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Posted by: Levi May 6 2004, 02:26 AM

My 74 1.8 L-Jet is giving me trouble, At start up, engine cold, it will idle rough (400-500 rpm) and seems to be loading up?, after 3 or 4 minutes the rough idle goes away and it will idle at 900 rpm's, but if I ease into the throttle it cuts out around 2800-3500 rpms, but I can rev it to red line. after driving it 2 or 3 miles it seems to clean out and runs great, however it will from time to time die when I have the clutch in while stopping.

Where should I start looking

Posted by: Mark Henry May 6 2004, 07:55 AM

L-jet is very sensitive to vacuum leaks. First check all of the hoses, look for cracks in the hose and the rubber elbow. If they are old it's best to replace them.

Also check the oil cap, there are two rubber seals and they must be in place, see pic


Attached image(s)

Posted by: trekkor May 6 2004, 08:06 AM

Possible cold start injector leaking or bad head temp sensor.

Inspect all the vac hoses first, of course.

L-jet is a closed vac system. Check that the seal on the oil fill and gas caps are good, too.

It's not too much work to replace all the gaskets, seals and suspect hoses. I did this years ago. This is also a good way to learn about your system, if nothing else. Set aside a weekend. Don't start until all parts are in hand.

Do a full tune-up as needed.


It's nice to get a fresh footing, know where you stand. Esp if you are not the orig owner.

Posted by: Joe.D May 6 2004, 08:08 AM

Pages from the Bosch troubleshooting manual can be found here


http://persweb.direct.ca/aschwenk/TroubleshootingtheLJetronicSystem.htm

Posted by: jim912928 May 6 2004, 08:10 AM

Ditto what everybody has said. My 75 1.8 with L-jet wouldn't run for anything. Replaced all fuel lines starting at the tank, fuel filters and every vacuum line and it runs like a top. Dont forget the fuel injector seals also (easy to change).

There is a good diagram of all the vacuum lines and fuel lines with lengths and diameters on the pelican tech site. I followed them to the letter and actually found that the previous owners had vacuum lines hooked up wrong.

Once you get the system leak free..it runs soooooooo smooth!

Jim

Posted by: Dave_Darling May 6 2004, 09:43 AM

You start just the same way you do if you have D-jet, or carbs.

Verify that the ignition system is in good working order. Make sure all the adjustments are correct, the parts are good and working nicely, and so on. Make sure that the "basic engine" is in good shape, that the valves are adjusted correctly and that the motor has decent compression. Make sure that all the wires and hoses are hooked up correctly, cleanly, solidly, and that none are brittle or cracking. Verify that the fuel pressure is correct for your type of system. (Haynes has the info for the L-jet, I forget the exact number.)

Then you check through all of the intake system for vacuum leaks. The rubber "boot" from the air flow meter to the throttle body likes to crack in between its accordion pleats, where it's hardest to see of course! The oil filler can leak air as well. So can the throttle body. So can other parts... Pretty much anything between the air flow meter and the cylinder head is a possible source of leaks!

Then you can move on to checking the actual FI parts. Haynes, surprisingly, has pretty good info on all of those! They're not quite all together, but they are in the Fuel System chapter and the tests are good as far as I can tell.

--DD

Posted by: Levi May 6 2004, 10:24 AM

Thanks for the ideas so far guys,

Its all tuned, do you guys really think it could be a vacuum leak, I ask that because once its at running temp. it runs like a top, its smooth thru the rpm range and pulls hard.

I will start checking/replacing the hoses tho, they are braided and look like they might still be original.

Posted by: d7n7master May 6 2004, 01:08 PM

If your really having trouble shooting L-Jet your either not using a big enough gun or your sights are off.

Posted by: Joe.D May 6 2004, 06:28 PM

If it runs well after it warms up, focus on the cold run components. My first suspect would be the Aux Air Control. Check to see that its open when cold. If its stuck closed, cold idle would be very low, since the engine isn't getting the extra air added to the richer warm up mixture.

It isn't easy to check without removing it, but with a small light and one of those dentist mirrors, you can manage to look into/through it. Its located just behind the oil fill tower. Sorry, can't post a picture of it right now.

Joe

Posted by: Levi May 7 2004, 02:02 PM

I'm missing the middle seal on the oil cap...where can I get a replacement..

Posted by: Mark Henry May 7 2004, 02:28 PM

Pelican, HPH, etc. or even the dealer (Porsche or VW) can get it for you.

Posted by: Levi May 7 2004, 04:28 PM

Tanks Mark..