Oyaji

Brett, here's the IAT/MAT temp vs. ohms chart for the early HOs. This is from the 91 FSM. As you can see, the ohm values are quite different throughout the temp range. I don't know how well this sensor would work in a Renix system, and how much weight is assigned for the IAT signal by the Renix computer. Aren't the connectors different too? The Renix and HO IAT's are completely different animals. I think cleaning the tip up with Berryman's carb cleaner and a Q-tip would be best to try first. Ans aftermarket IAT sensors are still available as I'm sure you know. HTH.......... Image Not Found FYI: that chart has Fahrenheit and Celsius headings reversed - make sure to remember that if you ever use it.

Couple of practical suggestions for you: Use of a good penetrating oil will reduce the chance of twisting off a stud; chase it with a heavier oil as you disassemble. Also take care to wire-brush the threaded potion of any fastener you can reach; doing a good job there will help get the nut off more easily. Finally, be patient and move the nut only a little, alternately tightening it after every bit you loosen it. "Rocking" the nut back and forth will work it loose by stages, and minimize the risk of twisting it off. Replace the nuts with (1-use) copper-coated nuts to make disassembly easier next time, too. Also, for any vehicle you plan on keeping for the long term, it pays to have back-up parts in your own inventory for when it's time to work on it. A spare head would allow you to spec it out to your satisfaction during your spare time (porting including match-porting the manifolds if you have spares of them too, "CCing" the combustion chambers, and multi-angle valve jobs come to mind here. :)). A head swap is much less time consuming when you don't have to wait for the machinist, and cuts the amount of time your vehicle is off the road.

Rock-solid advice - and very nice economy figures, too! I am curious - did they flow-match your injectors when you sent them off? How much did they charge you for the service, and what fuel economy gain did the matched injectors return for you?

Yes. Assuming an engine running on all cylinders and in a reasonable state of tune, fine-tuning driving habits unquestionably offers the biggest opportunity for fuel economy gains. You don't need to take my word for it - go Google it for yourself and read any site geared toward improving fuel economy. None of this has any effect except at wide-open throttle (WOT). Tugalo is seeking fuel economy gains, not maximum power with the throttle mashed to the floor. Some of what you mentioned is erroneous and misleading. Benefit from 4 hole injectors would be predominantly from low RPM running to help beat the idling exhaust emissions test. (Air-shrouded injectors offer the same benefit, but despite seeming promising turned out to offer no benefits elsewhere and thus were dropped for their additional cost and complexity.) However, it is true that reducing emissions under part-throttle running can offer a fuel economy benefit. The main thing to keep in mind about bigger throttle bodies,cold air intakes, and other "snake oil" "upgrades" is that any benefit they would offer is only available at WOT; many times such parts offer no benefit whatsoever as proven by dynamometer testing (some products even return worse test results than stock). Any other time, the limiting factor for air flow is the throttle plate - because it is mostly closed for most engine running conditions. Further, the amount of fuel being injected is not dependent on the injector, but rather the control unit (which for part-throttle operation will compensate for sets of different flow rate injectors by simply taking feedback from the oxygen sensor into account and computing the proper duration injector pulse width). Too little or too much and the engine won't run properly. The engine needs to produce only the power required to equal the load, so increasing injector and air flow rates are not at all the issue here. I'm sure you know that, but I'd guess that like many people you got sidetracked by the allure of parts that seem to offer a logical benefit, and you lost sight of the issue at hand: economy. For someone who willing to modify his vehicle from stock, changing camshaft profile indeed offers potential for economy gains. To reap such benefit, changes are required elsewhere in the powertrain too, to change overall gearing. Getting such dialed in at the factory requires a large budget and time, but a motivated and meticulous individual can accomplish the same thing with patience, knowledge, a willingness to get his hands dirty, and deep pockets. I won't presume to know whether Tugalo is interested in going to those lengths, but considering his age I don't think it is likely. I may be interested in pursuing such changes though, and would be very interested in hearing any details about cam choices, tested and proven degrees of advance on stock and aftermarket camshafts to increase low-RPM torque, part-and full-throttle torque and power curves under steady state dyno loads, and the changes to overall gearing required to take full advantage of the modifications. The upper fuel economy results you mention are phenomenal, particularly in view of common experience. Would you share your method of determining those figures? I think this is the best advice you have given, and I completely agree.

If you have access to an exhaust gas analyzer, you could disconnect sensors and manually substitute known good values as you check the effect of each sensor in turn to isolate (a) bad one(s), but I am guessing that is beyond the capability of most owner/mechanics. I think you should start by fixing what you know is broken and could be the source of your problem rather than starting to replace things that seem to be functioning fine (after all, you did report good running and plenty of power, with just an intermittant problem). Despite the comments that deny or minimize the value of understanding the background of how things actually work and instead endeavor to derail the quest for a fix for the problem at hand, it is no less true that understanding the way things work really does help in troubleshooting and finding the solution to a problem. If after replacing your cracked exhaust manifold you still have the problem, you are no worse off for having completed an easy repair you had to do in any case, and can still continue checking other avenues of solving the problem at hand. If it fixes the problem, you are saved what would otherwise have been a fruitless task of exploring what would have been dead-end avenues. Please keep us updated and let us know of the solution you find.

Just remember that you can swap locations for the pins or discs to match them to the key cut depths, and that you don't have to use all of them (or any of them, if you just want to use the lock as a latch). It really is pretty easy, and interesting and fun as a puzzle can be, too. :) Filing and soldering can certainly be done just as Danbyrambler said, but I'd leave that for a more important lock where security is more of an issue than here where you don't need to use all the tumblers... but you can certainly do that to take it up to the next level!

As I mentioned before, you can use 1 or 2 or none or all or any number in between, but for security use as many as you can. For simplicity, use none or 1. I am guessing this is a very simple and cheap lock, but because it is uses the same blank as your ignition key it might have a feature or 2 that make it harder to get apart. I'm betting that is not the case, but if it is, fiddle with it during commercials while you watch TV. Locks are sometimes like puzzles in that they can provide entertainment that can turn into frustration! :D Be persistent and don't be afraid to fiddle with it - in this case you have nothing to lose. Putting it back together may be easier than taking it apart. If you have trouble, give a shout again here - you may need to "pick" it before you can disassemble it. If so I could coach you on it - if you can pick it, you will have the cylinder turned in 15 minutes, or else give up.

You should be able to slide the cylinder back in using only light finger pressure to hold down the pins/discs. You'll need the same screw driver or Allen wrench to secure the cylinder to the lock body that you used to take it apart. That's it. If all should go horribly wrong and all your pins/discs and springs go shooting off across the room upon disassembly, never to be found (despite my warning to be careful and work slowly! :)), then you are no worse off than you were before; nothing prevents you from buying a replacement cylinder. Even in that case, you could reassemble the cylinder completely empty and the lock would still function as a latch - you would just lose all security as the lock would open with any key or screwdriver, and maybe even with a fingernail.

If you just want a functional lock without worrying about the security it provides, you should consider disassembling the lock and doing your own locksmithing. It is not difficult at all on many locks. I've not taken this particular one apart, but if you locate the pin or screw that holds the tumbler assembly together, it will come apart. Be careful as you very slowly slide out the cylinder - it will contain spring-loaded discs or pins which will be easily lost as spring pressure is released as the components come clear of the lock body (they can shoot across the room if you aren't careful to retain and release them gently with a finger). Lay out the pins or discs in the order they come out. Compare the lengths of the pins/slots in the discs. There will most likely be 5 steps in the lengths; they will correspond to the depth of the cuts in the key you want to use. Match at least 1 or 2 of the pins/discs (at least - more add security and make the lock harder to pick) to the corresponding cuts in the key, load them into the proper location in the lock cylinder, and carefully reassemble. Congratulations - you have just re-keyed your lock to the key of your choice. :)

Since the driving cycle I posted is for the EPA Fuel Economy test, it has everything to do with the topic of this thread. As can be readily seen by reading it, the maximum speed of the test is 60 MPH, and the average is 48.3. That is the speed range for which vehicles for the US market were designed to deliver best economy.

What it does show is the highway driving test cycle for which vehicles of that time were optimized. I didn't bother to look up the 1987 Arizona speed limit because it had no bearing on the design of vehicles for the American market.

Detailed Test Information EPA tests vehicles by running them through a series of driving routines, also called cycles or schedules, that specify vehicle speed for each point in time during the laboratory tests. For 2007 and earlier model year vehicles, only the city and highway schedules were used. Beginning with 2008 models, three additional tests will be used to adjust the city and highway estimates to account for higher speeds, air conditioning use, and colder temperatures. Note: EPA has established testing criteria for electric vehicles and plug-in hybrids that are slightly different than those for conventional vehicles. Highway: Represents a mixture of rural and Interstate highway driving with a warmed-up engine, typical of longer trips in free-flowing traffic. http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

Yikes! Never thought to check the post dates, thought it was today. Belated best wishes then - better late than never, one would hope.

You guys do have a point about your experience with engine speed and economy. I guess I should point out that the factory engineers designed the entire powertrain to return best economy to beat the EPA test back when the speed limit was 55 MPH. They certainly did the best job they could and no individual can match the R&D budget of the entire corporation they had behind them, but still, as they were fond of saying (and still do in their disclaimers), "your mileage may vary"! :D Doubtless driving a vehicle under the conditions it was designed for will yield the best results. As for some of the other stuff, well... maybe more on that later.

:( Please accept my best wihes for a speedy recovery, Pete. Hope you feel better soon.

Back in the day, word was that if there was no antenna load and the mic was keyed the power would "backfeed" into the circuitry and burn something up. Are CB radios of today overload protected against this, or is it still a potential problem?

Welcome, Josh. When you are working on the lowering part, make sure to take pics and post them, please. I for one will be curious about your progress and results, particularly if you should decide to go with any sort of variable height suspension. :)

No, it is true for all 4-stoke engines no matter how many cylinders. By the time the flow reaches the tailpipe, friction all along the length of the exhaust pipe as well as the baffles and chambers in the muffler will have smoothed out the flow and thus canceled the pulses. (After all, the compression and rarefaction pulses are what defines sound, and one of the main purposes of the exhaust system is to muffle sound.) But the closer you get to the exhaust valve, the more pronounced the pulses are. One of the things I'll do when I get around to fabricating my exhaust is to use an old air-injection reed valve with a venturi in the exhaust to create negative pressure for my substitute PCV, to replace the standard stock setup to the intake manifold. It'll make the exhaust smoke a bit (maybe backfire too?) and will not by any means be road-legal by emissions standards, but it will keep my intake manifold and valves from getting all gunked up with blow-by and oil.

Good advice as always. But the exhaust system (particularly at the manifold) is not always under positive pressure. It does fluctuate with every opening and closing of exhaust valves, and the rarefaction pulse that follows every compression pulse will indeed create waves of negative (lower than atmospheric) pressure. Remember the reed valves that fed fresh air into the exhaust on old air-injected emissions reduction systems? The above was exactly the principle that made them work. Similarly in tuned exhaust headers, that pressure wave is amplified through the use of harmonics (like a pipe organ) to scavenge exhaust via negative pressure pulses, too.

Though I can turn a wrench and burn a rod well enough to get though most repairs, I certainly lack the experience that you and others here have to offer. Specific Jeep knowledge is invaluable when working on Jeeps, and my knowledge, as I have mentioned before in other posts, is of a more general kind and not nearly as helpful when there is a specific task at hand. I hope to benefit from your knowledge, as I am sure many others here will, so please don't be too shy in the future to chime in constructively. Between us, there should be no problem too big to whip. :)

Welcome back. This should be fun. :)

:jump:

:waving: The first step in fixing a problem is recognizing that there is one. Defining the problem is half the work of designing a solution for it. Now, how about them mirrors? In the effort to reduce drag, one cutting-edge solution has been to rely on exterior cameras with displays in the cabin. Many may think them impractical, but I thought I'd just throw the idea out there anyway...

The cracked exhaust manifold might be allowing pulses of air (and thus oxygen) back into the exhaust system, thus throwing off the oxygen sensor reading.

Aluminum transfers heat better than cast iron, but the limit on how much heat can be transferred is from coolant flow and the heat sink (radiator). Advantage would be in hot-spot reduction (mainly from fast heat build-up resulting from high-load demand suddenly applied) and, of course as you mentioned, weight savings.