Engine Idle Update

[Dave Bell]

I had a problem before with engine idle... see past post, 2/20/2000, Especially after the car had been stopped for 5-15 minutes, I would go to start it and it would not idle at all... so I had to set the idle adjustment screw way too far open, running a high idle 1500 rpm, to "fix" the idle drop out under these conditions.

Both Pritchard and Alexander suggested that I might try adding a 500 to 700 ohm resistor in line with Cylinder Head Temperature Sensor....

Well I got busy fixing some rusty floor boards and putting in new carpet so I never got to completely finish sorting out the idle thing... But I needed some solution... so I thought, why not permanently put a dash mounted potentiometer in line with the Cylinder Head temperature sensor. So I picked up some teflon coated wire, (very resistant to heat), and ran a connection from a 1000 ohm pot I installed in the dashboard just to the right of the lighter and connected it in series with the Cylinder head temperature circuit back in the engine bay.

Now I have means to dial in a little richer mixture of gasoline to smooth out the idle... and I can dial it out for highway driving... Heck I can dial it in and out anytime I want now for that matter.

I still have a couple more items to check in the fuel/throttle circuit but this "fix" has been quite useful for me. I was able to close down the idle adjusment screw to a reasonable value and I can set my idle now and move it up or down at will... right from the comfort of my drivers seat.

The only downside I can think of is forgetting to dial out the extra richness, which could only make the engine run, cooler?, smoggier?, potential deposits on the plugs?,... others may want to comment.

In any case, it was so useful for me, that I thought I would post my modification and the results. One change I might make is to replace the 1k ohm with a 2.5k ohm pot to get a larger range of adjustment... I have not tried that yet but I probably will. Since I can't find a 2.5k ohm pot, a 5k ohm with a 5k or so fixed resistor in parallel with it will also do the trick for those interested. Or just use the 5k ohm and alone and have a more sensitive adjustment scale.

I wonder if others have put in inexpensive dash mounted FI adjustments or monitors.

Thanks all.

- Dave

[tmk]

Dave: A bigger problem is running to lean. You run the risk of burning valves and pistons or dropping a valve seat.(very bad) Running to rich may wash down the rings and bearings was well as fouling the plugs. Get a air fuel ratio meter so you will know that all is OK. Less than $100.00. I got one from CB Performance.

TMK
73 914S 2.1L

[Joe Bob]

O2 sensor is a good idea. They plug into the exhaust manifold. You can put the gauge in the center console (assuming you have one) and replace the clock that never seems to work...most don't need the clock if you have a newer radio with one....

[Alpine]

Dave,

In the March 2000 issue of Hot VWs there is an article titled "Straight to the Top" that describes the installation of a Mark Stephens top end kit on a Vanagon Type IV motor. They also plugged a potentiometer into the EFI system and installed an air/fuel gauge. Anyway, adding an in-cockpit potentiometer and air/fuel gauge to monitor and adjust my d-jet system is something that I'm seriously considering when I'm sure that my fuel injection system is working properly and everything is within spec. Please keep us posted on your car's driveabilty, mileage and any other pros/cons of adding the pot to your cylinder head temperature circuit.

Thanks,
Alpine

[Germain]

These air sensors, where do they go on the exhaust? I have dual exhaust, and the two sides never come together. Would I need two, or is measureing only one side give a exact description of the other? Any input would be great. Thanks

[Dave at Pelican Parts]

You have two choices with a dual exhaust. You can either read one and "assume" that the other side is identical, or you can install two sensors and two gauges.

I have a sensor installed in one of my pipes. These are stock-type heat exchangers, which don't come together until they are in the muffler. I am assuming that the one cylinder is representative of all four. Not the best assumption, at all, but the only feasible one for me.

Actually, now that I have a Bursch, I can install the sensor in the collector. But I'll have to plug the hole in the exchanger...

I got the three-wire kit from CB Performance for $176. I figured that the simple one-wire would take FOR EVER to give me a reading, since it would be kinda far from the heads and might take a while to heat up. I still don't trust the readings all that well, but at least it does give me *some* readings.

--DD

[Joe Bob]

OR....you can install a cross over pipe...quiet the exhaust, help on "scavenging", allow for one sensor...

[Dave Bell]

The O2 Sensor and monitor sound like a good idea.

I located it at: http://216.111.121.85/cb/catalog.asp?ProductID=598

on the CB Performance Site.

Cost is only $114 for the "kit".

I would like to know a little more about the procedure for installing this before I order it.... drilling, welding.... what will I have to take apart and watch out for?

I don't have a center console so I'll have to find some place else to put the meter.

Comments?

[tmk]

I have the one wire from CB Performance. It starts to work after about 3 minutes. I put it in the collector of a Bursh. Get the
Adapter Pipe w/Threaded 18mm Adapter welded in.

TMK
73 914S 2.1L

[Dave Bell]

TMK -

What is the difference between the "Adapter Pipe w/Threaded 18mm Adapter welded in" and the "Threaded 18mm Weld in Adapter" if you know.... it looks like the kit comes with the , "Threaded 18mm Weld in Adapter" and the adapter pipe you are recommending costs more.

- Dave

[Harold Hedge]

Oops

[This message has been edited by Harold Hedge (edited 04-06-2000).]

[Harold Hedge]

Dave,

Check out this CB Performance pdf page in the Tech pages, http://216.111.121.85/cb/pdf/AirFuelRatioMonitor.pdf the adapter is a jumper piece.

Harold

[This message has been edited by Harold Hedge (edited 04-06-2000).]

[This message has been edited by Harold Hedge (edited 04-06-2000).]

[tmk]

Dave: With the adapter you can weld or bolt it to the collector. The other way you have to make a hole in a pipe and weld it in.

TMK
73 914S 2.1L

[Dave at Pelican Parts]

You're assuming that the exhaust has an appropriate place to bolt on that short pipe. Few do.

Look at the pipes in the illo; the system is intended specifically for Type Is. For a Type IV, the easiest thing to do is just use the fitting that comes with the kit. You'll have to do some welding regardless--so it's not any tougher to have the little part welded in than the larger part. (The larger one being that whole tube.)

IMHO.

--DD

[JP Noonan]

My understanding about the heated sensors: A car puts out a large portion of it's polutants before the motor warms up and the cat's "light off". To help reduce this the manufactures use heated sensors so the engine goes from "open loop" (no input from a O2 sensor, like the 914) to "closed loop" faster. If it takes "forever" for your single wire sensor to show readings I'd say it was too far back in the exhaust.

[Dave Bell]

I got to looking at the exhaust connections under my car this weekend, and I think Dave Darling is right, (big surprise.. right!)... it looks like more work to put in an adapter pipe than just to drill a hole somewhere and weld in the simpler threaded ring piece.

It will be awhile before I put in this mod though as I really would like to make the idle work right in the first place... The dance continues...

[Germain]

Okay, I've done some ivestigative work, and here is what I've found. The Oxegen sensor compairs the air on the outside of the axhaust to the air on the inside of the exhaust. By measureing the differance, it displays 0 to 1 volts. 0 being lean, and 1 being rich. .5 volts is (cant remember word, striff?) buts it's 14.5:1 ratio.

With this in mind, the sensor does not start working until it is 600 degrees, a heated one will do it in 1-2 minutes, and non heated in 2-3. The only thing they are good for according to what I've read is during normal driveing conditions. When you accelerate, the car should burn rich, under deceleration it should be lean.

Okay, now how can you make one, or do you buy it. Well you can get a single wire Bosch unit, about $25 at any parts store. you can then get $30 in simple electronics to display a light patteren (need to have some electrical mack ground), or you can hook it up so some simple volt meter. Or you can get some fancy guage to replace the clock that will never work again (this is what I am doing). Total price on my O2 sensor and guage, $75.

Hope this helps.

[surfcity914]

where on the heat exchanger is the best place to mount the oxygen sensor? i have stainless steel heat exchangers. will the muffler shop have to do any special welding for stainless steel?

[scriabin]

In response to the above post, Yes. I had to go to a shop which could specifically weld stainless. I had the threaded bung welded to the top of the exchanger pipe for #1, so that the unit pointed straight up, clear of any obstruction, immediately behind the boxed portion of the exchanger and before the bolt-on exhaust system.
I used a home-made gauge built from radioshack componentry, and a pretty round gauge purchased from a race shop, as a comparison. However, as I am running dual carbs, I found the appliance rather useless for my application, and disconnected it. So now I'm just glad that sensor never gets in my way, at least.

[tmk]

It has to be were it can read all cylinders not just one. I put it in the collector of a Bursh. I have dual Webers and it works fine for me. I have the one wire unit and it starts to work in about three minutes. At WOT it reads 12+ to 1. At cruise it reads about 14.5 to 1. When backing off from WOT it reads about 17 to 1. It works very good if you put it in the right place.

TMK
73 914S 2.1L