Fuel injection issue

2-73vdubs · Posted: Fri Apr 13, 2012 9:55 am Post subject: Fuel injection issue

I test drove a 1979 Super last night that still has the fuel injection in place.The car starts and idles perfectly normal but when you drive it,it hesitates under load.You have to give it a lot of gas to take off and it has a skip or miss going through the gears(especially 1st and 2nd).Once it gets up to speed it runs smooth.I drove it for about 10 miles on the interstate and it held 60 mph pretty easily on flat ground.Any ideas why it hesitates under load.

Randy in Maine · Posted: Fri Apr 13, 2012 9:59 am Post subject:

Could be a number of things including "munged up" injectors or injector seals that are leaking vacuum.

Did the car just sit for a while (like months)?

2-73vdubs · Posted: Fri Apr 13, 2012 10:05 am Post subject:

According to the seller it sat up for about a year.The injectors are new and he has paperwork for other work that has been done on the injection system.He said the entire system was gone through,and everything looks really clean, but he said he made some adjustments and now it is running rich.
I also noticed that the gas pedal is really hard to press down.

Randy in Maine · Posted: Fri Apr 13, 2012 10:18 am Post subject:

This thing should actually do about 85 MPH wide open.

If you are really interested in this thing, do a proper compression test, check the ignition system, valves, fuel pressure, and the throttle cable to see if any of those are the hold up.

EVfun · Posted: Thu May 03, 2012 9:41 pm Post subject:

I have some issues with my FI being a bit rich too, I haven't gone through every part of the system yet so I don't know where that is coming from. I have a bit of a low idle speed about 1 minute after starting until fully warmed up.

The manual I have indicates that hesitation can have a couple of causes.

1. With a warm engine the resistance of the temperature sensor on the head should be around 2500 ohms (2.5k ohms.) If it is significantly different (what is significant isn't specified) it should be replaced.

2. The EGR valve is open or partly open at idle. If this is the case the pipe should be warm after idling for a while. The valve should be open only at mid throttle ranges and closed near idle and near wide open throttle. If the ignition switch is on but the engine is not running you should be able to hear the valve click on and then off as you slowly open the throttle all the way.

In addition to these FI specific issues a weak ignition system can cause hesitation. Air leaks that lead to a lean condition can also cause hesitation.

75smith · Posted: Thu May 03, 2012 9:52 pm Post subject:

being rich could be from the cold start valve(basically fifth injector) leaking

or they played with the airflow meter-if set incorrectly it may let in less air than the engine needs
_________________
My 1975 Beetle Build Updated 8-21-12

My engine build

EVfun · Posted: Thu May 03, 2012 11:39 pm Post subject:

Good call on someone messing with the fuel mixture -- the plug wasn't put back in to cover the adjusting screw.

As a hunt on this '79 around I find a couple other things I don't see on the drawings.

1. There is a manifold vacuum line, attached to the same port that the decel valve and EGR valve are connected to, that goes around the back of the fan shroud on the right side (behind the air cleaner so I had to follow it by feel.) It looks like it is heading for the starter, but ends at some small can back on the rear engine tin, the upright part that the dog house oil cooler vents through on the other side. What is it?

2. There is a loose female 1/4 inch spade terminal back there too. The wire color is black as near as I can tell with the limited view. Any idea what that is? This is a running car that generally drives pretty nice.

string · Posted: Fri May 04, 2012 2:22 am Post subject:

It is the fuel pressure regulator.

TromBug · Posted: Fri May 04, 2012 4:17 pm Post subject:

I think the black wire coming from that back corner could be for the reverse lights. There should be a black wire coming off the coil which leads to an inline fuse holder, which should then continue to the connect to the wire you described. I remember being confused as to why that wire was coming from back there too. It still seems like an odd place for it. I believe it's like that though so that the reverse lights only get power when the engine is running.

2-73vdubs · Posted: Fri May 04, 2012 4:43 pm Post subject:

EVfun · Posted: Fri May 04, 2012 4:56 pm Post subject:

Thanks about the fuel pressure regulator String.

The reverse light fuse is blown and the wire shredded behind the throttle body so that is possible. There is also a black wire from the TDC flywheel sensor and it could be that. Thanks Trom.

Now I have question about vacuum lines for a '79 F.I. engine. I have the duel vacuum distributer and a fuel pressure regulator to connect. Which one of these is correct:
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

or

In both images the line on the front of the distributer vacuum can goes to the back of the throttle body. Every picture and description I found indicates that.

In the first image the vacuum port on the front of the throttle body goes to the fuel pressure regulator, EGR, and decel valve. The vacuum port in the intake manifold goes to the back of the distributer vacuum can.

In the second image the vacuum port on the front of the throttle body goes to the back of the distributer. The vacuum port in the intake manifold goes to fuel pressure regulator, EGR, and decel valve. My car currently matches the second image but enough has been disturbed that I don't trust it to be correct.

Oh, how am I supposed to pull the air cleaner out? I can unclip and shake and wiggle to remove (and install) it but there must be an quicker procedure.

CORRECTION: "In both images the line on the front of the distributer vacuum [...]" was "rear" and that is wrong. I screwed up the second paragraph description too, it is fixed now. Embarassed

J. Random Hacker · Posted: Fri May 04, 2012 5:43 pm Post subject:

The vacuum port on the front of the throttle body (up high) connects to the distributor. The vacuum port on the side of the throttle body just above the intake manifold connects to the intake decel valve, fuel pressure regulator, and probably the EGR valve (mine is a CA car so it has a mechanical EGR valve linkage).

If you talking about the air filter element...small hands. unclip, and wiggle to remove. If your talking about the whole assembly, there are two 10mm(?) nuts on the top holding it up, and 4 bolts connecting it to the air flow meter.
_________________
78 Super Beetle Conv. (FI)

EVfun · Posted: Sat May 05, 2012 2:17 pm Post subject:

Thanks, I made that change. The concept that the distributer is connected front to the back of the throttle body and back to the front of the throttle body is the most common all around the web. I connected the fuel pressure regulator to the low fitting and didn't connect the EGR and decel valve as those lines won't reach. I took it out for a drive and it runs nice, I can't feel a change from swapping the lines but just before I swapped the lines I tested the operation with the EGR and decel valve disconnected (the concept is to make only 1 change at a time.) That lowered idle speed so I suspect somewhere in those old lines or fittings there was a vacuum leak.

I think it would great if there was a sticky, or at least a single thread, where information about the stock AFC fuel injection system knowledge could be collected and shared. Every time I search before asking another question about the system I choose slightly different terms and end up with a different collection of posts to check. Overall, it seems to be a good system that had the misfortune of getting tangled up with some smog equipment.

finefettle · Posted: Sat May 05, 2012 5:48 pm Post subject:

There is a FI section in FAQ section yes? Not sure if vaccum lines are covered.

EVfun · Posted: Sun May 06, 2012 10:31 am Post subject:

The posted AFC manual covers the fuel injection but not the smog equipment that is tangled up with it. The orange Bentley manual covers the F.I. and smog equipment but is has few pictures or diagrams. It is more about procedure. I couldn't find a good picture of the vacuum lines in the posted manual or in my orange Bentley manual.

After some more hunting I found this samba thread about the vacuum lines and good information about the F.I. system in general. The first post, by Oldie_but_goodie, has an clear diagram of the Beetle vacuum lines. My system is now just like that except that the EGR and decel valve are not connected. I'm am seriously thinking about ditching the smog equipment and retaining just the fuel injection. It would make working on the engine easier.

finefettle · Posted: Sun May 06, 2012 1:45 pm Post subject:

Thanks for the link. If you live were they don't smog test you as I do, why not? I would hang on to it though as you never know with laws changing all of the time.

2-73vdubs · Posted: Mon May 07, 2012 6:51 pm Post subject:

OK,this is getting really confusing now.I changed the rotor button and distributor cap today and it ran great.I had also bought the points and condensor when I bought the cap and rotor so I decided I would go ahead and change them too.After changing the points and condensor it started missing again.So,I put the old points and condensor back in and it is still missing under load.I dont understand why it ran like it should after changing the cap and rotor but now its missing again.
Is it possible that I went too lean when I adjusted the air/fuel ratio and that is causing it to miss?

Randy in Maine · Posted: Tue May 08, 2012 2:21 am Post subject:

Did you ever test or change out the Temp Sensor II?

The resistance decreses as the engine warms up....

Image may have been reduced in size. Click image to view fullscreen.

2-73vdubs · Posted: Tue May 08, 2012 5:34 pm Post subject:

All I've done is a tuneup,valve adjustment and oil change.I have some receipts from where the injection system was worked on last year.One of the receipts say's "remove head temp sensor seat and clean,reinstall seat and sensor(now reads 1800-1900).I have had a lot of VW's but this is my first fuel injected one so this is all new to me.

2-73vdubs · Posted: Tue May 08, 2012 6:14 pm Post subject:

Oh yeah,I found a hose that is unhooked today and I cant figure out where it goes.It is the hose that comes from the bottom of the canister in the passenger's wheel well.

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