Excuse the crappy video, and the screen glare, but here is a short video of an oscilloscope connected to my fuel injector harness.

1985 Porsche 911 Oscilloscope Video - YouTube

Is that with the engine running? Idling?
Why is the waveform cutting out towards the end of the video? Real or scope issue (poor triggering)?
What is the total duration of the injection pulse? Looks like less than 1millisec?

What is the diagnostic conclusion for this video? Can you put it into context to understand why are you showing it?

What is that dropout in the hold pulses? That can't be normal.

http://forums.pelicanparts.com/uploa...1345392335.jpg

The video was taken at engine idle, before we took it out on the road and got it to stall. After we got back, we hooked the o-scope up to Mark's 87 944, just to see what it would look like, realizing the 944 and 911 are not the same. The 944 didn't have the subsequent pulses, it looked similar to a heart-beat on an EKG, without the thick bands in-between.

hard to see a drop out or even graticule (hold = <1.7ms?). - decent shot for in the field, but can you open up the time base a bit on the scope? Maybe vary the rpm so you get a feel for yourself.

The "band" is the hold phase produced by the peak&hold driver. The 911 3.2, 924 and early 944 all use the same driver circuit do deal with 4 or 6 low-impedance injectors in parallel. The hold phase is required to reduce the current through the injectors while keeping them open.

Late 944 and 964,993 and onwards have high-impedance injectors driven sequentially. They don't need a peak & hold. They use a simple low-side switch. On the scope you will see a solid pulse for the injection duration. Simple rule: if the DME is a 35 pin version with 2 rows of pins you will see the "band". If it is the 55 pin version with three rows of pins there is no "band".

Ingo

Greetings once again,

I should receive my new injectors today from Motorman. I'm reviewing the instructions in the Bentley manual and want to make sure I get this right:

LEFT SIDE:
1) Remove heater tubes, heater blower fan and heat exchanger feed tube
2) Remove fuel rails by:
A) Disconnect left fuel rail supply and return lines
B) Cut wire ties, and disconnect injector harness connectors
C) Remove fuel rail mounting bolts
D) Carefully pull up on fuel rail and remove injectors
3) To remove each injector
A) Remove locking clip holding each injector to fuel rail
B) Pull each injector from the rail
4) Replace each injector
A) Connect to fuel rail
B) Insert locking clip
5) Re-install fuel rail, tighten to 5.5 ft lbs.

RIGHT SIDE:
1) Remove air filter housing, filter, element
2) Loosen bolts that hold A/C compressor in place, remove belt, place compressor on towel near bumper.
3) Follow steps 2 - 5 from LEFT SIDE.

Questions:
1) Does the system have pressure when the system is off? If so, can I do anything to remove the pressure to the fuel lines?
2) How difficult is it to remove the U shaped clips from the injectors, which allow the injector to be removed from the fuel rail?
3) How much fuel should I see when i disconnect the fuel supply/return lines?
4) How much fuel should I see when I remove the injector from the fuel rail?
5) Any other tips?

As usual, thanks in advance.
Scott

You will see fuel at all 4 places that can easily be collected on a rag.

You can take the clips off with your fingers.

I'm not sure pulling the fuel rail out with the injectors attached is going to work. I ended up removing the clips and pulling the rail off the injectors and then pulling the injectors one by one. Some were glued in there pretty good. I put them back in installed in the rail however.

1. When you crack a line, pressure will bleed off rapidly until the damper and regulators pump down.
2. I use needle nose. They aren't hard to remove, just sheetmetal.
3. Not much, a couple/few rags will do
4. Very little
5. Patience and wiggle everything gently. It'll work free. Use vasoline on the new o-rings to aid assembly back into rails and intake bosses.

6 new-to-me fuel injectors, courtesy of MotorMan in Michigan. Ordered on Friday, received in NJ on Monday. Installation will occur either tonight or tomorrow. Details thereafter regarding success or failure of my stalling issue!

http://forums.pelicanparts.com/uploa...1345484184.jpg

I would advise against vasoline on the o-rings...petroleum jelly will deteriorate those o-rings! Use a good silicone lubricant.

Can someone give me an example of a good silicone lubricant? Originally my plan was to use motor oil (Mobil-1) on the o-rings, but if I should keep away from petroleum jelly, I assume I should also keep away from motor oil. What about WD-40?

Gas is the recommended lubricant. Dip the top when you put them in the rails and slop some around with a brush on the manifold.

Not sure if motor oil is a bad choice - it would have been my first guess. Gas sounds good, too.

I really like Hylomar blue from Permatex as gasket dressing on O-rings of all sorts. It is non-setting and keeps the O-rings lubed for years. Unfortunately, there is rumor it was discontinued? I grabbed several tubes a while back. Check your LAPS (local auto parts store) if they carry it.

waiting in anticipation for whether the new injectors fixed the issues you are having.....

Ingo, Hylomar (original brand, not Permatex) should be plenty available as our jet engines specifically call out for it and in aviation you cannot deviate.

Greetings folks,

Here's an update. Tonight, I installed the new fuel injectors, and went for a test run. I banged thru 1st, 2nd, 3rd and into 4th, and it didn't die (normally it would die at 5k RPM's in 2nd or 3rd). Then I turned around, and started to come home. This time, at 5k RPM's, it didn't die, but it started to hesitate, so I downshifted and came to a stop. At this point, the car was idling very erratically, and eventually died. The engine sounded like it was running on 5 injectors. Each time it stalled, it started right back up (something it didn't do before), but again it wasn't running right, so I limped home. When I got into my driveway, I began to check the injector wires, pulling each one off, then reconnecting it. Eventually it began to run better. I revved the engine and it sounded fine.

Since it's now dark, I'm calling it a night, but I'll check the injector wires tomorrow and make sure I did the installation correctly, but this is much different and in my opinion, much better than it has been, as it didn't die (like turning off a light switch), and each time it did stall, it started right back up. More to come...

Greetings folks,

Here is yet another update to my never ending saga of the stalling 911. Last I told you, I replaced the injectors, took it for a spin, and this time, instead of the car dying at 5k RPM's in 3rd, it started to run erratically (i.e. like running on 5 cylinders). When the car got into this state, at idle, it would run like it was missing. So, tonight, Mark and I hooked up the o-scope to the injectors again, just to see what happens when it gets into this new state. When the car began to miss at 5k RPM's, the injector pattern in the scope did not change. This of course, is different from last week, when the injectors flat-lined. So it appears we did fix one problem, but discovered something else. Next we connected a fuel pressure gauge to the fuel rail and did a pressure test. At idle, the fuel pressure was 38lbs, when we took off it stayed at 38lbs, but then when the car went into that "funky state" where it appears to be running on 5 cylinders, the fuel pressure spike the meter at 100lbs. Could this indicate a bad fuel pressure regulator (as Otto stated last week), or is it a bad fuel damper, or both.

As usual, any and all suggestions are welcome. One more question, does the fuel pressure regulator from an 87 944 (part # 944-110-198-03-M14) work in an 85 911 (part # 928-110-198-01-M14)?

Thanks.

Look into the fuel return line too. If it can't drain fuel back to the tank, fuel pressure can go up.

Scratch that, the issue would be worse at lower RPM's than higher.

The fuel pressure regulator is also supposed to regulate the pressure relative to the manifold absolute pressure. When you open the throttle the pressure you measure relative to atmosphere should go up. :)

I am recalling the no-run, unplugging ANY one of the injectors and it runs scenario.

That seems to say less current is required and it runs. Only two paths it could be, positive or negative. Please check all ground wires around the manifold. Maybe even put in a few temporary ones as a test. If that fails it must be the positive side.

Techman1,

We have checked all the grounds, and then re-checked them by three different people. That is one area we feel confident about. Is it your belief the ground could cause the fuel pressure to spike the meter? If so, please provide more detail, as I don't understand how it could (not saying I'm an expert, actually just the opposite). This has been quite a learning experience for me.

Thanks,
Scott

Not sure, but a guess would be the normal flow of the injectors stopping would cause a pressure surge before the pressure regulator caught it.

Is the surge noticed in advance of the stumble/shutdown?

Ingo, where is the current coming from in the DME to drive the injectors? Are there any wires to the DME that provide an internal ground, for that purpose? Just trying to think out of the box!

Not in the field as a pro, but love fixing problems!

"At idle, the fuel pressure was 38lbs, when we took off it stayed at 38lbs, but then when the car went into that "funky state" where it appears to be running on 5 cylinders, the fuel pressure spike the meter at 100lbs. Could this indicate a bad fuel pressure regulator (as Otto stated last week), or is it a bad fuel damper, or both."

Glad you found your problem. It's unfortunate that you got persuaded into replacing so many
parts especially the rebuilt DME ECM and the "rebuilt" injectors. But that's what happens
when the shotgun troubleshooting approach is used.

So now you need to replace your fuel pressure regulator, as it's sticking causing the high
pressure which in turn kills the engine. When the engine is accelerating under heavy load
the fuel demand in high causing the fuel pressure regulator to allow more fuel. When the
load/RPM is reduced, the fuel pressure (amount of fuel) doesn't return to the normal value
since the regulator stayed at the high pressure setting. The accumulator is not the problem.

Greetings,

So with my new issue whereby the fuel pressure goes from 38lbs to 100+lbs under heavy acceleration (3rd gear, 5k RPM's), how can I tell if the Fuel Pressure Regulator (FPR) or the Fuel Pressure Damper (FPD) is the culprit. As a side note, when the car gets into this condition whereby the pressure exceeds 100+lbs, the engine does not stall, but runs erratically (too much fuel I guess), and as I idle, the fuel pressure s l o w l y decreases back to the high 30's of pressure.

Since I'm getting tired of buying parts w/o results, I want to make sure I order the right part. Also, I can only see the FPR for an 85 3.2, not the FPD.

Thanks.

Scott: The FPD function is to even out the hydraulic fuel pulses caused by the injectors switching on and off. Really doesn't have anything to do w/your fuel pressure.

Agree w/Otto it's a fuel pressure regulator issue. Before replacing, however, check FPR function using the procedure in the Bentley manual. I'd be willing to bet (50/50 chance or better) that you may have a vacuum issue. The FPR uses engine vacuum against a diaphragm to regulate fuel pressure in relation to engine load (low vacuum/WOT = high load; high vacuum [idle, closed-throttle decel] = low load).

Based on your description of symptoms, it's possible you're not getting sufficient vacuum to the FPR vacuum port under decel conditions to reduce fuel pressure following your high-load/low-vacuum condition. Check the vacuum hose (condition, split, etc.); might even want to put a vacuum gauge on the end of the hose to make sure. IMHO worth checking this before springing >$100 for a new FPR. If nothing else will give you some peace of mind if/when you do replace FPR.

Hope this helps.

Dale

"So with my new issue whereby the fuel pressure goes from 38lbs to 100+lbs"

This is NOT a new issue. It's the same issue you've been having from the
beginning with just slightly different symptoms, i.e. the engine either stalls
or dies after continued hard acceleration. All the wasted time and money
(DME rebuild & injectors) could have been avoided by just monitoring the
fuel pressure as was suggested and not following all the typical mis-guided
info!

"it's possible you're not getting sufficient vacuum to the FPR vacuum port"

More mis-info, as the vacuum only affects the fuel pressure by a few PSIs.

Otto,

You're on the left coast, and I'm on the right coast, I needed you over here....

Thanks for your help. I'm heading out on vacation for a week, during which the fuel pressure regulator should arrive, thus the week after next I'll install it and hopefully be done!!! Of course, I'll provide a status update afterwards.

Now it's time to slip into a dry martini and forget the week!!!
Enjoy all,
Scott

Hey Otto,
Do you really think those injectors were functioning correctly with the waveforms they presented? Is there always only one thing wrong with the cars you work on? This one so far has had wiring issues, injectors and now fuel pressure.

The only thing I worry about your pressure regulator is a restriction in the return hose that flows the volume at idle but won't flow the reduced amount when you get on it.

While I would've encouraged a bit investigation prior to the purchase of all 6 injectors, I still think Scott made the right move. The stalling has stopped and presumably there is no more flat-lining of the drive signal. And there was the issue with the short in the relay socket, so I don't think all of the problems were/are related to just one cause (FPR).

Here we are at post #188 and the fuel pressure regulator problem gets found.

I did suggest this in post#68 since I worked on a car with identical symptoms.

Then, once again the same suggestion came up on post#14.

***** NEWS FLASH *****

After one year, countless part swaps/installs/replacements, diagnosis's, missed diagnosis's, re-diagnosis's, my 1985 Porsche 911 Carrera Targa is fixed. Tonight we replaced the Fuel Pressure Regulator (what a b*tch that was to get to...), cleaned up the vacuum lines between it, the Damper and the throttle area, and took it for a spin. The car was very responsive, and plowed thru the gears, shifting at 6k RPM's. We drove it for a while in a very "spirited" movement, and no problems, no stalling, no rough idling. It drove as it should and probably better than it's ever driven before.

I want to thank everyone who followed this thread, who provided suggestions, encouragement and perseverance, as this got me thru this very very long learning experience, something I don't want to repeat, but am the wiser for going thru it. I have not added up the costs yet, and I just may leave it that way, but over the year, I ended up doing quite a bit of "preventive maintenance..." if you will. I now have about 2 hours of clean-up work to do, and then I'll be ready to wash, wax and polish the car. I may even treat it to a new set of tires in the spring, as this years Porsche kitty has been spent...

Thanks to all!! I could not have done this without the Pelican forum members.
Scott

Congrats! So in a nutshell, there must have been a groove that developed in the FPR that would cause the diaphragm to stick, fuel pressure building up, and then the motor would be given a good dose of 100 PSI of fuel pressure causing it to die.

Good to hear you're back on the road.

:)

For those who may need this, I have the correct fittings to the fuel rail to test fuel pressures using either hose..........

http://forums.pelicanparts.com/uploa...1347110265.jpg

or Polyamid tube.......

http://forums.pelicanparts.com/uploa...1347110322.jpg

or as part of a complete Fuel Pressure Tester assy......

http://forums.pelicanparts.com/uploa...1347110362.jpg

The Poly line shown above is long enough to bring up front to the pass compt to monitor fuel pressures while driving.

Please email me for info.

Thanks, Have a great Porsche day everyone.

Len

:)

Full Throttle loss of power
 

Hi, I found this thread about your issue you finally got resolved, incredible. I have an issue that I have not been able to resolve and it’s a bit different than yours. My car is a dedicated 1985, 3.2, race car, with open exhaust. About 4 months ago I developed a partial loss of power only at full throttle, can happen from 6000 to 7000 RPM, when it happens you feel the car stop pulling as hard and hear the pitch in the exhaust change, when it happens sometimes after a second or 2 it will clear itself out and if it doesn’t 50% of the time lifting the throttle and going back to full throttle will clear it, sometimes I have to lift off the throttle a few times to clear it. When it happens I can also lift off the throttle say 400RPM and hold it there and it clears out and then going back to full throttle also clears it out 50% of the time as well. It can happen once a lap to several times a lap to not happen all day to happen all day, it can happen in the first session of the day or the last session of the day, it can happen if the air temp is 60 degrees or 100. Very hard to isolate because it is so intermittent and won’t happen on the dyno.

I have a fuel pressure gauge and when it happens the fuel pressure is unaffected.
The DME has been checked out and I have tried a different DME,
I have also replaced: coil, fly wheel sensors, temperature head sensor, throttle position sensor, air meter, DME relay, spark plugs, plug wires, rotor, cap

Not sure what to try next, but feels full related as the loss of power is smooth, does not miss and stutter like an electrical miss might. Any input would be great.