alec_b Posted October 5, 2010 Report Share Posted October 5, 2010 Yes yes I know - another fuel economy thread. I may be way off base here but it seems to me like my regal should be doing better than it does. I know most of the guys here are 60* guys but I think enough of the club have driven 3800 vehicles to have a good opinion. Car details: '91 Buick Regal GS, 3800 SI 4T60 trans, 3.06 gears. In the last 5k I've replaced (for maintenance not necessarily to solve this issue): fuel filter, plugs, wires, and air filter. Seafoamed once right when I bought it. She's sitting at about 135k right now. So far since I've had the car (about 12k miles) the BEST I've gotten out of it was 25 MPG. That was a 90% highway trip, varying between 60-70 mph. That seems low to me... I know for a fact that most 3800 cars do much closer if not over 30 miles to the gallon on the highway. I've never had an SES light come on now have I ever had any performance problems with the car. I took it out with our work scanner on my break the other day just to see if there was something I was missing, but it all looked fine. Steady cruise at 60 shows my integrator and block learn both around 125-135, which to me seems perfect. O2 values look good and switch correctly. Spark advance was I think 25* or so at a cruise. There's no cat in the car if that makes any difference. I haven't done a compression test, because I didn't think there was a reason to. I do know the lower intake gaskets are leaking a bit, but I hardly think that matters as far as MPG's. Am I just hoping for too much? If 25 is the best I can get I'm OK with it, it's just bothering me because I feel that I can get more. Quote Link to comment Share on other sites More sharing options...
Night Fury Posted October 5, 2010 Report Share Posted October 5, 2010 Yes you should be getting more, check fuel pressure? Quote Link to comment Share on other sites More sharing options...
chrisflstf Posted October 5, 2010 Report Share Posted October 5, 2010 Try cleaning your Mass Air flow sensor - I just picked up about 1.5mpg after cleaning mine. Tire pressure ok? Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted October 5, 2010 Report Share Posted October 5, 2010 125 to 135 is a decent range, it means without O2 correction, you're running from ~14.35:1 - ~15.5:1. don't suppose you were watching knock counts or knock retard during this? and i'm looking at a 1990 regal tune now, and the only place in the spark map where i'm seeing 25* is from 1600-2400 RPM at approximately 144 LV8... that seems kinda high for cruise, since LV8 is determined by engine speed and airflow, with less of either making lower LV8 numbers. and i'm also looking at the TCC locked SA table, and it goes no lower than 33*....... you're certain the TCC is locking? Quote Link to comment Share on other sites More sharing options...
alec_b Posted October 5, 2010 Author Report Share Posted October 5, 2010 Sorry guys it was late and i'd had a few beers last night ha. The TCC is locking properly, both in 3rd and 4th gear. The 25* of timing was a guess it could be wrong. I'm not getting any KR at all under a steady cruise, the only time I saw any was under a hard throttle 3rd gear pull and that was 1* for a split second. I haven't checked fuel pressure yet, I can do that tonight quick at work. I'll also try cleaning the MAF as. I was thinking about doing that anyways. If there's any other data that's necessary just let me know. Oh and it gets up to operating temperature just fine. Sits right at about 187-195 cruising with 60ish degree outside temps. Quote Link to comment Share on other sites More sharing options...
AL Posted October 6, 2010 Report Share Posted October 6, 2010 Do you have a scan tool to read actual timing advance while cruising? Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted October 6, 2010 Report Share Posted October 6, 2010 throttle angle to maintain 55MPH on a flat road? ANY history or current codes stored? hell, IATs while you're at it. Quote Link to comment Share on other sites More sharing options...
BS009 Posted October 6, 2010 Report Share Posted October 6, 2010 This is just my opinion, but I think that these l27's like to have a cat behind them. I've noticed that they have more bottom end torque and I think it probably helps with gas mileage too. I'm also curious which spark plugs you're using. Quote Link to comment Share on other sites More sharing options...
oscar_wilde Posted October 6, 2010 Report Share Posted October 6, 2010 This is just my opinion, but I think that these l27's like to have a cat behind them. I've noticed that they have more bottom end torque and I think it probably helps with gas mileage too. I'm also curious which spark plugs you're using. Possibly just not enough back pressure? Quote Link to comment Share on other sites More sharing options...
BS009 Posted October 6, 2010 Report Share Posted October 6, 2010 Possibly just not enough back pressure? exactly! i'm guessing it's at least a part of the problem. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted October 6, 2010 Report Share Posted October 6, 2010 (edited) http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm http://forums.focaljet.com/team-tech/417204-back-pressure-myth-fact-theory.html http://www.hondacivicforum.com/forum/showthread.php?t=3064 Edited October 6, 2010 by RobertISaar Quote Link to comment Share on other sites More sharing options...
alec_b Posted October 7, 2010 Author Report Share Posted October 7, 2010 Sorry guys no extra data today, got caught up on another project (see thread in interior). I took the MAF out to clean it last night at work, and found out the thing is broken! Well, not the sensor itself, but half of the plastic frame that encircles the hot wires. It was broken almost perfectly in the middle, and the "half moon" chunk that was left was stuck in the TB at an off angle. I fished out the broken piece and reinstalled the MAF after cleaning it. It may just be in my head, but it SEEMS to drive just a little better now. Power delivery is smoother, and after about 75 miles it seems that the MPG's have gotten just a little better. And I doubt the backpressure makes that much of a difference. I've taken the cat out of almost every car I've had and never seen even a tiny amount of economy loss. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted October 7, 2010 Report Share Posted October 7, 2010 you shouldn't notice an economy loss.... on the contrary, it should help economy due to the motor having to not push against it to get exhaust gasses out. Quote Link to comment Share on other sites More sharing options...
BS009 Posted October 7, 2010 Report Share Posted October 7, 2010 I'm sure that taking out a cat would help with most engines out there, however I have heard countless stories about how someone took out their cat as a performance mod to their L27 only to find that they lost most of their low end torque. Quote Link to comment Share on other sites More sharing options...
tornado_735 Posted October 7, 2010 Report Share Posted October 7, 2010 According to my DIC (lolz), I'm averaging 25.5-26 mpg (90% highway) in my L27 powered Olds Ninety-Eight. Granted, this is with shit plugs and wires, a Cam Sensor code 41, and a grounded ICM code 42. If all was kosher, I would probably be averaging about 30. I guess what I'm getting at is that yes, you probably should be getting better mileage. Quote Link to comment Share on other sites More sharing options...
19Cutlass94 Posted October 11, 2010 Report Share Posted October 11, 2010 25 doesnt seem that bad, Im getting 27 with mine. Quote Link to comment Share on other sites More sharing options...
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