Car RamRod Posted March 19, 2008 Share Posted March 19, 2008 Well I have a good 1000 miles on my 87 renix 4.0. I have some spare time this week and I'd really like to get a few more mpg out of her; I'm only getting 15 city/highway and I drive pretty easy, shift at 26-2800. I'm definitely gonna put the 02 sensor and see how gummed up it is from the last engine and breaking this one in. Then what else is there to check (I know the renix engines can be picky) that could lead to my truck not running that well. And it is definitely running rich, I passed emissions by a hair due to running too rich. So what would you guys suggest that I check out? And how? Thanks Matt Link to comment Share on other sites More sharing options...
jtdesigns Posted March 19, 2008 Share Posted March 19, 2008 I wonder how much more you could get with a less restrictive intake?? Link to comment Share on other sites More sharing options...
Oizarod115 Posted March 19, 2008 Share Posted March 19, 2008 I wonder how much more you could get with a less restrictive intake?? wouldn't be worth the time, the HO motors seem to get worse mileage anyways :dunno: the 99+ intake might help, but you have to adapt TPS and all sorts of stuff and swap power steering setups Link to comment Share on other sites More sharing options...
Car RamRod Posted March 19, 2008 Author Share Posted March 19, 2008 I wonder how much more you could get with a less restrictive intake?? wouldn't be worth the time, the HO motors seem to get worse mileage anyways :dunno: the 99+ intake might help, but you have to adapt TPS and all sorts of stuff and swap power steering setups yuck....I don't need any more big mods lol. I was really just curious what I need to check/adjust Renix wise to try to get better mpg, and also to lean it out a bit. Link to comment Share on other sites More sharing options...
ifixit8 Posted March 19, 2008 Share Posted March 19, 2008 I just figured out what I got mpg this last fillup. I got 11mpg. then again I remote start the thing alot and I drive about 8 mins to work. not good for any vehicle. I can't wait till it warms up more, then I can drive my tiburon or my motorcycle. Link to comment Share on other sites More sharing options...
BLHTAZ Posted March 19, 2008 Share Posted March 19, 2008 Check out my thread on Fuel Injectors here... http://comancheclub.com/forums/viewtopi ... highlight= They are a very big bang for the buck as I have increased my MPG from 14.5 to 17.25 just from changing them in my '88. It's never guaranteed that you will get the same results as there are too many variables, but you should see some improvements. I have put these in our '95 YJ as well as a friends '97 TJ. The YJ and TJ were very recent so I don't have any MPG reports on them yet, but the idle smoothness, acceleration and throttle response were all noticeably and immediately improved in both so far. Link to comment Share on other sites More sharing options...
Randy in Maine Posted March 19, 2008 Share Posted March 19, 2008 If it were me: 1) I would first do a compression test to see what kind of shape the engine is in. If compression is leaking out someplace, a leak down test will isolate it. 2) Have a look at the tires to see how close they are to the stock size. Too tall will really gear it up too much and will also throw off the speedo. 3) Correct tire pressures are important. 4) If you jack it up, do the brakes drag? 5) Are you leaking gas somewhere or is your gas cap not correct? Is your fuel pressure correct? Spark plugs black? Got any vacuum leaks? Link to comment Share on other sites More sharing options...
Car RamRod Posted March 19, 2008 Author Share Posted March 19, 2008 Check out my thread on Fuel Injectors here... http://comancheclub.com/forums/viewtopi ... highlight= Thanks for the idea. I may not go for those right away, but I have a set of low mile 19#ers out of my car, which should be better than the 270k ones I'm running. I totally overlooked the injectors. If it were me: 1) I would first do a compression test to see what kind of shape the engine is in. If compression is leaking out someplace, a leak down test will isolate it. 2) Have a look at the tires to see how close they are to the stock size. Too tall will really gear it up too much and will also throw off the speedo. 3) Correct tire pressures are important. 4) If you jack it up, do the brakes drag? 5) Are you leaking gas somewhere or is your gas cap not correct? Is your fuel pressure correct? Spark plugs black? Got any vacuum leaks? Thanks for the ideas randy, here's what I have covered already the engine is freshly rebuilt, so compression shouldn't be a problem. I'm running 31's, so they shouldn't kill me too badly. But my speedometer is off anyway from the speedo gear I'm using so that part doesn't affect me. The brakes and all should be alright, but I'll check. And I'll pull a plug soon and check it out for sure. Could be a small vacuum leak here and there, I need to fix up the vacuum fittings with some RTV just to be sure. Also, anyone know how I could check the condition of the o2 sensor? Thanks for the suggestions, Matt Link to comment Share on other sites More sharing options...
Randy in Maine Posted March 19, 2008 Share Posted March 19, 2008 At 1000 miles, your new rings should be broken in by now. I am still learning the Renix FI set up myself, but there should be a way to measure the output of the O2 sensor using a volt ohm meter att eh wiring harness to see if it is sending the correct voltage (I want to say that it should be in the order of 0.5 volts) output to the FI ECU saying "too rich". Sometimes they get "lazy" if they have been run too rich for too long. Sometimes, if you have used a "non-sensor safe" RTV sealant somewhere that will also throw it off. You can also do a check of the injector spray pattern to see if it is atomizing the fuel correctly. When I get home I will attach a link to the Renix FI troubleshooting pages, but I don't have it handy right now. Compare the diameter of the 31" tires to the stiock size you have to see how far it is throwing off the odometer. Example, if you are running a 31x10.50x15 tire it will throw off the odometer by about 14.27% over the stock 205/75/15. Link to comment Share on other sites More sharing options...
BLHTAZ Posted March 19, 2008 Share Posted March 19, 2008 Correct...and with the speedo being off, the odometer is going to be off and therefore throwing off your MPG calculation ;) . If the o2 sensor has not been replaced, you should just do it as that is a regular maintenance item that should be replaced about every 60K anyway. :cheers: Sounds like you are on the right path to making improvemnets though. Link to comment Share on other sites More sharing options...
Pete M Posted March 19, 2008 Share Posted March 19, 2008 I'm running 31's, so they shouldn't kill me too badly. But my speedometer is off anyway from the speedo gear I'm using so that part doesn't affect me. There you go. You aren't getting 15 mpg. All you math is off. :D Get the correct speedo gear in there and retest. Link to comment Share on other sites More sharing options...
Car RamRod Posted March 19, 2008 Author Share Posted March 19, 2008 I'm gonna just go ahead and change the o2. It came out of a 273k truck so it's probably due. As for the speedo being off, it's more than just the tires. I have larger tires than stock, but I also have a 3.08 speedo gear in a truck with 3.55s, so I'm not even going off that (even though I would like to fix it sooner or later). Randy if you could post that link up when you get a chance that would be great. Matt Link to comment Share on other sites More sharing options...
Pete M Posted March 19, 2008 Share Posted March 19, 2008 How are you calculating your mpg? Link to comment Share on other sites More sharing options...
Car RamRod Posted March 19, 2008 Author Share Posted March 19, 2008 How are you calculating your mpg? 15.4 miles to school each way. I do that 3 times a week.....and don't drive it anywhere else lol. Link to comment Share on other sites More sharing options...
Randy in Maine Posted March 19, 2008 Share Posted March 19, 2008 Well I don't have much but this is where I got it..... http://www.greatlakesxj.com/tech/Renix_ ... Manual.pdf Page 41/46 Thanks go to great lakes for putting that up! Here is a handy website for comparing various tire sizes.... http://www.1010tires.com/TireSizeCalculator.asp Link to comment Share on other sites More sharing options...
boman40 Posted March 19, 2008 Share Posted March 19, 2008 Well I was looking through this form when the Grand Cherokee's fuel pump went out. So I decided to put new injectors in with the fuel pump, also had to replace the fuel regulator. Since taz's fuel mileage when up I thought it was worth the money, bought three sets, did the Grand cherokee first, with 186,000 miles on it. Check the mileage after the injectors were installed, went from 13 to 15 in town to 17.5 mpg. I was impressed, so I change the 92 cherokee and the 89 mj injectors too. Now need some over time for the 95 cherokee injectors. This is a great price on the injectors and would recommend this to anyone with 100,000 miles or more on their engines. don't forget to change the fuel filter too. Link to comment Share on other sites More sharing options...
Oizarod115 Posted March 20, 2008 Share Posted March 20, 2008 31" tires are definitely going to affect your gas mileage and it's not gonna be positively. 15 isn't really that bad honestly. hell, i just searched ford and a 2008 3.0L v6 ranger is rated 15mpg city, and 20 hwy... and thats a 2wheel drive with 235/75r16s. Link to comment Share on other sites More sharing options...
BLHTAZ Posted March 20, 2008 Share Posted March 20, 2008 Well I was looking through this form when the Grand Cherokee's fuel pump went out. So I decided to put new injectors in with the fuel pump, also had to replace the fuel regulator. Since taz's fuel mileage when up I thought it was worth the money, bought three sets, did the Grand cherokee first, with 186,000 miles on it. Check the mileage after the injectors were installed, went from 13 to 15 in town to 17.5 mpg. I was impressed, so I change the 92 cherokee and the 89 mj injectors too. Now need some over time for the 95 cherokee injectors. This is a great price on the injectors and would recommend this to anyone with 100,000 miles or more on their engines. don't forget to change the fuel filter too.That's good to hear. I know that I have not heard anyone say they were unhappy with the changes so far. I have done it to two of my three vehicles and should soon change the ones in my 2002 Dodge Ram 4.7L. We are working on a magazine article about these injectors right now for a large Jeep magazine called Jrations. I have sent your statement from above to them, but if you wish for it to not be used, just let me know and I will have them drop it. I don't know if they will use it or not, but I thought I would send it as it would be cool (in my opinion) to have some testimony other than mine and the guy writing the article in there ;) . Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted March 20, 2008 Share Posted March 20, 2008 I bought these injectors also. I can't tell you if it improved my gas mileage because of other problems with vacuum leaks and such. However I did get better acceleration, faster starting times, and improved drivability. Not only that but I also lost 19 pounds on the Precision injector diet and you can too. Just look at me now. :jump: Link to comment Share on other sites More sharing options...
BLHTAZ Posted March 20, 2008 Share Posted March 20, 2008 :chillin: Chico...you're a freakin' riot... :rotfl2: :rotfl2: Link to comment Share on other sites More sharing options...
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