rdhayward

I didn't want to hijack the thread about superchargers with an off-topic post about fuel injectors, but Carl brought up an interesting subject when he noted that new 'gen 3' injectors boosted the performance of his supercharger setup.

This has led me to do some homework on injectors. I found several YouTube videos that are relevant, particularly from this guy (he has other videos comparing old vs. new Bosch injectors side-by-side):

http://www.youtube.com/watch?v=VfynoxL2RZI

So, anybody have a Bosch part number for 968-compatible Bosch Design 3 injectors? From what I can find online, the stock injectors flow 28 lb/hr (296 cc/min) and have impedence of 15.2 ohms.

odurandina

Great job posting, I was thinking exactly the same... I just didn't think it would be appropriate to nag Carl about that after such a triumph.

I figured just an extra pay-check.

Jfrahm

Likewise. By the way the old injectors fire at about 0:55 into the video and the new ones at about 3:00.

rdhayward

I sent the maker of that video a PM via my YouTube user account:

Sir, I shared your video with several Porsche-lovers - we all own 968 models that were made from 1992-1995. These had Motronic setups and came stock with Bosch 0 280 155 010 injectors. What would be the most ideal Design 3 replacement injectors?
Thanks,
Ralph Hayward
Austin, TX

He responded this morning:

hi here is the replacement they are in sets of 8 but a good deal
http://fuelinjectorconnection.com/sh...od&productId=5
jon

kwikt

Wow, wonder if anyone tried these!

mattipuh

interesting topic. with common sense it could be that more fine spread fuel would burn better, but would really to be compared to what 2nd gen injectors can do. Is there any value for injectors, what kind of mist do they provide?

John Etnier

Anyone want to split a set, feel free to get in touch. I'm at the very least interested.

phil0618

I have some interest, but can anyone familiar with the process of changing injectors enlighten me as to what all is involved? Is there a link here or at Clark's garage or somewhere that talks to this.

I'm leaning toward one of Carl's supercharger setups in the spring so if this is a likely prerequisite to get the most out of that setup it might be worth getting it done now. Does anyone know if these are in fact the same injectors that Carl used?

Splitting a set of 8 with someone is certainly an attractive proposition if the wrenching isn't too intense.

Phil

jpk

The injectors he listed are high impedence, we need low impedence (15 ohms or so) to keep the DME happy.

John Etnier

Changing injectors is very easy AFAIK: DIY anywhere here?

jpk

Changing fuel injectors is only marginally more difficult that replacing spark plugs. Clark's has a general 944 DIY; not much different for the 968 except you need to remove the cover for the fuel rail.

User 41221

Since I am getting ready to pull mine for cleaning, I should really take some pics and post the DIY, but yes, its very easy.

The basics are (done from memory after two Sailor Jerry cokes, so cut me some slack):

1) Start the car and then pull the fuel pump fuse. The car will die and it will depressurize the fuel system some so you don't shoot fuel all over the place when you pull the first injector off (or ideally, pull the cap off the rail) to drain the rest of the fuel out of the rail.

2) Pull the ground off the battery. Saftey precaution only, but sparks and gas are a bad mix.

3) Using a 4mm allen head socket/wrench, pull the four bolts that hold the cover over the injector. On the intake side, be sure to catch the spacers, seems like I drop one *every* time I do this. lol Also, on the valve cover side, the rubber absorber mounts are rather frail, so wrench carefully or plan ahead and get two new ones.

4) Pop the black plastic cover off the fuel rail. Be careful not to break the tabs off. Push it off toward the valve cover to start removing it and then look for the tabs on the back side. And don't feel bad if you break one, I did and I've done this before.

5) Optional: Undo the fuel lines at the back of the rail/fpr using 17mm and 19mm wrenches. Its not necessary but it does make it a bit easier to pull the rail up and ensures that the fuel system is completely depressurized. If you are completely pulling the rail, also disconnect the vac line on the fpr. You'll also have to clip the black nylon tie wraps to separate the injector and variocam harnesses from the rail if you want to completely remove the rail from the engine compartment.

6) Disconnect the injector wiring harness from the four injectors. Um, if I have to explain how this is done, you probably shouldn't be attempting this, but to be thorough, push in (and hold) on the wire retaining clips and then pull the connector off.

7) Remove the four 10mm bolts that hold the fuel rail down.

8) Pull the fuel rail straight up firmly, and it should come free.

9) Pop off the retaining clips from the injectors at the rail. Injectors are then free and a slight tug down from the fuel rail should free them. Make sure the o-ring comes off with the injector or else fish it out of the seat on the fuel rail.

10) Installation, as they say, is reverse of removal. Coat the injector seals/caps with ATF fluid so that they have a lubricant on them when you reinsert them.

Helpful hint... don't go crazy retightening the bolts that hold on the fuel rail, they strip easily enough. Fuel rail bolts should be torqued to 8 ft-lbs.

MANDATORY: After servicing your fuel system, start the car before you put the cover back on and inspect for fuel leaks! Any sign of a leak, turn the car off immediately and figure out whats causing it.

That should be close enough to get anyone through it. If you feel uncertain about doing this, get help from some one (there's plenty of Rennlisters around, reach out and ask for help. Its usually more fun to work on cars with friends anyway!), or take it to a shop. Much better safe than sorry when it comes to fuel. ALso, I am NOT responsible if you follow my directions and still manage to burn your car and house down, okay?

Don't use the wrong impedence injectors on your car. Your DME won't like it. [Edit: corrected as per rdhayward comments. I stand corrected]

Regards,

rdhayward

OEM 968 injectors are "high impedance," rated at 15.2 ohms.

Low-impedance injectors are 3-ohm range, even less. I think the fellow who tried S2 injectors found that using low-impedance injectors (2.2 ohm) in a 968 encountered some difficulty.

FRporscheman

Interesting topic.

How are these fancy gen-4 bosch injectors different than Siemens, Delphi, etc?

savvas944

so the theory of std injectors maxing out at 295 bhp seems correct ,whatever you do.and need bigger injectors with more fuel flow to go over 300.i.e. from 28 lb to 32 lb
anyone has the Bosch part number for these new injectors and what is their impedence?