More FI issues - surging idle

[DJ]

Now that I have all the wiring tied back up nice and neat and everything connected as it should be, I find I have another problem.

The engine now starts and runs very nicely when revving. However, at idle, it surges between about 1100 RPM and 1800 RPM.

None of my troubleshooting guides address this problem. Does this sound familiar to anyone?

[rossocorsa]

are you absolutely certain that there are no air leaks from cracks in the rubber tubing after the airflow meter

[Jim Keller]

I dont' know what your system is configured from, but that symptom has always been the large screw in the plenium needed adjusted to bring the idle down, at 1100 RPM, the idle circut is kicking out thinking you have your foot on the gas, when that happens and it isn't recieving any signal from the TPS ot AFM, it shuts off the injectors for the idle circut and it starts to stall, the the idle kicks back in and shoots the revs up to 1500 or more RPM then it shuts off, trys to stall then shoots up again until you get the idle down by adjusting that HUGE FREAKIN screw, and ONLY do it on a totally warmed up engine, DO NOT adjust it on a cold engine.

If you do not have the Beta Plenium, L-Jet setup, I am clueless! LOL

[DJ]

are you absolutely certain that there are no air leaks from cracks in the rubber tubing after the airflow meter


Nope. I'm not. I've had the air tube off and back on several times so it's possible it developed a cracked.

I'm traveling on business all week so it'll be Friday before I can do any more trouble shooting.

[DJ]

I dont' know what your system is configured from,

You should know, Jim. You sold all the parts to me! LOL


but that symptom has always been the large screw in the plenium needed adjusted to bring the idle down, at 1100 RPM,

So now I've got two opposing opinions. My idle screw is turned in far enough that I can't turn it further without binding the butterfly. (See my other post about it.) It's not all the way in but any further and it will foul the butterfly. Will says it's in too far (not with regard to the surging problem, though) and you think it may be out too far. ::)

One other suggestion from another forum is that the O2 sensor could be bad or too cold. Even though my sensor is new AND 3-wire/heated, this is an interesting suggestion because when I first got it running right I didn't have the sensor connected and I'm pretty sure it idled fine then. In fact, it didn't do the surging even with the 2 bad injectors.

This and potential air tube leakage are the main things I focus on first when I get home on Friday.

Thanks for the suggestions.

[1,6 HF]

Ordinarily, I'd second rossocorsa suggestion; typically 'hunting' at idle is an air leak downstream of the carb (or in this case the metering).

But if it idled fine with the O2 sensor disconnected and is now surging with the sensor hooked up, sounds like the first thing to do is to disconnect the sensor and see if this improves things. If it has no effect, then my money's on an air leak.

[Will]

I posted this in DJ's thread about the idle screw, but I think the fact that he's got to run the idle screw way in indicates that the air leak is not in the air meter hose, but rather south of the throttle plate. There are a couple of little vacuum lines on the top of the plenum and a few other spots air can enter like the phenolic intake plate/gasket and underneath the TB. There is also the possibility of a leak in the breake booster line or primary diaphragm that's allowing the engine to draw air through the booster circuit.

Trying to diagnose, I'd clamp off the little lines at the pleunum, listen for a hum at the booster, and run a propane test thru the air intake as the first three items. At least, that's the armchair-mechanic's checklist! ;)

Hey DJ, when are you gonna ditch that idle air screw and put in a remote valve so you can adjust your air like a human?

[DJ]

Hey DJ, when are you gonna ditch that idle air screw and put in a remote valve so you can adjust your air like a human?

Probably when you offer a kit! Got no damn time for anything lately and the rest of the month already looks shot.

I hadn't considered the possibility that this powerful new engine might have sucked the diaphragm right outta the poor old booster. Thanks, Will. May need a kit for that too.

[Wallace]

Sounds a bit strange, but a length of hose with one end in your ear and another moved around the engine is very useful in pinpointing leaks !

[Will]

Clamp with two blocks of wood on the booster hose will isolate the booster easily. It's a relatively soft hose (provided it's not old and dry).

Remote valve: IMO well worth the effort. It's a real convenience on the Scorpion FI conversion, and practically mandatory if you want to implement IAC from a more advanced FI system. All you need to do is plug the port in the TB, and add a 1/4" ell with a hose barb and a remote valve that pulls metered air. If you put in a 1/8" petcock (same as in the block for coolant drain), just tighten the packing down enough the thing doesn't move easily. Or if running a modern FI with Idle air stepper output, simply take the remote IAC from a Maxima, etc. and throw that in. VRoooom!!!



Here's the real simple mod of the TB- the TB in this example is the stock one:
http://www.savetheledges.org/test/AVS/images/fi/scorpfi.jpg

The only inconvenient part is that you need to dismount the TB, but if you may have a leak under it anyway....

[DJ]

Well, there's no air leak that is obvious. Here's the results of my investigation so far.

It's not the oxygen sensor.

The air tube is really solid and nicely pliable so I'm not worried about it cracking and developing leaks.

It's not the brake booster diaphragm.

There's no open holes in the plenum. All have been plugged well.

The only thing I can figure is that the thin card-stock gasket under the TB is leaking. It's very slick on the surface, really thin, and I used no sealant on it. I'm going to make a new gasket from some thicker material and see if that helps.

I already took the throttle body off so I'll probably remote the idle screw while I have it handy. I'm trying to come up with an idea for a readily available valve that I can use. Not sure I like the petcock idea.

Suggestions?

[Will]

I found an icemaker saddle tap valve (1/8") was not really big enough- the problem is that it has a tiny hole that really doesn't flow enough to keep the 2L idling. Something like this ought to work better:

http://cgi.ebay.com/Parker-Needle-Valve-Instrumentation-Flow-Control-NIB_W0QQitemZ290146493044QQihZ019QQcategoryZ87087Q QssPageNameZWDVWQQrdZ1QQcmdZViewItem

-Will
PS> Presume you clamped off the little vac hoses on TOP of the plenum too? The Weber BB TB you have also comes two ways- with the 5th injector on the body or with a ported vac takeoff, make sure you don't have a hole where the ported takeoff is supposed to be!

[DJ]

All the ports on top of the plenum have either a hose connected or a cap on them. The TB has been modified to add the vac port above the cold-start injector so I can use the vac advancer on my dizzy.

[DJ]

OK, I now have a new question.

I've come up with what I think is a fairly clever solution to a remote idle adjustment that won't look like something out of my bathroom plumbing. (Now I wish I still worked in the shipyard or back in the power plants because I could easily procure a nice little needle valve or variable restrictor.)

But, before I go screw up the idle adjustment on my TB, I need to ask one thing. Does it matter where the air comes from? Specifically, the air for the idle adjustment screw comes from inside the air tube AFTER it's gone through and been metered by the AFM. Unless I'm misunderstanding all the suggestions I've seen for a remote adjustment, the air for such an arrangement will be external and NOT have been metered through the AFM.

How significant is this, if at all?

[John Allen]

anywhere after the AFM to anywhere after the throttle plate. IIRC the AC idle up is tapped off of the rubber duct pretty close to the AFM and uses one of small vacuum ports on the manifold near the #4 injector.

[DJ]

Thanks, John.

That's pretty much what I figured but wanted to get confirmation from someone smarter than me. ::)

[Will]

DJ- you want to use air that has gone through the AFM- otherwise you need to screw around balancing the bypass air circuit in the AFM. See my easrlier post. The easy place to get the metered air in my book is from the existing IAV, just tee in upstream of the IAV.

You could even tie across the IAV and just plug the TB, but this is making a design change away from the TB, and there would be no established flow through the TB around the throttle plate which could render the 5th injector useless.

Cut from your home plumbing? Boy, aren't you picky for a guy whose car ain't runnen' :)
Ebay needle valve and get yourself a nice Parker or Aeroquip stainless steel one. They are only about five times the price and a lot less flexible if you want to modify them. On the one I used a saddle tap needle valve on, I just dropped the thing in a warm bath of that Caswell electroless nickel and it came out nice. It was soldered to a brass 1/8" nipple off the TB, as a nickel plated assembly you would never know it wasn't stock. Actually, you would, 'cause it was about 10 times better looking than the stock Playskool chromate screw.

[DJ]

Cut from your home plumbing? Boy, aren't you picky for a guy whose car ain't runnen' :)

Now that's not at all fair. My car IS runnin'. It's just not drivin' yet. :-*

I only said that because the only readily available valves I thought MIGHT work are water valves from the plumbing section at Ace and Home Depot.

The good news is that I'm pretty sure I figured out why it's surging. When Steve Garran and I were troubleshooting the previous problems, I wondered why in the world the crankcase vent wouldn't constitute a significant air leak. Turns out I was onto something.

After someone on another forum mentioned the calibrated orifice that's supposed to go in that line, I had an epiphany. I had wondered where that thing was supposed to go. The reason I didn't know it was supposed to go there is because I happen to have one that was in a bunch of miscellaneous parts I procured somewhere along the way. I didn't have one in the FI system I had obtained separately so I didn't connect the dots and the diagram I've been referring to doesn't clearly show it there.

As soon as I am home long enough to find that part and install it, maybe I'll have some real success to report.

[Gregory Smith]

I'd be surprised if that solved it.

The crankcase should be a closed system, so it really doesn't matter if that orifice is in place. I removed it from my car when I had it, to prevent crankcase over-pressurization (if you have an old engine). No change in the idle for me.

The only way that could represent a vacuum leak is if your dipstick isn't sealing tightly. Sorry I couldn't be of more help, it's a real stumper. :-\

[DJ]

Thanks.

I'd think that the crankcase has more inward air migration than one might imagine, though. For example, there's always going to be some blowby past the piston rings no matter how new they are or how well they seal. I'd think that's why they put that orifice there in the first place. It will only allow a small, calibrated amount of air into the system and this amount can be accounted for in the design.

Regardless, I'll find out as soon as I can get to work on it again. It may be another couple of weeks, though.

Interesting that it made no difference on your car, though.

[Will]

It's been a while since I last looked at a Beta FI, refresh my memory- where does the crankcase vent tie in? Isn't it NORTH of the throttle plate (it should be, but Lancia have done odd stuff )

This should not be showing up as a vacuum leak. Ideally, you'd want the crankcase vent in the airbox, but Lancia (or rather FIAT may have decided it would crud up the Bosch AFM and located it downstream of the AFM, so again, where is it?

If the "restrictor" you are talking about is a plug that is convex or cone-shaped on the engine side and has a hole about half the diameter of the tube in it, I don't think it is supposed to be a "restrictor". I think it is supposed to stop oil that is atomized and made it through the cyclonic trap and sticks to the tube from migrating up the tube as a sludge (the oil moves along the side of the tube, not up the middle, so the cone acts like a scraper and dams it up before it gets to the airbox and/or AFM or carb). Presumbly when the engine stops the oil drains back down, but apparently not all of it since there is usually a nasty puss of grime and carbon-blackened oil around the engine side of said "restrictor".


That's my theory anyway. I think it's much more likely you are pulling air from the vac takeoff on the carb or something. I don't screw around hunting for stuff like this, first thing when I get a buggery idle is to drag over my B-tank and feed the car some gas and see what she does. That way I don't spend hours looking for a vac leak that turns out to be an ignition problem. Well, usually anyway :)