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914World.com _ 914World Garage _ Need L Jetronic FI help..1974 1.8

Posted by: jasoncm Nov 2 2011, 05:21 PM

1974 1.8l that I have had for 5 years. Has always started right up and ran strong all the way to redline. Had a fender bender, and took it to body shop. Due to limited parts, it took 6 months! So I go to pick it up and the guy says "yeah....its not running so great." He says that he did not touch the engine bay, but I have no idea how it was treated or stored. (we had a heat wave in Dallas).

So now here is what happens: Starts easily with a flick of the key and idles fine. If you press on gas pedal the rpms will struggle up to 3000 and then, instantly it loses power and falls back down to idle or dies. No matter how much you feather the throttle, it always struggles to 3000 and then loses power. Still starts and idles fine, but not enough power to move.

My thought was that maybe the body shop idiot was flooring the gas when he started and it backfired and damaged by air flow meter flap. I checked the flap and its movement seems fine.

Any ideas? Again, the car ran great when I left it, now it has these symptoms. Fuel pressure regulator?

Finally, does anyone know what pins on the Air flow meter I check for resistance?
Any help is great! Jason

Posted by: Jeff Bowlsby Nov 2 2011, 06:25 PM

I have a couple good L-jet manuals here for the pin-out testing:

http://bowlsby.net/914/Classic/TechNotebook.htm

Posted by: messix Nov 2 2011, 06:38 PM

shop rag stuffed in the intake horn?

Posted by: RRietman Nov 2 2011, 07:27 PM

six months in a body shop? bad gas now? fuel filter? air filter? (not likely). I like the bad gas idea. the shit we get now lasts about 4-6 weeks and starts to sour.
Randy

Posted by: zonedoubt Nov 2 2011, 08:27 PM

Run through this: http://manuals.type4.org/ljet/

Posted by: Valy Nov 2 2011, 09:04 PM

Looks like fuel delivery problem to me.
I would check the fuel pump. Probably it doesn't have enough flow to handle the fuel demand under acceleration.

From what you describe, the AFM should be OK or else the engine would not rev-up. The ECU disregards the AFM reading at idle and WOT so the symptom you describe should not be related to the AFM.

To test the fuel delivery use this:
http://www.harborfreight.com/fuel-injection-pump-tester-92699.html

Posted by: jasoncm Nov 2 2011, 09:33 PM

Thanks for the responses:
1. Valy, I agree it seems like a fuel issue..b/c nothing was changed on ignition side. As you mention, the AFM has an idle air bypass, so my thought is even if the AFM was bad it would still start and idle fine--which is what it is doing. The fact that it drops back to idle at precisely 3000 rpm leads me to believe maybe the potentiometer in the AFM may be damaged or corroded. Would a bad fuel pressure valve cause this? Why would that go bad just sitting there?
2. Bowlby, thanks for the manual references. I'm aware of the ohm readings to test across pins 6&7 and 9&8, I'm just not sure which pins those are! I need a pin diagram. I will search some of the other manuals you referenced to see if I can find it. Good resource!
3. Randy, I thought about the bad gas thing, but I would think that would make it run rough or poorly--not stall out at precisely 3000 rpm every time. Gonna change the gas anyway. I hope its that easy!
4. Zonedoubt, thanks for the link. That is actually a modernized outline version of the old Bosch L-jet flowchart. Went through that thing 10 times!
5. Messix.....I wish it was just a shop rag in the intake!

thanks again for the responses....hope to work on things this weekend. And yes, don't have a fender bender that requires a new front bumper...it takes months to find a good one!
Jason

Posted by: kg6dxn Nov 2 2011, 09:52 PM

Another L Jet Manual

https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0Bzy-cXUDftdrOTg3OGQzM2ItZmJmMi00YmIyLTg2MDctNjFmYTU2MTdiNDMx&hl=en_US

Posted by: Valy Nov 2 2011, 10:48 PM

QUOTE(jasoncm @ Nov 2 2011, 08:33 PM)

1. Valy, I agree it seems like a fuel issue..b/c nothing was changed on ignition side. As you mention, the AFM has an idle air bypass, so my thought is even if the AFM was bad it would still start and idle fine--which is what it is doing. The fact that it drops back to idle at precisely 3000 rpm leads me to believe maybe the potentiometer in the AFM may be damaged or corroded. Would a bad fuel pressure valve cause this? Why would that go bad just sitting there?

There is a throttle position switch that indicates Idle/midrange/WOT. The ECU uses the AFR in the mid-range and has fixed settings for Idle and WOT.

I think the fuel pump is the trouble maker and not the regulator. You just run out of juice at 3000 RPM.
Try this: accelerate slowly and it will probably die at lower RPM and probably cough before dying. Floor the pedal and it will rev higher before suddenly dying.

Posted by: Drums66 Nov 3 2011, 07:28 PM

.....RESISTOR PACK WIRING?
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