D-jet expert needed

[nah325i]

Hey guys - I need some D-Jet help if there is anyone around who still remembers that system... I'm actually working on my Mercedes but, well, we all know that I'm not going to find much help from the other Benz guys. The system is basically the same as a 914 - I've been methodically sorting through lots of issues. It still runs like crap. When I first started digging into it I found that the fuel return was blocked and it was running 90psi in the rail, obviously running rich. It also had massive intake leaks which were counteracting the extra fuel and it was actually running pretty decent, albeit very rich. Long story short - I've fixed the fuel pressure and vacuum leak issues. Its running lean - it runs OK if I bump fuel pressure to about 60-70psi by crimping the return line. I've been through the tests on all sensors, adjusted tps, all new ignition components and checked timing. Pulled/ cleaned / tested injector trigger points. Could running at 3 times the standard fuel pressure have damaged the injectors? My gut tells me yes but I want to hear it from someone else before dropping 700 bucks on a new set. I have confirmed that they are all firing (by listening with a stethoscope, I don't really have a way to bench test them). Any other thoughts? I've swapped ECU's as well and its runs about the same... Will not even idle at 30-40 PSI in the rail unless I disconnect temp sensor 1 which should make it richer... Thanks for any help.

[BeeMaster]

My dad says you probably didn't damage your injectors, in happened to him once in his
T3. He wants to know the resistance at the temperature sensor at a given temperature
So check resistance and know what temperature it is at and come back with those 2
Numbers and I will give them to him and see what he says. Good luck.

[Dave at Pelican Parts]

I find it difficult to picture any sort of damage that could be caused by high pressure which does not allow as much fuel through the injector. I also know of more than one person who has blocked the return line in their D-jet system without permanent damage.

You can bench test the injectors relatively easily. Presumably they are accessible? It is probably just one M6 (10mm wrench) nut that holds them in; the electrical and fuel connections should stay connected to the injector pretty easily. Stick the injectors into some glass jars and watch them while someone cranks the starter. You can check that the fuel quantity roughly matches, and watch for the spray pattern that way.

Disable the spark while you're doing this, just for safety.

Odd thought: Is your fuel pressure gauge correct? I had one that read significantly high, and when I set the pressure according to it my car would just barely run. Fortunately my mechanic double-checked it with his own gauge and found the problem.

Have you read through the Brad Anders D-jet website yet? Brad's '70 914 2.0L

--DD

[nah325i]

TS1 (coolant) 1.541 k Ohm at 77F
TS2 (ambient) .372 k ohm at 59F

On another note I pulled a bank of injectors and observed the flow while cranking the engine over. They were shooting streams, not the nice cone of mist I'm used to seeing (however I've never looked at d-jet injector spray patterns before)...

[nah325i]

Hey Dave,
Thanks for the reply - I've read through Brad's site, it was very helpful in testing the rest of the components... As for the pressure gauge, I believe it to be accurate because when I fixed the blocked return line and installed a new pressure regulator the gauge was reading 30psi which is exactly what it should show. The spray pattern I observed does not look correct to me, I'm going to pop one new injector in and compare it to the others before I replace all 8... I'll report back. Any other insights?

[nah325i]

injectors fixed it!

[BeeMaster]

He says ts1 and ts2 look good. Injectors you should be able to hit the car 3 stalls down
They don't mist they are like a fire hose. He says check for oil on the pick up points of the distributor.

[nah325i]

I saw a big difference between the spray pattern of the old and new injectors so I went ahead and changed them all. Car fired right up and is running pretty well for the first time.

[BeeMaster]

Good glad you figured it out. Have fun.

[Dave at Pelican Parts]

Excellent! That was probably an underlying problem all along, and was being masked by the fuel pressure problem.

You can send the old injectors out to somewhere like Witchhunter Performance for a clean and test. At least you'll have some good spares at that point, right?

--DD