"Cam Lope" Sound in 5.8 efi

[90windsor]

When i go to start it up in the morning, if i give the gas a quick tap, it will come down from the "cold start high idle", idle at about 500 rpm and have a really nice sounding "lope". it will only last about 30 seconds, and go away as soon as i give it any gas. just wondering if anyone knows what im talking about or why it does that. theres nothing wrong with my motor, i was just wondering what the mechanical reasoning is behind that.

also, before its warm, if you rapidly tap the gas it will also sound like it has a cam (most trucks will do this) just wondering if that is related.

i hope someone on here knows what im trying to explain, because it does seem kind of goofy.

i does the same thing if you run it without the map sensor vaccum line

 

[chuckles1856]

Hey 90windsor,

I was somewhat reluctant to reply cause I don't have a good answer for you; however, I think I know what you're talking about. My '91 would do the same thing, I think. When I'd let it warm up it would idle high. Sort of a like if you would slowly press on the gas and slowly let off and repeat it until it warmed up.

Then eventually it would "kick down" and get to that "lope" you talked about. I was noticing it more lately, before I noticed it had a leak and I torn into it, that after I let it warm up and I'd drive around a bit it would go back to a high idle. Sometimes I'd try to manually "kick it down" by tapping the gas quickly. It would then drop to a low idle but it would usually go high again.

 

[BroncoJoe19]

90windsor,

read this.

http://fordfuelinjection.com/?p=64

you might have the pCM puking trying to figure out which strategy it is supposed to be using at the time.

chuckles1856,

loping idle is often a dirty IAC, or vacuum leak.

high idle is often a vacuum leak

less often a high loping idle is a faulty TPS

What does the IAC do? How does it work?

http://www.fordfuelinjection.com/?p=39

Check and clean your IAC

http://www.ford-trucks.com/article/idx/8/1...er_IAC_Fix.html

Tips for Checking for vacuum leaks.

Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.

Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

Another suggestion is: to take a propane torch, turn it on (but don't light it) and move it over the vacuum hoses and connections. The engine RPM's will increase if there is a leak and the propane gets sucked in.

Courtesy of TheOldWizard ford-forums... Don't forget to remind folks to check the PCV valve, hose and grommet !

Courtesy Ramnasal ford-forums... Clamp off the hose that runs to the vacuum booster (brake booster) or pull it and plug it. It is possible that the diaphram on the inside of the booster may go bad and cause a vacuum leak.

 

[chuckles1856]

Thanks BroncoJoe! I'll be replacing lots of stuff as I've got the lower intake off at the moment. While I was disassembling to get to it I noticed certain hoses and wires that didn't look quite right. When ever I get her back together I'll report on how she's running.

 

[tiller83]

90windsor, ultimately your engine computer is still in warmup until the desired temp is reached.most people don't (won't) wait for it to completely warm, so whene you hit the gas ,or sometimes break to shift, it drops the mechanical (vacume) portion or ignition advance for the fastidle to prevent a slam on the drive train (trans). but in order to continue warming up it is over fueling (choke). thats the gutteral rumble of to much fuel, mine is carbureted and does the same thing but i have to wait longer for it to fix itself, the computer in yours is resseting the idle once it senses the mistake. mine used to sound just like a race car, now it's just loud,or i'm getting old.