Why does my '74 1.8 sometimes run so RICH?, After a bit of driving, it won't idle Options

[drdstny]

Hello many kindred,

So I drive my 914 every day, about 60 miles per day to be exact. Almost immediately, I noticed that (this is so hard to believe I'm having trouble posting) if the left engine heater hose comes off the heater blower, the car won't idle and will stall unless I keep the R's up above 2K.

So...I fixed that with some Tape.

Before I Taped it to the blower, it was predictable: if the car suddenly started running rough, rich, with smoke pouring out of it, then I knew I needed to put the hose back on.

Since I "repaired" the hose, now it's less certain. About halfway to work, once I hit traffic and have to stop-n-go, it idles rough. VERY rough, and I need to side-step the gas to keep the engine from stalling. Smoke will come pouring out of the tailpipe, my eyes water, can't breathe, lose faith in humanity, diet goes awry, idle won't calm down...you get the idea.

Seems like it only does this after about half an hour of driving, and USUALLY letting it sit for a couple hours will make the problem go away. Not always, but usually.

The first thing I tried was changing both seals (O-ring and gasket) on the oil cap (recall it's a 1.8), but that made zero difference.

So...anybody have any idea what's wrong? Just as good: anybody have a list of things I can test or replace until the problem is fixed?

This is a serious issue, and the last two tanks of gas have been sub-20MPG so I'd really appreciate the help. I'll send something nice to the person who gets me out of this jamb.

Thanks!

[Rockaria]

Could it be the Cylinder Temp sensor near the #3 spark plug going bad or loosing ground? I know that is directly related to rich/lean. It should be 2,000 ohms cold and about 56 ohms hot. If the wire is loose or comes off you get full richness, I believe. If the heater hose you refer too is on the passengers side it may be hitting and ungrounding the wire for the temp sensor.

I would start there... Then work towards the fuel pressure regulator near #1, and last but not least the AFM... Air filter clean? AFM not smooth..

Try those things...

[Cap'n Krusty]

Bad airbox. The Cap'n

[jim_hoyland]

Airbox

[bd1308]

what does "bad airbox" mean?

don't you mean AFM?

I am intrested in this.

b

[Dave Bell]

Airbox = AFM... what everybody said above...

If vane sticks in AFM, when you return to idle, vane is still open as if you were pulling more air through so FI pours in more gas...

AFM gone bad from old age or wacked with too big a hiccup that went backwards through the intake. There is a spring loaded port on the vane to protect from such back fires.

You can acutually, "catch" a sticky AFM in the car... when you are running rich at idle... stop the car...

Method #1: Then turn the key on but do not turn the engine over... fuel pump should NOT come on.... Fuel pump on the L-jet only comes on when the AFM vane comes off the closed position, i.e. when you are cranking the car... if the vane is stuck open, the fuel pump will come on with engine off but key in on position... if this is the case for you.... wrap/tap on the side or the AFM to see if you can unstick the vane... if it unsticks and returns to closed position, fuel put should go off.

Methond #2 Take out the AFM and see if it is stuck partially open.... or just take out the AFM, move the vane by hand and see if it sticks somewhere along its travel..

Bad CHT or disconnected CHT will make you run real rich... FI thinks the engine is super cold and pours in the gas.

Fuel pressure regulator would have to be pretty far off to make you run so rich it would hurt your eyes

[drdstny]

OK, good leads so far, lots pointing to the air box. Question is: does anyone have a known-good COMPLETE airbox for a '74 1.8 for sale?

Customer waiting.

Of course, if that's not it, I'll need to bill all of you in virtual beers.

[billswim]

I've got a couple but you need to see how many pins are on the plug. Some have 6 some have 7 (I think). Your problem doesn't sound like the air flow meter to me though. It doesn't make sense that it takes almost 30 minutes of driving. A stuck AFM should be the same all the time. your mixture would right at only one perfect throttle position. I've recently had trouble with the 1.8 fuel pressure regulators. Test the system to see what running pressure you have at idle and at part throttle. I forget the #'s but around 29 psi at idle and a few lbs more at part throttle. The temp sensor is also a prime candidate. If its grounding out, it would make the car go lean, not rich. If it was stuck with high resisitance (sp?) the car would think it was always cold and would put too much fuel in but not so much that your eyes watered. Also the 1.8s are SUPER sensitive to vacum leaks and if you have recently fixed a vacum leak, and the system was adjusted for the leak then the car would run too rich. Don't just throw parts at it. It'll cost way too much.

[Rockaria]

If I were to guess at one thing... The part that made me nuts on mine was a bad wire into the Head Temperature Sensor. At one point it was just lose enough that it worked unless you moved the wire and it would basically disconnect the wire temporarily and making it go full rich. Then I would touch it again and it would go back to normal. A new CHT and all was well. Heat at the head could be a factor, maybe. I also had a bad fuel pressure regulator. The vacuum part would work intermitantly giving it higher and lower fuel pressure at wild times. A new one and all was well.

Once I got all of my L-JET parts fixed and renewed it runs without trouble and has for years now, Knock on wood!

Just my extra thoughts.... (IMG:http://www.914world.com/bbs2/html/emoticons/beer.gif)

[John]

I think it is the air box. I think it is warping from old age and when it gets warm, it can get in a bind. I have seen 911 Carrera Air Flow Meters act sticky exactly like that.

It could be one of the temp sensors (or wires to temp sensors). If you have a break in the wire somewhere, it will be open circuit (infinite ohms) and will run rich.

I have a complete working 1974 1.8 fuel injection setup for sale now in the classifieds. (Good quality spare parts....)

[sean_v8_914]

I love L-Jet!

check the simple, cheap stuff FIRST. I too had an intermittent CHT wire. It did the same thing yours does.
christophers hot AFM check is simple to do also. if that pump is buzzing with the key on and engine off, the the AFM is bad. I do not htink it is AFM yet.

I live in san diego. you may borrow my AFM for testing. it is a known good unit

[drdstny]

OK, found that problem and created a new one.

On top of the engine, there's what looks like a secondary air valve of some kind. It has a big end with an electrical connector and a smaller end for a hose & elbow to slip on.

Looks like someone tried to pry ON the rubber elbow, because the metal part is cracked all the way around the bottom where it joins with the main body but outside the protection of the rubber elbow.

I guess what was happening is that once the engine warmed up fully, that crack would widen and Something Bad would happen. I snaked one from a junkyard 914, popped it on, and the problem went away.

However, now I have a different problem. Right about 3200RPM, the engine seems like it's out of gas, it just stutters really bad like it's starving (not lean, starving). The engine works fine, doesn't smoke or anything anymore, but this is a very drastic way to recover MPG, dontcha think?

Before I go buy a new secondary valve (thinking the one I got was no good either), I want to make sure I should. Apart from the richness issue, I never had problems going to 5,000 before, so I'm almost positive it's this thing.

Confirmation?

Thanks to ALL who replied, because that got me thinking and looking at simple stuff like I should have to begin with.