I didn't remember to do so, but I have noticed that the temps rise VERY quickly now when I get on the accelerator. Used to just mosey on up...now it moves up noticably quicker to the high temps. Nothing quantitative here...just an observation.

    Well...that's good to know. I thought that all the air flow went through the blower and that it was totally positive displacement, but I guess that's not correct.

    My method for this is to use a good-old-fashioned pipe wrench on the spring-loaded idler arm that comes with the S/C. You can place it right on the houseing which is easily accessible, and avoid using that bold.

    This is what I was unsure of...I knew about the bypass, just didn't get that you needed to rig it to stay open. Let us know what you end up doing to make this happen...the necessary parts will become a standard part of my running gear.

    Thanks much,

    Tom
     
  18. ppc

    ppc M Go Blue

    Messages:
    1,796
    Likes Received:
    406
    Joined:
    Aug 18, 2003
    Location:
    Nashville, TN
    Tom,

    The pipe wrench method sounds like the way to deal with the tensioner. I'll never trust putting that kind of pressure on that bolt again. Thanks for the tip.

    Based upon the details you have provided I would rule out anything "normal" such as reformulated fuel. A 100 degree difference in running on the flats is quite significant.

    I think the EGR still may be an area to check as well as O2 sensors but I'm thinking fuel system might be the primary thing to check. Ideally seeing that you have an ODBII system is to get hooked up to something that will monitor the critical parameters while taking a test drive.

    This summer I had some problems with the fuel pump that kind of appeared all of the sudden while I was towing. I didn’t really see so much of a change in EGT but the A/F meter was going crazy and the engine stumbling. During colder weather the engine would stumble during the first mile or so. It turned out to be the fuel pump failing. I have a rising rate regulator installed piggyback to the OEM fuel pressure regulator so any weakening of the pump pressure is going to be amplified. When the fuel pump was operating in is low voltage mode it just couldn’t supply the pressure/volume that was required. I removed the fuel pump relay that is mounted on the inner left fender and wired directly across the connector so the fuel pump always sees full battery voltage. I have to credit Robbie for that tip. This corrected my problem as well as making the truck run better than it ever had, even before the supercharger install. After the supercharger was installed I would accelerate away from a light and the first couple seconds the engine did OK but then would really take off. I found that this is when the ECU switched the fuel pump to high voltage. I was always going to add a vacuum/pressure switch to override the ECU but eliminating the relay is turned out to be a better fix.

    This worked great around town but when on the highway for over an hour the pump crapped out again so I put the relay back in to finish the trip. I’m now working with C-Dan to replace the pump with one from a turbo Supra

    I’d suggest that you override the relay as a test to see what happens.
     
  19. Scamper

    Scamper

    Messages:
    1,460
    Likes Received:
    2
    Joined:
    Mar 28, 2003
    Location:
    Somewhere in NJ
    Phil,

    Thanks for the analysis. Things may be beginning to make some sense. I had posted a couple of weeks ago about something that might be called "stumbling" or missing under load/acceleration. It seemed/felt like it might be fuel related and I did a fuel system cleaning which seemed to help. These two seeming unrelated things may be dovetailing nicely...

    Just consulted the oracle on this matter (FSM)...seems that the fuel pump relay for a 97 is mounted on the firewall next to the diagnostic port. Here's the funny part (at least I find it funny ::) ), what people have been referring to as the odd bit of electrical stuff/block that needs to be removed to get the antenna motor out, is the fuel pump resistor! Who'd a guessed that!? :D

    But I need some advise on the jumping part. I don't have an electical manual...did Robbie tell you which pins to jump? Any certainty that they would be the same on a 97 as on a 93?

    Lastly, why don't you just replace the LC's pump with another LC pump...? Is it just the hassle of getting to it? Dan's dogs are getting hungry with the new lubrication ventilation system he's installed in his block. :D

    :cheers: Tom
     
  20. ppc

    ppc M Go Blue

    Messages:
    1,796
    Likes Received:
    406
    Joined:
    Aug 18, 2003
    Location:
    Nashville, TN
    Tom,

    I have a 94 Electrical Wiring Diagram manual, a little spendy to get but a great investment. It contains the diagrams in addition to a lot of test measurements etc. Also shows where all the components are located, where the harness run, grounding points, connector pinouts and shapes etc.

    I sure someone can check their manual for the 97 but I’ve included a scan of the area from my 94 manual.

    Pin 5 of the connector, red with green stripe comes from the circuit opening relay and is the power source
    Pin 3 of the connector, red with black stripe is the direct connection to the fuel pump
    Pin 2 of the connector, red with white stripe is the connection to the resistor that goes to the fuel pump
    Pin 1 of the connector, white with red stripe goes to the ECM and controls the switching of the relay.

    I simply made a jumper that plugged into pins 3 and 5 of the connector. I think I used a 10 gauge wire (overkill but I wanted it stiff) with some crimp on spade connectors. I used my Dremel to cut down their width, one slightly the other about half the width so they fit snugly into the connector. I bent the wires over the side and taped everything up real good. I didn’t want any stress on the pins themselves. Its easy to un-tape and put the relay back in it so required without the use of tools. :banana:

    I’ve decided that the OEM pump isn’t up to the requirements I have using the adjustable fuel pressure regulator. Normal fuel pressure is 38-44 PSI and at peak boost I want about 70 PSI available. The turbo supra is a higher capacity pump that according to testing that Christo, Robbie and Ben have done fits nicely although being fatter, is quiet and gets the job done for the same price that the OEM Land Cruiser pump sells for. I was going to choose the Walbro 190 lt/min pump at about half the cost but was concerned that noise was an issue. If I was replacing yours I think I would make the same choice. Check with Dan for the details. My dogs have also been hungry and I’ve already sent a couple of bags of food to Dan for my cooling system and knuckles otherwise it would already be installed.
    :cheers: