Embarrassing Confession

[ghnl]

OK, I have an embarressing confession to make. It took me 3 days of on & off searching to figure out the simple reason why our '84 Spider wasn't running right.

The symptoms began rather quickly - idle became rough, idle speed dropped from 950 to 650 rpm, and it would stumble on initial throttle opening. Once revved up to 2500+ rpm it would pull strongly to 5500.

My first thought was vacuum leak. I checked the intake air ducts and all the hoses. Didn't find anything amis.

I pulled the spark plug wires one by one and found that removing the #1 plug wire didn't make the idle worse. Removing any other spark plug wire did. I cleaned the spark plugs and swapped their locations - no change. I swapped plug wires - no change. I even replaced the cap & rotor (even though I had verified a good spark to #1). No change.

I checked compression. Good - 175 to 180 psi in all cylinders. Valve clearances all correct. I cleaned & tightened grounds.

Now I was thinking maybe I had a faulty fuel injector. I had sent them out for cleaning last year when I rebuilt the motor. Rather than just replace the injector I removed the fuel rail with injectors and had my able (and beautiful...) assistant crank the engine while I watched. All the injectors appeared to spray equally well. And not spray when they shouldn't.

Finally, with increasing desperation I decided to remove the oil vapor separator and clean it out (although I had done so last year before installing the rebuilt engine and didn't expect it to be gunked up).

Only when I removed the large hose at the top of the separator did I discover that the smaller hose - the one that goes to the intake plenum near cylinder #1 - was loose! It was near the fitting on the separator and looked OK but it wasn't snuggly attached. I know I had checked the plenum end. And looked at the separator end. But since my fat mitts wouldn't fit down in there, I hadn't actually tested that it really was attached. arggh!

Put everything back together and it immediately ran correctly.

[the_sicilian]

thanks alot for the headsup and illustration sir

[Greg Gordon]

Very good point. People often overlook air leaks from the air/oil separator. Those are just as bad as air leaks anywhere else. Even a loose fitting dipstick can cause a minor air leak. If you don't believe me, remove the dipstick at idle and note the change.

[Duke58]

Thanks for sharing your experience!

Duke

[Robert Ferguson]

I have the intake plenum off for starter removal, and while cleaning the plenum I noticed that the fitting which that small hose connects to was completely plugged with krud.
Bob Ferg

[Joe Papa Sr]

Quote:

Originally Posted by Greg Gordon Very good point. People often overlook air leaks from the air/oil separator. Those are just as bad as air leaks anywhere else. Even a loose fitting dipstick can cause a minor air leak. If you don't believe me, remove the dipstick at idle and note the change.

[Joe Papa Sr]

Quote:

Originally Posted by Robert Ferguson I have the intake plenum off for starter removal, and while cleaning the plenum I noticed that the fitting which that small hose connects to was completely plugged with krud. Bob Ferg

[MrT]

When we were troubleshooting our '86 Spider Graduate, I checked for air-tightness overall on the block and hoses by blowing into one of the small diameter hoses on the intake manifold. The large volume of the system means you can stuff a few cubic inches of air into it and then block off the hose with your finger to listen for small leaks elsewhere. If you have someone else with you, you can track down leaks you wouldn't find by yourself. We found a broken oil return line from the separater that way. Before fixing this line, the block would hold zero pressure. After fixing it, I could blow a few cc's (maybe) of air into the block and it would come back out a few seconds later when I took my finger off the hose. The system would hold NO overpressure even as long as a second before replacing that hose. So you can do a check that tells you whether 1) Everything Is Tight or 2) Something Is Leaking in the manner described. Finding what Isn't Tight is still the problem, but knowing that everything is OK is a worthwhile thing.

Michael

[redspiderveloce]

I'm glad you found the problem. I never would have thought that one of those hoses would cause the car not to start.

[MrT]

Wellll. the hole in the hose didn't actually keep _our_ car from running. I was just recounting a debugging technique that I had used successfully for checking on LJet hose systems. That car's problem ultimately turned out to be that a P.O. had over-leaned the AFM and the car was running chronically lean. He _may_ have been trying to enrich the mixture, but it ended up lean. Greg Gordon's LJet pages pointed me in the right directions for fixing our problem, and along the way I used the "is it tight" test I mentioned above. It wasn't, but I made it so. However, tightening it up didn't help much.

Michael

[mrutkaus]

That's OK, I once rebuilt a Sirroco engine because of a loose carburator screw.

Mike

[WIP]

Any good tips to keeping the dip stick in place... I have an '84... after driving so many miles, I'll get an occassional hard start (not really a big deal, but noticable)... look under the hood, yup, dipstick has popped up half an inch or so... push it down again... more 2-3 second crank... cranks immediately. Now, how to keep it down. (-;

[velocedoc]

Good description of how you traced all of the possibilities. Everything has to be secure.
side note: Our spider wouldn't idle when I first put it on the road and was blowing oil out the bottom of the air box. Turns out that the oil separator was plugged full of junk. Fixed it (1/2 hour of tapping to get it all out) and checked the oil return line and now everything is perfect.

[ghnl]

Quote:

Originally Posted by MrT When we were troubleshooting our '86 Spider Graduate, I checked for air-tightness overall on the block and hoses by blowing into one of the small diameter hoses on the intake manifold.

[MrT]

But you didn't say whether it actually helped! So. Are you "on the road again?"

Michael (gleeful at being of some actual help to some actual person)

(_Nice_ pics, by the way.)