Dustin Mustangs

iTrader: (1)

I am still trying to diagnose some pesky problems on my 'roc. The car runs fine, and still makes mudstains look stupid, but it's got a few quirks I am trying to work out (ie. rough idle, bad miliage, and an occasional rough start). Today I was sitting at idle, which is the only time my $hitty Auto-Xray will work, and I noticed a few parameters that were varrying quite a bit. First is the 'engine RPM', it varried between 540 and 660 RPM's (hence the ruff idle). Then I noticed the 'engine load' was all over the place also, from 40 to 51.

What is this 'engine load' parameter, and what sensors does it base it's info from?

I also noticed that my spark advance was varrying a bit too, from 19.9' to 27.6'. And to add to all this my pulse length was all over the place also, from 1.0 to 1.7 ms. Remember, all of this info was taken at idle and with a completly warm engine.

Any ideas as to what this should tell me?

Please help, I am so confused with all this...

Thanks in advance! :hail:

Jza

Engine load is basically how much work the engine is doing for how fast it's turning (loosely defined). Just think of the difference between 1500 RPM at idle and 1500 RPM cruising down the highway. You can tell this from the sound. The two sound completely different even though it's the same RPM.

Load is usually synonomous with vacuum and since your load figure is all over the place and you have a rough idle, I'd suspect a vacuum leak somewhere. Follow every single vacuum hose and check for dry rot and leaks. You can go leak hunting with a length of vacuum hose and a can of starter fluid or carb cleaner. Stick one end of the hose in your ear and probe around the vacuum lines with the other end listening for the thin squeal of a vacuum leak. If you lightly spray around the hoses and the idle raises some (more than it's already loping) that will also indicate a vac leak.

Dustin Mustangs

iTrader: (1)

...hmmmm, vacuum leak eh. I did some vacuum testing on my car this weekend to see if this might be the problem. The vacuum readings are also unstable, and varry between 17" and 18" at idle. My dad helped me and according to him those #'s are right were they should be (although he said the fact that it wasn't steady could indicate a leak), mind you his hay-day was during the 60's twisting wreches on the side of woodward ave. I thought I had heard that the vacuum on a mostly stock tpi car, like mine, should be a good amount above 20" at idle because of the conservative cam.

Is this right? If my vacuum is low, were are some of the trickier spots for vacuum leaks on our cars? I have already done the TB cleaner trick, and I also tried disconecting some of the vacuum related systems(breake booster, FPR, CC, ect.) and capping the lines with no type of luck.

Thanks for any help!

Jza

On both of my TPIs, I always had trouble at the thin plastic lines from the throttle body to the EGR solenoid. They'd get brittle and crack with age. I also had a lot of dry-rot right where hoses slipped over the nipples.

You could also check the PCV hose, as well as the throttle body plate gasket.

Disconnecting and capping the lines would only rule out internal vac leaks in the systems in question, not the lines themselves, which is what I would suspect.