Engine idle.

Topic: Engine idle. (Read 1626 times) previous topic - next topic

Reply #15 – February 22, 2007, 07:41:37 AM

Quote from: jcassity;129478

disconnecting the battery cable does nothing and i dont know why people cant seem to get this. People have no problem being perfectly happy with spreading missinformation,, but feel like its too much work to spread the proper information.

Actually, it does do something, and I've proven it to myself over and over. Originally, I thought the NVRAM in the EEC did not require power to retain the memorized codes. Nope! I forced an EGR code, an O2 Sensor code, as well as a TPS code on my '92 F-150 while doing some troubleshooting. After finding an intake leak on the plenum, I disconnected the battery for repairs, but realized I didn't clear the codes before I started the mechanical work. Battery was disconnected for a couple days while the mechanical work was going. First thing I did after reconnecting the battery was run codes to find out if everything was hooked back up right. VOILA! Only code I got was the no power code. In addition, disconnecting the EEC for at least 15 minutes will make it relearn the fuel tables. Some of the tables are static, but, others are dynamic, and are adjusted based on O2 sensor readings. These are multipliers for fuel/air mix based on engine speed, O2 content, and a lotta other things. This is why the EEC can sometimes mask a real problem long after it's past time to repair it. There are limits, and yes, when the vacuum leak gets bad enough, you will get pinging and lousy mileage, but that may be two years down the road. I didn't know I had an intake problem on my F-150, and paid a dealership a LOT of money for an ignition tune-up that they didn't even have plug wires to complete. A vacuum gauge, fuel pressure gauge, and a little of my time and I have a sweet running truck again. Something the dealership never did accomplish. The FIRST thing they will do is disconnect the battery to see if the EEC has simply learned some bad habits, and to clear codes from any past problems that may have been repaired. But, since most of the guys in the dealer shops around here are little more than smart monkeys, don't know anything if it doesn't say NINTENDO or SONY on it, and don't know a box-end wrench from a dead-blow hammer, they have no idea how to really diagnose a system that likes to hide the real problems. I have some really nice photos of some dealer work with some "GENUINE FORD PARTS" made from the side of a solvent can or something. I can show you a LOT of things to NOT let a dealer do to your Ford.

CLUNK!

Now that I'm back off my soap box, disconnecting the battery WILL reset the EEC, but only if it's left disconnected for a minimum of 15 minutes. There are capacitors, etc, which will retain NVRAM power for a little while (enough time to change out a dying battery?) Even better if it's done and left to sit overnight. Trust me, if I do this to either the F-150 or the 'Bird, both get LOUSY fuel economy for the first 100 miles or so. Suddenly, the mileage will start climbing back to normal. This would be the EEC learning the fuel curves again. And NEITHER has ever had any stored codes when I reconnected, unless there was a real problem.
But, I must admit, the better way to clear diagnostic codes is to interrupt a KOEO test after the test starts flashing the codes. That guarantees a reset of the diagnostics codes, and retains the fuel curve data. The EEC will also sometimes signal an NVRAM fault after being powered down for any length of time. No biggie, just clear 'em with a KOEO interrupt. I like the number 11.
BTW, auto mechanics is a hobby for me, not a profession. I am an electrical engineer that specializes in digital control systems, with 25 years experience in the industrial world. The EEC isn't really that complex compared say, to a rolling mill that runs at 7000 ft/min and controls gauge down to .003 at those speeds.

Engine idle.

Reply #16 – February 22, 2007, 08:09:28 AM

Quote from: big Mike;129384

I have a problem with my 87, Cougar. The idle on my 5.0 is too fast, most of the time, and some times it's ok. I have checked my throttle, and cable, and replaced my throttle position sensor. The repair manual I have dosn't have enough information on this issue. I shure could use some help finding the cause. Thanks, Big Mike .

Your fast idle is probably caused by a vacuum leak. The reason (I read down before replying) you'd see the problem come back, is the EEC is adjusting for the lean exhaust. I have the 5.0 in my '92 F-150, EFI, EEC-IV, OBD-I. Bank fired, not SEFI. I haven't seen the intake on the car engines, but on the truck engine the intake sticks WAY up and over the right VC. There is an inherent problem with this design that the paper thin gasket between the plenum and lower intake will fail. This creates a couple problems. One, you get cross-flow between ports in the intake. Two, you'll probably pull in outside air too. This lowers the vacuum, which when sensed by the MAP, says the throttle is partially open, regardless of what the TPS is telling the EEC. Idle speed is where you'll have the highest vacuum, and the leak will be more significant. When the EEC is first powered up, it's designed to run the engine rich until it can figure out how much fuel it really needs to run. If we're lucky, it'll work out to a stoic 14.7:1 mix after all the cipherin and gazintas are done. The cross-flow between ports may rob one cylinder of air, making it run rich yet have another run lean. The O2 sensors detect a lean condition, the MAP sees lowered engine vacuum, so turn up the fuel. It will finally balance out to a nice fuel mix that the EEC likes, but will probably idle very fast, and generally there will be some misfiring unless the leak is fairly minor.

Get a good vacuum gauge from your local parts house and start hunting leaks. At idle, the intake vacuum should be around 20 inches of mercury (Hg). 18 is good on an old engine, more is better, less is very bad. Disconnect every vacuum line except the FPR and the MAP sensor, and cap off all the nipples. Start hooking them back up one at a time until the vacuum drops. You'll find your leak if the vacuum is good with everything disconnected. If the vacuum isn't at least 18 inches with everything disconnected, and the lines to the FPR and MAP are known to be good, you're looking at some wrench pulling to replace intake gaskets. I'd try the plenum gasket first, but don't rule out the lower intake gaskets, especially if you see any oil/coolant weeping around the intake. Yank the top off and you'll be able to see the lower better. It ain't a bad job. I had the plenum and throttle body off my 5.0 in an hour. Took more time to clean the injectors and throttle body.

One other thing could be the IAC is sticking open after the engine warms. If the car intake is anything like the truck intake, the EGR is right behind the throttle body. This cakes the backside of the butterflies and the IAC ports with carbon. This will cause the IAC to malfunction.

Oh, btw, a Ford Dealership Service Shop (a total of 3 of them in this area) couldn't find the cause of the sputtering, fast idle, and lousy performance on my truck. There isn't a joystick or keyboard port on it, so the smart monkeys couldn't find it. They didn't mind charging me a ton of money to try, though. You CAN fix this yourself, and for a LOT less than you'll pay a dealer. An intake gasket set will run you about $15. Vacuum hoses/tubing/fittings for the whole friggin engine shouldn't be over $30. You could replace everything on the top side of that engine for a lot less than a dealer will charge you to put in a set of spark plugs.

Engine idle.

Reply #17 – March 08, 2007, 10:31:54 PM

Thanks to all for the information. I will let you all know when I find the source of the Idle problem. B M.