DJet idle issues

[DarrenG]

Hi,

Still working on the ebay special. 74 2.0 with D Jet. engine completely rebuilt, not easy to start, but can be done. I can get it up to 4000 rpm's, but only if I constantly feather the gas pedal. If I let off, it dies.

checked the fuel pressure today and it holds at 30.

any suggestions? could this be timing?

Thanks

[Tobra]

timing or vacuum problem most likely. How are your vacuum hoses?

[R_Davis]

I had the similar issues with my 72 1.7. My problem was that after replacing all the hoses and vacuum lines, I had a couple of vacuum hoses in the wrong places.

Have you found the correct timing marks on the impeller? You're gonna need a mirror and a light to find them. There is a great tech article here on PParts. The

I suggest you go to this site, print this manual on the D-Jetronic layout and keep it forever. This is invaluable. http://www.icbm.org/erkson/ttt/engine/fuel_injection/d-jet.html

Also, these engines were meant to use 98 Octane. Add a bottle of Lucas Octane Booster to the tank.

Triple check your timing, dwell, hoses, lines and fuel.

[Dave at Pelican Parts]

Good advice, except for one point:

Originally Posted by R_Davis

Also, these engines were meant to use 98 Octane.

No, they weren't--at least, not if you're looking at the octane numbers on the fuel pumps in the US.

The 2.0 was spec'ed to use 91 RON, which is equivalent to ~87 US pump octane. The early 1.7s were spec'ed for 98 RON and 86 MON, if you average those to get the US pump octane rating, you get 92 octane. And 1.7s have historically ran fine with the 91 octane fuel that passes for "premium" in California.

--DD

[RandyLok]

Most Djet vacuum leaks create high idle issues. In your case, check the one to the MPS. If that one is unplugged it will run full-rich and create problems like you describe. Otherwise a vacuum hose is not likely just yet.

Timing.... If it is WAY retarded, maybe. Dwell for sure - if the point gap is too close you could have these symptoms. If you don't know the dwell and timing are correct, then you need to set that as a baseline. Trying to tune an engine that has the timing or valve adjustments off is a waste of time.

Listen to Dave. These engines were NOT meant to use 98 octane fuel. Octane is not the same as RON. They run fine on regular!!! If you have a high compression engine and you're getting pinging, then you may have an exception. Otherwise don't waste your money on premium fuel or octane additives.

Yes, DO check your dwell and timing. Check the vacuum line to the MPS. Check your valve adjustments. Do those things first and report back.

Then maybe look at fuel delivery... Filter, pressure.

Keep us informed. This is good stuff.

[R_Davis]

Hey Darren, Dave and Randy ...

Thanks for the clarification on the octane rating. My info was based on pg. 78 of the 1972 PORSCHE 914 owners manual ... it reads ...

Fuel tank 16.4 US gals (62 liters) including approx 1.6 US gals (6 liters) reserve
Required octane rating: 98 octane (premium fuel)

Dave ... what does ... 98 RON and 86 MON ... mean exactly?

Darren ... Always defer to Dave. He's the man!

I will admit; however, that I didn't get my engine to blow out all the crap in the system until I added a $4 bottle of Lucas to my tank and took it out on the open road. I still use half a bottle in every tankful just as a preventative thing. It also is a wonderful hair conditioner for my lucky rabbits foot

[RandyLok]

GOOGLE is good for this kind of stuff.

[Dave at Pelican Parts]

RON is the Research Octane Number. (ROZ is the German abbreviation for the same thing.)
MON is the Motor Octane Number. It's a somewhat different test.
US pumps measure in AKI (Anti-Knock Index), or simply "(R+M)/2". Which is the average of RON and MON.

For a given batch of fuel, the MON is typically 8-10 points lower than the RON rating of that same fuel.

Therefore, the US pump octane rating will be 4-5 points lower than what is typically listed in the manuals of older European cars, most of which call for a RON rating for the fuel.

--DD