Looking to replace my fuel injectors and just wondering what my options are. The car is an 82 US 928 w/auto. I,ve been dealing with some rough running issues and I had the injectors sent out for cleaning. When they came back the paperwork stated that some were in poor shape and the rest in fair shape,so it may be to my advantage to just replace them. Whats out there as far as good options? New,used,refurbed?

 

If it were me, I would consider getting adapters from Greg Brown of Precision Motorwerks so that you can fit a modern 4-hole injector. Judging by your avatar, the car in mention is a US-spec. As such, you can use high or low impedance injectors.

 

^^ as stated above you can use high or low impedance injectors. I did this to a 944 and have never had any issues with it as they use a similar computer.

Just make sure you use something in the range of 21-24 lb/hr or their cc equivalents. Any less and it will run lean, any more and it will run rich. The NB 02 sensor can only account for so much.

 

Hi Chuck,
This topic has been the subject of much debate. I suggest you do thorough research before changing to any nonstock configuration. Listen to our experts carefully. I went through the same thought process with my US ‘83 - the idea of using the GB adaptors with 4-hole modern (and cheap, but high impedance) injectors does seem alluring - but read the following thread carefully. It didn’t take much research for me to decide to stick with stock. You can search and find a number of other threads too. And btw, the GB adaptors were not intended for your application, as noted by GB in this thread.

https://rennlist.com/forums/928-foru...dance-car.html

Also, I posted my Witchunter results at post 29 in the following thread. If it were me, I’d spring for new (correct) injectors, they are still available. Pricey perhaps, but still available. Or source good used ones. You may not need to replace all 8, correct? How much variance do you have? If you just need to replace one or two this is a no-brainer.

https://rennlist.com/forums/928-foru...oses-83-a.html

Be sure to replace all rubber seals and all flexible underhood fuel hoses if that’s never been done - also documented above. Use DC 111 Molykote on all the rubber seals and use anti-seize on the fuel line junctions, only the threads, and torque only to recommended settings so that they can all come apart manageably next time. Re-use the hats on the injector-to-fuel rail tubes. Roger sells a great kit containing all the injector seals and connecting tubes, and stocks all needed fuel lines.

Good luck!
Rick

 

Literally, from Greg's site, the adapters are advertised for MY80-84 US & MY84-86 Euro.

 

Hi Kiln,
I'm glad you mentioned that -- I had forgotten about that. I got all excited too when I read that on GB's website. I spent a LOT of time poring over every single bit of information I could find on topic, both on Rennlist and elsewhere. After doing the research, I asked Roger -- who stocks these adaptors -- about exactly which injector is recommended to go with them for a stock L-jet application. There isn't one, and I was advised to stick with stock. Of course, I encourage you, the OP, and anyone else to spend the time, do the reading, pick up the phone and do your OWN research.

Soapbox time: Having said that, this does bring up the perennial learning/teaching point: Just because you CAN make a "change" on your car, does that make it "better"? Just because somebody says X on the Internet, or parts are offered for sale, does that mean they will work as well as stock? What if there's even more evidence, and some people report that things "work" -- does that mean that they have put in the hundreds or thousands of hours of testing, across a large variety of cars and conditions, and put in anything even approaching the testing the factory did, to ensure that it "works"? It's one thing if we are talking about a gasket or a fuel line, but an entirely different thing when we are talking about the heart of the fueling system. What are the potential consequences of getting that wrong? Are you willing to roll those dice? Are you willing to roll those dice and make that armchair quarterback recommendation to someone else who has to run those risks? What if THEY destroy their L-jet controller or even blow up their engine following your advice?

The only reasonable approach to take here, as in virtually every case about aftermarket or nonstock parts, is to come in with a very strong presumption that the factory parts are best unless proven otherwise by clear and convincing evidence. Sometimes that standard can be met. In this case, that standard is not even close to being met -- in fact there is very little evidence at all in favor, and much expert advice against. It's up to each individual owner to take the time and effort to do their own research and come to their own conclusions. Some people will WANT to experiment and be a guinea pig, and that's perfectly fine as long as it is an informed decision (and not fine if they think it's perfectly safe and not an experiment). But frankly, without this presumptive approach, it's all too easy to mess up our exotic cars -- remember, these were some of the most expensive cars on the market in their day, and the top of the Porsche line -- because of the law of unintended consequences.

End of soapbox.

 

rtjw,

I don't think you have said anything that I can't agree with. I see your perspective and don't discourage anyone from making their own informed opinion with regard to part options. Just because there are options doesn't mean that an improvement is available over original equipment. That said, I see GB's upgrade as a no-brainer. It's economical, increases serviceability, and works. Are you concerned about low impedance drivers versus high impedance injectors?

 

Hi Kiln! The thread I linked says it all, there are some subtleties with the drivers in the L-Jet controller which raise the question of not whether, but how well and for how long a high impedance injector would work. Also, there are not a lot of opinions I trust on this site or anywhere on the Internet, but some of those I do trust, highly and as trusted experts, do not weigh in favor of this modification (with zero trusted experts in favor of this modification). My conclusion is that using a high impedance injector is still firmly in the realm of experimentation and is therefore attached to an unknown and potentially significant risk level. Until and unless there is a significant amount of tested and proven long term success, testing and monitoring A/F ratios and some way to demonstrate lack of long term harm to the controller, over a significant community, over significant time, and over a significant variety of conditions, my own personal conclusion is that it is not a proven quantity and therefore not something I would use, or recommend, as being a drop-in replacement for stock. But with enough solid scientific and tested evidence, I'd switch my opinion, we're just not there at this point in time that I am aware of. That does not meet the standard of clear and convincing evidence to overcome the presumption that stock is best. As is so often the case, we should not follow any path of making an ill-informed decision to use of non-stock parts JUST because it's cheaper than stock, nor fall for the illusory promise of an aftermarket part being "better" without clear and convincing evidence that proves it. FAR too many 928s have become junk or damaged by the use of substandard and/or nonoriginal parts already. To the OP: Do the research -- Weigh the costs and benefits -- Question and evaluate the evidence -- Maintain the presumption and evidentiary standard -- Come to your own conclusion. Spend the bucks needed to do what is best for the car. See post #4 above. Good discussion!

 

The L-jet controller is a true 'peak and hold' ECU whereby the injectors see separate current signals. The low impedance injectors require more current to open. Since the high current is only needed to open the injectors, the L-jet switches the injector command across a higher resistance path to 'hold' them open as the increased current isn't needed. Less heat means longer part life.

High impedance injectors are originally intended with 'saturation' drivers, or a single current signal. The injector itself is a critical component for this type of signal, as the 12V power signal is constant. The lower current circuitry is achieved via the increased injector coil's resistance. In other words, driver current is dependent on the injector in this application. High and low impedance is really pretty generic language. Using 12 ohm (high impedance) injectors versus 16 ohm (high impedance) injectors means more current on its driver. How do we determine this is okay?

A high impedance injector driven by an L-jet controller will open in the same manner it was intended, then be switched to stay open at 'hold' current that isn't needed with this injector type. It's this side of the L-jet command that should be our point of interest in determining retrofit injector compatibility. Will the injector stay open for the whole pulse width? The 'hold' current will be between 200-250mA, depending on the 'high impedance' injector chosen. The driver current on a Euro S2 is a 'saturated' 750-830mA for comparison. The L-jet 'hold' current can easily be simulated, and a proper bench test with a 947 blue top injector can be executed.

The Lucas - D1540BA injector would be the most ideal replacement for MY80-84 US cars with the GB adapters IMO. These are peak and hold injectors with the same plug and body as the 947 injector from all that I can tell. The caveat is that these aren't 4-hole injectors, though they're a lot easier to find than 0280150154 injectors.

 

Excellent discussion gentlemen! 2 opposing thoughts and opinions expressed without bickering or name calling!( something too common on other forums I visit). The information and opinions brought forth will give me something to ponder before I jump either way. I can definitely understand going with the "tried and true" and also going with the new and possibly "improved". Time to study both. I,m in no hurry as the nice weather is definitely changing and the 928 will be in the garage and off the road for the winter. Thanks again for the information and time spent expressing your thoughts, i do appreciate it!
Chuck

 

I spent a little time with the 928 this afternoon replacing spark plug wires. Still suspecting a few injectors causing a rough running issue but checking other possible culprits. I did pull injector plugs 1 at a time while idling and discovered when pulling the plugs on cylinders 7 and 8 there is no change in the engine....pulling any of the other 6 will cause the engine to bog as you would expect. Noid light confirms all are getting signal. so, I have new plugs,wires,cap,rotor, injectors sent for cleaning but came back in good but not excellent shape. I checked compression a while back and all cylinders were decent and all in the same range. also have a new fuel pump, and regulators. is there something else to check or is it safe to point a finger at the 2 injectors and go ahead and replace them?
Chuck

 

Hey Chuck,
I’m sure others with much more knowledge will chime in, but it’s good you appear to have injector pulses on 7 and 8. Have you confirmed whether you have spark on those two cylinders? And what do those two plugs look like compared to the others? Have you tried confirming visual
spark?

Btw the L-jet system grounds out pairs of injectors via a common pin, but 7 and 8 are not grounded together, so FWIW that probably means not a controller type of issue (good news). More here post 3: https://rennlist.com/forums/928-foru...tml#post285204

Besides spark, another potential issue is the individual connectors on 7 and 8, is it possible that wires are cut or frayed? Also the little pin fingers (on the harness side) can sometimes be bent or distorted and not make proper contact. Corrosion on the pins is also a constant issue, have you made sure all injector and harness pins are nice and clean? How about the big connector at the Ljet controller, the connector at the central board that supplies power (on my ‘83 it’s connector X), and the two grounds on the passenger cam tower? Frankly a power/ground issue wouldn’t seem to fit your symptoms, but while you’re in there, you should tidy everything up. Get some deoxit and use liberally, and you can find threads sharing advice on cleaning brass connectors etc. Thinking out loud here...

As for the injectors themselves, you say they’re only ok. How much variance did you have and did you track which injectors you installed in which cylinder? What were the numbers on 7 and 8? Did the injector cleaning service do a pulsed flow test, which would presumably confirm the injectors were actually operational? Bottom line, if you suspect injectors on 7 and 8, that should have been apparent in the test data. If 7 and 8 tested similarly to all the others (and presumably they did or you wouldn’t have gone to the bother of putting them in), then the problem must lie elsewhere. I recall one thread from years ago where someone traced rough running to something jamming one of the valves open, so just approach this with systematic testing and see where it leads you rather than throwing parts at it.

Edit: One more random thought, I wonder if vacuum leak(s) on those two cylinders could cause these symptoms. Did you put in new rubber seals on the injectors AND did the injectors seat properly? (Pedantic addition, be sure to coat those seals with Molykote DC-111). Sometimes the fuel rail with all injectors attached makes it hard to get all injectors to seat properly and simultaneously. There are other potential sources of leaks. I don’t think we know the history on the car, was it running well in the past and something changed? If all else fails consider doing a smoke test, but start with checking spark, and inspecting plugs.

Hope this helps. Good luck!

 

rj....thank you for the input! I,ll hit on your bullets and update what has been done.

1.. definitely getting good spark to all cylinders ,even 7 and 8. Those plugs were actually damp when pulled them this morning,clean but I would say running rich which is interesting since as I said,I can unplug the injectors and it doesnt affect the running of the engine.

2.. All the injector connectors are new, most were broken when I got the car. I bought new Bosch connectors and soldered and wrapped them properly. Noid light shows a good signal to all 8.
3.. I did not check the " big connector" on the CE panel.
4.. rechecked cam cover grounds..they were clean but I cleaned them again.
5.. Injectors..... I dont think they were installed in the same way they came out...same side,yes but not same cylinder I,m sure. The report from Witchhunter on these 4 showed all flowing between 229-235 cc per minute and good spray pattern. Pulsed flow between 105.5 and 108. Seems ok and they did note that it took a week in the cleaner to get them from poor to good. The other 4 were about the same.
All received new rubber seals and hoses when I re-installed them, but its possible the back 2 are not seated properly.....I will have to check.

and as far as the history of the car...PO said it ran ok until it just died 1 night on the way home from work....but I am fairly sure thats not the real story. I bought it -non running( never owned a Porsche and thought this would be a fun way to learn about them. That decision definitely damages my claim that I,m not crazy, but Mom had me tested and they said I,m not! ).....it fired on starter fluid at his garage.
I brought it home and after doing some digging found both caps that plug the DE-Cel ports on the throttle body were gone. I plugged that major leak and the car fired. And since I have been plugging away at it as time permits. It has always had the cold starting issue and the rough idle and thats what I have been chasing. When its warm it will fire and sit and idle all day, drive it down the street and you can tell its down on power and not firing on all 8. I do have receipts back to 2010 for all work done on the car and that includes timing belt, Air flow sensor, plugs,wires, suspension work etc.... so it has had some love, but its also had a hard life. I think alot of 928s fell in to the same boat......decent solid cars that were just neglected or worked on by folks that had 0 mechanical ability.

 

Yeah, it's really sad how many of these cars get neglected and/or "repaired" by folks with no skills and/or with bad parts or bandaids. It was as true back in the day as it is now. I remember shopping for two-to-four-year old 928s back in the day and most of them had already been trashed.

Your flow numbers are good, pretty close to what mine were (I posted a pic in the other thread). And a wet plug means fuel (good) but not combustion (bad). And probably also rules out a vacuum leak as a problem, or at least if there is a leak it's not causing the lack of combustion.

Is it possible the spark plug wires for 7 and 8 are swapped? Are both plugs gapped OK? How's the cap look on those two cylinders?

Not sure what else I can suggest for you right now. Are you sure nothing fell into the injector hole when you had the injector out? Of course it's possible that something got in there a long time ago. But before we start talking boroscopy let's stick with the basics!

Please keep us updated and good luck!

 

Just reading through the thread for the second first time, and notice that the third leg on the must-haves-to-run hasn't been checked. Or I missed it. Got warm compression numbers to share? All plugs out, ignition fuse removed (cuts off the injection by default), and the battery maintainer attached to keep battery voltage up. Throttle propped full open for testing.