BlkndGoldCutlass Posted November 3, 2012 Report Share Posted November 3, 2012 (edited) I know this question has probably been posted here before but bear with me please. i would rather have answers closer to my circumstance. Thank you Well i own a 1993 cutlass supreme with the DOHC 3.4l, i am getting very poor gas mileage (like 8mpg). i have myself replaced the EGR, IAC valve, PCV valve, Plugs, Wires, Battery, Oil change, and new tires. All with just a little increase. i have fixed the vacuum leak i once had, still no fix. The car is 100% straight piped so no back pressure so that might hurt me a little? ive read that it may be the 02 sensor or MAF sensor etc... She does have a weird idle surge and no codes r being thrown I am a knowledgeable high schooler with access to a shop so please don't noob me, i appreciate all answers thank you! Edited November 3, 2012 by BlkndGoldCutlass Quote Link to comment Share on other sites More sharing options...
Crazy K Posted November 3, 2012 Report Share Posted November 3, 2012 since it is a 93... have you verified that the rear brakes aren't locked up? I've seen that kill mileage. Also, the 3.4 tends to need intake gaskets to solve a leak there, so you might have to check that out... but usually it is associated with hard starting. Quote Link to comment Share on other sites More sharing options...
19Cutlass94 Posted November 3, 2012 Report Share Posted November 3, 2012 Fix the idle issues and go from there. The weird idle could be a bad sensor,gaskets or a vacuum leak. All of which will cause issues. How big is the exhaust? If it is stock size, just straight piped, it still has plently of backpressure, which wont affect it. Just make it sound.... different. Quote Link to comment Share on other sites More sharing options...
rich_e777 Posted November 3, 2012 Report Share Posted November 3, 2012 What kind of smells are detected? heavy exhaust or fuel odors? Fluid leaks? Spark plugs gapped correctly? Exhaust leak? i know on a 3100 if there isnt splash shields on the inside of the vavle covers oil can get sucked up through the PCV sytem into the UIM or plenum. Oil in the PCV valve would indicate that. What kind of fuel do you use and have you had your injectors cleaned? Battery terminals clean? Bad Coil pack? Tranny fluid and filter change? Just naming off some stuff that comes to mind. Any other modifications on your CS? Probably gonna need to see some pics, im a Cutlass fan of all years. Quote Link to comment Share on other sites More sharing options...
Galaxie500XL Posted November 4, 2012 Report Share Posted November 4, 2012 '93 should be MAP, not MAF... Your best bet would be to get ahold of a scantool, and see what's going on. O2 sensor will DEFINITELY kill gas mileage, but I've never seen one so far gone to cause 8 MPG without it also setting codes. Besides, it's not much fun to replace an 02 sensor on a DOHC...I did mine while the plenum was removed while doing a timing belt replacement, which wa about the only way I could figure to actually get access to the sensor. Quote Link to comment Share on other sites More sharing options...
BlkndGoldCutlass Posted November 4, 2012 Author Report Share Posted November 4, 2012 yes plugs are gapped correctly, stock exhaust size, running 87 octance, no exhaust leak, new battery no corrosion, i do need a tranny flush i know. I do have a snap-on Solous scanner and its not showing anything. She has had a hard time starting lately and now that u mention it there was oil in the pcv valve. So does that mean i have a bad intake manifold gasket? Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted November 4, 2012 Report Share Posted November 4, 2012 I did mine while the plenum was removed while doing a timing belt replacement, which wa about the only way I could figure to actually get access to the sensor. perfect excuse to do all three. Quote Link to comment Share on other sites More sharing options...
rich_e777 Posted November 5, 2012 Report Share Posted November 5, 2012 (edited) yes plugs are gapped correctly, stock exhaust size, running 87 octance, no exhaust leak, new battery no corrosion, i do need a tranny flush i know. I do have a snap-on Solous scanner and its not showing anything. She has had a hard time starting lately and now that u mention it there was oil in the pcv valve. So does that mean i have a bad intake manifold gasket? pcv should be connected to the valve covers not intake manifold, and underneath those covers are the rocker arms,springs and oil. and the pcv valve is sucking air from there right back into the Upper intake manifold/plenum after the throttle body. Sounds stupid to me but im not a GM engineer, so i dont thin that would indicate a leak. But thats on a 3100 but should be same/similar ona LQ1. Do you have all the spark plug wires plugged into the correct coil pack terminals? Shit does happen. When did this first start? and what was changed when it did? Edited November 5, 2012 by rich_e777 Quote Link to comment Share on other sites More sharing options...
BlkndGoldCutlass Posted November 6, 2012 Author Report Share Posted November 6, 2012 Yeah all plugs and wires are fine pretty sure the packs are too. i just checked out ALLDATA and they are telling my the oil in the pcv valve is a sign that the "positive crankcase cover" needs a new gasket/seal? Does this seem like a viable cause? Quote Link to comment Share on other sites More sharing options...
rich_e777 Posted November 8, 2012 Report Share Posted November 8, 2012 (edited) never heard of a positive crankcase cover, if anything tht might be the splash shield inside the valve cover, just underneath the pcv valve itself, on the 3100 anyways. Where on the LQ1 is the pcv system routed through? Edited November 8, 2012 by rich_e777 Quote Link to comment Share on other sites More sharing options...
BlkndGoldCutlass Posted November 10, 2012 Author Report Share Posted November 10, 2012 The PCV valve on the 3.4 seems to come out right next to the intake manifold/throttle body and egr valve all the way the the center of the engine under the plastic cover, ill take a pic of it in the am for ya Quote Link to comment Share on other sites More sharing options...
chadz34 Posted November 10, 2012 Report Share Posted November 10, 2012 I know this question has probably been posted here before but bear with me please. i would rather have answers closer to my circumstance. Thank you Well i own a 1993 cutlass supreme with the DOHC 3.4l, i am getting very poor gas mileage (like 8mpg). i have myself replaced the EGR, IAC valve, PCV valve, Plugs, Wires, Battery, Oil change, and new tires. All with just a little increase. i have fixed the vacuum leak i once had, still no fix. The car is 100% straight piped so no back pressure so that might hurt me a little? ive read that it may be the 02 sensor or MAF sensor etc... She does have a weird idle surge and no codes r being thrown I am a knowledgeable high schooler with access to a shop so please don't noob me, i appreciate all answers thank you! Try some 91 octane fuel. Quote Link to comment Share on other sites More sharing options...
BlkndGoldCutlass Posted November 10, 2012 Author Report Share Posted November 10, 2012 Well i used to run 91 but the cost was just too much for me lol, i have been running fuel injector cleaner to raise the octane too see if that helps but it doesnt really do to much. Quote Link to comment Share on other sites More sharing options...
chadz34 Posted November 10, 2012 Report Share Posted November 10, 2012 I noticed this in my Z34, and especially with the Ben Chip. Other members might not believe in high octane fuel for the LQ1, but I have two and they like it. My Z34 has always felt a little rougher with regular 87 octane and its literally MINT. Give it a try. Quote Link to comment Share on other sites More sharing options...
GP1138 Posted November 10, 2012 Report Share Posted November 10, 2012 Well i used to run 91 but the cost was just too much for me lol, i have been running fuel injector cleaner to raise the octane too see if that helps but it doesnt really do to much. It's not that much more expensive. Quote Link to comment Share on other sites More sharing options...
BlkndGoldCutlass Posted November 10, 2012 Author Report Share Posted November 10, 2012 Yeah ill give it another shot i suppose, Im still concerned with the throttle surge. When i decelerate to a stop or slow at a light the rpms will surge from like 300-1000 sometimes killing it. It confuses the hell out of me lol, Maybe a TPS sensor? Quote Link to comment Share on other sites More sharing options...
z34dumas Posted November 10, 2012 Report Share Posted November 10, 2012 or idle air sensor... Quote Link to comment Share on other sites More sharing options...
BlkndGoldCutlass Posted November 10, 2012 Author Report Share Posted November 10, 2012 Nah i already replaced that along with the egr, plugs, and wires Quote Link to comment Share on other sites More sharing options...
19Cutlass94 Posted November 10, 2012 Report Share Posted November 10, 2012 You do know that injector cleaner is only suppose to be used every 3000-5000 miles right? If used too often that stuff will burn up injectors. Having heard that, I wouldn't be surprised if you have a few injectors that have gone south. Fuel injector cleaner does not boost octane. Even octane booster at best will only raise it 1-2 point which you'll notice more by just switching to 91-93 octane. Sent from my iPhone in some random spot of Texas. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted November 10, 2012 Report Share Posted November 10, 2012 W-bodies have slightly over 16 gallon tanks, but let's say you run from full to nearly empty and use 15 gallons. 15 gallons X 3.49 for 87 = 52.35 15 gallons X 3.69 for 91/93 = 55.35 exactly a $3 difference at the moment locally. how much does a bottle of injector cleaner cost? how much does a bottle of octane booster cost? Quote Link to comment Share on other sites More sharing options...
rich_e777 Posted November 11, 2012 Report Share Posted November 11, 2012 Other than adding fuel injector cleaner as needed all those other additives will just F your engine up alot sooner. Higher octane fuel burns slower thus leaving more deposits and heat. 87 is perfectly fine. I`ve seen cars fail emission because they were running 91 octane, a switch over to 87 and burn a few gallons and they pass. How long has it been like that and what changed right before, has it just been all the sudden or over time? Before or after your exhaust mod? after replacing something else? You might have some internal problems. Drive it pretty hard? heh rhetorical question. Quote Link to comment Share on other sites More sharing options...
BlkndGoldCutlass Posted November 11, 2012 Author Report Share Posted November 11, 2012 I only run injector cleaner only every 2500-3000 miles, i do run 87 octane right now. She acted like this until i replaced the iac valve then it was ok until lately. Quote Link to comment Share on other sites More sharing options...
95LQ1VERT Posted November 11, 2012 Report Share Posted November 11, 2012 Did the IAC Valve come with a new o-ring gasket? When they get older they can crack or stretch out and wont seat properly. At least when I did mine thats what happened. Or you could have a Faulty replacement unit itself, try warrantying it out and get a new one and see if that works better. Quote Link to comment Share on other sites More sharing options...
BlkndGoldCutlass Posted November 11, 2012 Author Report Share Posted November 11, 2012 Yeah it came with a new one and i oiled it too, ya ill try warrantying it lol Quote Link to comment Share on other sites More sharing options...
Crazy K Posted November 11, 2012 Report Share Posted November 11, 2012 can you verify that the TPS sensor is truely at ZERO when the throttle is no applied? Quote Link to comment Share on other sites More sharing options...
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