unknown_eyes Posted August 13, 2009 Report Share Posted August 13, 2009 I recently installed a new intake plenum on my car after a loping issue. Or rather I had a good friend who is a mechanic by trade install it for me. He commented that there was a lot of carbon build up under the intake manifold and in the throttle that he cleaned and suggested I run a bottle of "sea foam" thru the gas tank. I was afraid to use the sea foam after reading a couple of posts here, so I used a bottle of Techron instead. Also treated her to a couple of doses of WOT. Before the plenum was installed I was averaging 23mpg mixed driving. Now its averaging 20mpg mixed driving. This is the reading the average mpg readout gives, and I also checked it by dividing the miles driven by the fuel used with the same results. It runs smoothly and is not throwing any codes. So I dont think anything is wrong, it just seems odd to have the mpg drop like that. I use Chevron fuel most of the time and thats what I've run thru it to get my average mpg. My driving habits are consistant, as I tend to drive with a light foot, most of the time. Any thoughts? 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 13, 2009 Report Share Posted August 13, 2009 I trust you used the Techron as per the instructions on the proper amount of fuel in the tank? Do you clear ALL perameters in the computer when you run this test?, that might be a moot point as you said that you checked it the old fashioned method When did you get 23 mpg?, cooler weather? You are no longer setting codes? ANY CODES? Are your tires filled to spec or even slightly more than spec? Are you running the same size tires? Same octane?, or lesser, some feel they can use 87 and get away with it, when the car calls for 91, using 87, your MPG will suffer. Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 13, 2009 Report Share Posted August 13, 2009 Rethinking my last statement, your engine calls for regular is that correct? Do they specify octane? Chevron is good fuel, but I would try another fuel on my next trip like Sunoco, etc, to see if you get any difference Have you disconnected your battery since the work was done?, you may need a relearn? A 3 mpg drop is substantial. What do you get if you reset your MPG on the highway for an extended trip, I will get between 25 and 27 depending upon the terrain for HIGHWAY DRIVING Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Ranger Posted August 13, 2009 Report Share Posted August 13, 2009 He commented that there was a lot of carbon build up under the intake manifold and in the throttle that he cleaned That is normal. I clean my TB once a year. I think GM calls for it once every 30K. The stuff inside the intake is normal too. It is a combination of exhaust and crankcase gases from the PCV & EGR. Link to comment Share on other sites More sharing options...
unknown_eyes Posted August 14, 2009 Author Report Share Posted August 14, 2009 I trust you used the Techron as per the instructions on the proper amount of fuel in the tank? Do you clear ALL perameters in the computer when you run this test?, that might be a moot point as you said that you checked it the old fashioned method When did you get 23 mpg?, cooler weather? You are no longer setting codes? ANY CODES? Are your tires filled to spec or even slightly more than spec? Are you running the same size tires? Same octane?, or lesser, some feel they can use 87 and get away with it, when the car calls for 91, using 87, your MPG will suffer. Yes, I did follow the directions on the Techron bottle as per the amount of fuel in the tank. I did clear the codes before I ran my test tank. There were 2 codes present, neither of which I felt would have any impact on mpg. B0429 current for the rear temp control U1016 history for lost communication with powertrain control module, which I figured was from when my mechanic disconnected the battery to perform the plenum replacement. The car has been getting 23 mpg average since I purchased it a few months ago. Although the first time I checked the mpg average the old fashion way was after the decline in mpg. The only code that has come up since the test is the B0429 current, which comes up frequently. I run the tires at 32 psi cold. All the tires are the same size and relatively new. I'm not sure what octane my caddy calls for, I usually run 87, and put 93 in it maybe every 2nd or 3rd tank for good messures. But there is little difference in mpg with the 87 or 93. I was using 93 for the test. And as for an extended trip, I havent driven it any real distance since I purchased it. I drive it 56 highway miles to work on Monday and 56 highway miles home on Friday. The car sits all week. And I usually put 100-150 mixed miles on it over the weekend. The mpg drop puzzles me. I had never checked the mpg average the old fashion way until after the readout changed. I remember reading in another post that the computer determines mpg by the amount of fuel passing thru the injectors. I wonder if the techron cleaned the injectors enough to allow more fuel to pass, thus increasing fuel consumption and lessoning mpg! Just a thought! 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 15, 2009 Report Share Posted August 15, 2009 I want you to do a test for me. I was thinking about you today, your drop in MPG. Lets test to see if your Torque Convertor Clutch (TCC) is locking up. Drive your car at about 55 mph, watch your TACH, at 55 you should be running about 1800 rpm plus or minus, keep your foot on the gas, and gently press your brake, your RPMs should jump up about 200 to 300 rpms. If not, its possible your TCC is not engaging, that would cause about a 10% drop in gas mileage, I think we have determined. Let us know what your find. PS, if your TCC is not engaging you should set a code, if it's slipping it would set a code, but I would like to see the result of this test Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
unknown_eyes Posted August 16, 2009 Author Report Share Posted August 16, 2009 I want you to do a test for me. I was thinking about you today, your drop in MPG. Lets test to see if your Torque Convertor Clutch (TCC) is locking up. Drive your car at about 55 mph, watch your TACH, at 55 you should be running about 1800 rpm plus or minus, keep your foot on the gas, and gently press your brake, your RPMs should jump up about 200 to 300 rpms. If not, its possible your TCC is not engaging, that would cause about a 10% drop in gas mileage, I think we have determined. Let us know what your find. PS, if your TCC is not engaging you should set a code, if it's slipping it would set a code, but I would like to see the result of this test BodybyFisher, I checked the owners manual and it states 87 octane, or higher for optimal performance. I topped it off saturday using Exxon 87 octane. I then checked and reset the codes. I took a drive today and performed the test you described. At 55mph it runs around 1575-1600 rpm. When I depressed the brake pedal the rpm's stay the same. I performed this several times with the same result. I also, checked the codes when I got home and nothing new is present. Will check the mpg the old fashion way next week and see if there is any change. 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 16, 2009 Report Share Posted August 16, 2009 I want you to do a test for me. I was thinking about you today, your drop in MPG. Lets test to see if your Torque Convertor Clutch (TCC) is locking up. Drive your car at about 55 mph, watch your TACH, at 55 you should be running about 1800 rpm plus or minus, keep your foot on the gas, and gently press your brake, your RPMs should jump up about 200 to 300 rpms. If not, its possible your TCC is not engaging, that would cause about a 10% drop in gas mileage, I think we have determined. Let us know what your find. PS, if your TCC is not engaging you should set a code, if it's slipping it would set a code, but I would like to see the result of this test BodybyFisher, I checked the owners manual and it states 87 octane, or higher for optimal performance. I topped it off saturday using Exxon 87 octane. I then checked and reset the codes. I took a drive today and performed the test you described. At 55mph it runs around 1575-1600 rpm. When I depressed the brake pedal the rpm's stay the same. I performed this several times with the same result. I also, checked the codes when I got home and nothing new is present. Will check the mpg the old fashion way next week and see if there is any change. You seem to have a problem with your TCC disengaging, that would cause a loss of gas efficiency, you should have a code, check to see if you do... Its possible you have a mal-aligned brake pedal switch. As soon as you take your foot off the gas at those speeds or depress the brake pedal, the TCC disengages, if its not disengaging your engine will labor and you will consume more fuel Check codes carefully Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
unknown_eyes Posted August 18, 2009 Author Report Share Posted August 18, 2009 Still no new codes. I'll check the brake pedal switch this weekend. Are there any other symptoms to the TCC not disengaging? The reason I ask is, the transmission shifts rough out of park when its been sitting for a while. But otherwise shifts smooth. Just curious if it was related. Also, the code IRC U1016 history, lost communication with powertrain control module, seems to be coming up every time I check codes. 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
growe3 Posted August 18, 2009 Report Share Posted August 18, 2009 Another thing to observe, clear the Average MPG, and then allow at least three tanks of gas to determine what your current Average MPG is. -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
Ranger Posted August 18, 2009 Report Share Posted August 18, 2009 Are there any other symptoms to the TCC not disengaging? The reason I ask is, the transmission shifts rough out of park when its been sitting for a while. But otherwise shifts smooth. Just curious if it was related. Not related. The only symptom to the TCC not engaging is 2-300 higher RPM and a MPG or so loss in mileage. Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 18, 2009 Report Share Posted August 18, 2009 Ranger, I was thinking that if the TCC stayed engaged that it would force a stall, what do you think? I wonder if its staying engaged from a stop?, wouldnt that cause a sluggish acceleration? Mike Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
Ranger Posted August 19, 2009 Report Share Posted August 19, 2009 Absolutely. If the TCC is stuck on (engaged) it will stall the engine. Just like trying to stop a standard transmission without stepping on the clutch. I can't see how it could be engaged from a stop. Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 19, 2009 Report Share Posted August 19, 2009 Thanks for confirming my thinking. So that would mean, that its engaging, but not disengaging, I wonder what is forcing it to disengage? I need to read up, he should be getting a rise in RPM when he presses the brake Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
unknown_eyes Posted August 19, 2009 Author Report Share Posted August 19, 2009 It accelerates smoothly and has not stalled out on me. In fact it seems to run better now that it did when I purchased it. I will reset the average mpg and run a couple of tanks thru it to see if there is any change. But at the rate I drive, it may take a while! I really appreciate you guys giving this some thought! 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
Texas Jim Posted August 19, 2009 Report Share Posted August 19, 2009 It accelerates smoothly and has not stalled out on me. In fact it seems to run better now that it did when I purchased it. I will reset the average mpg and run a couple of tanks thru it to see if there is any change. But at the rate I drive, it may take a while! I really appreciate you guys giving this some thought! That is a good excuse for a weekend "ROAD TRIP." Link to comment Share on other sites More sharing options...
unknown_eyes Posted August 20, 2009 Author Report Share Posted August 20, 2009 It accelerates smoothly and has not stalled out on me. In fact it seems to run better now that it did when I purchased it. I will reset the average mpg and run a couple of tanks thru it to see if there is any change. But at the rate I drive, it may take a while! I really appreciate you guys giving this some thought! That is a good excuse for a weekend "ROAD TRIP." Texas Jim, I've only been on the board a short time. But I get the feeling you look for any excuse to take a road trip! 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
unknown_eyes Posted August 22, 2009 Author Report Share Posted August 22, 2009 I did the brake/gas pedal test again on my way home today at interestate speed. I performed the test 6 times and twice the rpm's increased by 200 rpm's. So I guess I do have the TCC problem. Still no new codes though. I read in another thread that it was ok to drive this way, so I guess I'll just continue to drive it as is. Does anyone know what parts are required to fix, or the cost to have it done at a trans shop. Just wondering about what it will set me back if and or when I can get it fixed. Thanks again guys for the help on this issue. 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 22, 2009 Report Share Posted August 22, 2009 IF your TCC stayed engaged, you would stall coming to a stop Its possible your brake switch is maladjusted or intermittant, if you can force a TCC disengage...I doubt this is a TCC problem, just a control problem Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
unknown_eyes Posted August 22, 2009 Author Report Share Posted August 22, 2009 IF your TCC stayed engaged, you would stall coming to a stop Its possible your brake switch is maladjusted or intermittant, if you can force a TCC disengage...I doubt this is a TCC problem, just a control problem When you say brake switch, are you talking about the "brake light switch" located at the top of the pedal bracket? I just want to make sure I'm checking the right thing. 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
Texas Jim Posted August 22, 2009 Report Share Posted August 22, 2009 It accelerates smoothly and has not stalled out on me. In fact it seems to run better now that it did when I purchased it. I will reset the average mpg and run a couple of tanks thru it to see if there is any change. But at the rate I drive, it may take a while! I really appreciate you guys giving this some thought! That is a good excuse for a weekend "ROAD TRIP." Texas Jim, I've only been on the board a short time. But I get the feeling you look for any excuse to take a road trip! You know...upon further reflection...you may be right. I love hitting the road in the Cadillac and just GOING somewhere...it doesn't make much difference where ...just go... Link to comment Share on other sites More sharing options...
BodybyFisher Posted August 22, 2009 Report Share Posted August 22, 2009 IF your TCC stayed engaged, you would stall coming to a stop Its possible your brake switch is maladjusted or intermittant, if you can force a TCC disengage...I doubt this is a TCC problem, just a control problem When you say brake switch, are you talking about the "brake light switch" located at the top of the pedal bracket? I just want to make sure I'm checking the right thing. I believe the brake switch serves two functions, but I am not 100 percent sure about that. What I do know is that tapping the brake disengages the TCC, now whether the PCM detects the brake switch and passes that along, I am not sure. I dont have my manual handy right now to look into this. Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
JimD Posted August 22, 2009 Report Share Posted August 22, 2009 An '01 Deville will have two switches operated by the brake pedal arm. There are several functions that use "brakes applied" information; TCC unlock, cruise module, traction control module, shift from Park lock mechanism, and of course the stop lights. Perhaps one of the switches is corroded or the chassis connector is loose. Easy enough to remove the switches; rotate the switch body 1/4 turn CCW and it's in your hand. Install is simply push the switch back into the mount and a ratchet mechanism locks it in place. The switch body will come apart so you can inspect the internal contacts. Been there, done that. Switch position adjustment is not difficult. I like to set mine so the very slightest movement of the brake pedal will kill the cruise and flash the stop lamps without actually applying the brakes. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
unknown_eyes Posted August 24, 2009 Author Report Share Posted August 24, 2009 I think the problem may be solved. I did a combination of things recommended. I removed the white light switches and checked them, they did not have any corrosion or visual damage, so I reinstalled them. I also reset the average mpg dash counter. And this next one will tickle Texas Jim, I went on a short road trip!! Only about 120 of mixed driving, but a road trip none-the-less! I refilled the tank with 87 octane Chevron and the mpg gage read 23.8mpg average and the ole fashion way gave me 24mpg. So it's back up to were it was before. I figure one of the light switches was not getting a good connection. Thanks for the suggestions! 2001 Deville, Sterling Silver exterior with Dark Gray leather, 93k miles Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.