More CIS Injector Flow Questions - Video of Spray Pattern
 

Ok, tonight I video'd the injectors spraying. It seems that I have a good cone shape spray at full volume but at low volume, the injectors sputter. Just wondering from the experts if this is normal.

I ordered new injectors which will be here tomorrow and I'll have to compare.

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One of the problems reported with cis is irregular injector spraying if the fuel lines are changed to a less rigid type, thinner wall line. I have read a few threads where the fuel ines flex from the high pressure and this causes a pusling of the injector. It is very important to have the correct type.

Mine don't spray like that at all. On either 74 I've had.

+1 on what Ed said.

I will have new injectors tonight and we will see if there is any change. Is there any other possibilities besides fuel lines - I have new Coline Fuel Lines and they are the correct lines. They might not look like it in the video but that is because of the protective covers on them.

Hmmm.... How do the o-rings look on your PRV (pressure regulating valve), for want of a better word, on the right side of FD behind air box?

Edit: Does the PRV move freely? You might have to stick a wooden dowel or the like in there to remove it. There are some shims and a spring(not very stiff) so don't lose anything.

I can't see the video. (work blocks Youtube) so this is without seeing it.

What are your pressures like? Do all your injectors do it or just the one?

Couple things could cause pulsing.

I would think sending them out for cleaning would probably get you virtually the same result as new injectors and save you money too. I sent mine to Mr. Injector and it cost less then $110 with shipping. My car ran noticeably better than before, especially at lower RPM.

I think (and I'm hoping) that you hit the nail on the head. I've tested my fuel pressures within the past two months and they were in spec. I recently removed the fuel distributor, to paint and replace the o-ring underneath but I didn't touch anything with the pressure regulator. The car has had an annoying jerk when running at low idle and this has been going on for several months but seems to be getting worse. I replaced all of my vacuum lines, O-rings, crush washers, injector seals, etc.. in an attempt to fix.


It was definitely more expensive to buy new ($283 for the set), but they are sitting on my front porch as we speak. This gives me peace of mind and I will sell the old injectors, for cheap, to someone who needs them.

During your pressure tests... did you have a lot of needle fluctuation?

I don't recall that to be the case. It's been a while but I remember the fuel pump pressure to be consistant and right on spec. I did have warm pressure issues but I have replaced the WUR with a good unit since then. I'm going to retake all the pressure readings this week.

Based on the FD output pulsing at very low volume, I am inclined to think it is the pressure compensation component.

I have posted another post which questions the mixing of CIS components. I was asking this because the former owner (a very accomplished Porsche Mechanic) had modified my CIS to include a '74s 2.7 engine, '76 WUR, and a '79 Fuel Distributor. I was thinking that my fuel distributor could have issues but maybe it's just the pressure compensating spring/o-ring. I don't think the '74 FD has this component.

Here's the link to my other post which has a complete spec sheet of what the prior owner did when he rebuilt the engine.

http://forums.pelicanparts.com/porsche-911-technical-forum/778927-question-mixing-cis-parts-different-years.html

I installed my new injectors last night. The spray pattern improved but the low end sputtering continued, albeit a little bit more uniform.

The car is running much better and is smooth as a top at cruise. It's still idling a little bit rough and still has some light backfiring in the exhaust when downshifting. However, this morning's 30 mile drive to work was a pleasure and no comparison to the bucking and jerking that's been going on over the past week.

I ordered the pressure regulator kit for the Fuel Distributor and I'll see if that helps. It should be here by Thursday.

Lastly, I'm going to re-measure my fuel pressures this weekend and check/adjust the mixture settings. I have a quirky exhaust gas analyzer but it works (can't remember the brand but it's not a Gunter).

Thanks for all the advice!

I hope it has nothing to do with ignition.

Do you have a Pertonix installed in the distributor?

Any progress?