1981 FI swap to carb?

[emosfiat]

I need advise. Has anyone attempted to swap an FI system to standard single carb. If so what, if any, were the complications. I have had it with the intermittent poor running,missing crap. I figure if I get rid of the FI and the car still has running problems then I can trace it down to ignition or electrical. Now, I don't which way to look at. One day it runs great and the next it won't pull itself out of the driveway. Just a thought, anyhelp would be great. Thanks


Emo.

[mbouse]

an awful lotta work to go thru to diagnose an intermittant issue, isn't it? changing fuel delivery systems isn't gonna necessarily fix your problems... but changing the head and all that other related equipment just might accidently remove the source of the issue in the mean time.

whether F.I. or carb'd, you should be able to locate the source and eliminate the malfunctioning system. i'll let the F.I. boyz defend their systems, but i am betting you're not hitting the nail on the head with your cure.

[rlux4]

Mike is right. (Go figure! )
Before you go to the trouble and expense of swapping out to a carb system, I'd recommend that you keep trying to get your FI system sorted out. Once they're in specs they are very easy to maintain and reliable.
A few things that could cause an intermittent problem:
A faulty ignition switch, or poor connection at the connector behind it. (Check the condition of the pink with black wire.)
A faulty inline fuse, or fuse holder on the brown with white wire up behind the fuse panel. The original clam shell type fuse holder on mine would intermittently loose good contact and it was very hard to diagnose.
A dying dual relay. If there has ever been a spike in the system the 10 gauge brown wire coming directly from the battery could burn it out or make the contacts iffy.
A sticky flap in the AFM.
An air leak somewhere along the rubber intake boot.
A poor connection on the back of the ECU.
And grounds of course. Primarily the two on the intake plenum, which are for the injectors.
Ron

[emosfiat]

Thanks Guys. I did have an electrical melt down the other day. Had to rewire a bunch of connections. Looked at the ignition switch. Looked ok but did not take apart. I will try this next to be sure no bad connections. I will keep in touch.

Emo

[zachmac]

Also don't overlook the temp. sensor on the T connection coming out of the head. If that connection is frayed / loose / failing it will give you all kinds of fits from no running to running like crap. I was wroking one day and bumped mine and all of a sudden it ran like crap. Sure enough the connector wiring was loose / frayed. New connector there and it runs like a champ!

A propoerly sorted FI system is indeed a joy. A malfunctioning one is a PITA. However, that said I would go with the fix it versus swap it out crowd. In the end you end up with a hassle free system. BUT, if you are going to want to modify your car much in the way of performance I would say swap to the carb as the Bosch FI is basically non-tunable.

[mbouse]

well, if you are gonna talk about frayed wires and such, don't forget that there are a lotta wires that would cause your intermittant issues that are not related to the F.I. system, and would/are common to the carb'd systems. starting with a frayed magnetic pickup lead... these fail so often that many of us carry a spare.

[dsnyder]

Many year ago I had a 1975 Super Beetle that had fuel injection. I was talked into removing the fuel injection and putting on Dual Webers. It ran and met the basics but it was never as fast and never got the fuel efficiency the car did with the fuel injection. I always had emission issues and I learned alot about tuning carbs... constantly. I regretted the change all the time.

[SpiderJim]

I picked up a second Fi spider that had been stored for 10 years and went over everything to get it ready for a long trip North. I had it running quite smooth but had only clocked about 20 miles before my trip. Everything seemed good until it also started to do strange random things. Stutter one minute then fine for a while along with the odd misfire and so forth then run okay. Went through the entire systems without much luck. Finally got it home with the last 50 miles or so getting worse. I had already changed out mag wires and all the ignition bits along with fuel pump gas tank/injector cleaning and so forth. Turned out to be the AFM sensor flap slightly sticking or not based on outside temperature and moisture due to the closeness of the gap.

On further examination I also found two wear spots on the resistor plate inside the AFM itself. These spots are at idle and low MPH range and then at around 65 MPH cruise. One would expect this wear to be the most in these areas. Under test these areas gave out intermittent Volt levels and not smooth as it should be. I filed and sanded the flap to get it smooth but still had a little stumble trouble but also much improvement. So rather than flog a dead horse I was able to purchase an entire FI system off both ebay and the local craigs list that had all the Fi parts from fuel rails with injectors to the AFM and plastic pipe. Got them both for around $75 each complete with all the sensors. My car had >75K miles and the doner less than 40K. I would suggest that you might try this approach as it is cheap way to test and you would also have backup parts worse case. After reading up on Fi systems and being and elec engineer it just all seemed to make sense. Car is fine now. However, what the other guys suggest is of great value and should be checked out. One other thing. After changing the AFM out and the other stuff when putting it back together I found a large crack in the plastic plenum at the AAR attachment pipe that was invisible until attaching the rubber hose and putting pressure on it ... only luck made me find this and it was sure nice to have two more in stock to exchange immediately.