excellent way to test injectors on 78 911

[stormcrow]

Gazzerr,

I believe you should be able to flex them a little. Best way is to disconnect the tubing from injector before you remove the injectors if at all possible.

Then you can reconnect the injectors to test them. I know it's a PITA but it's better to be safe. The lines may have some flex but you need to be careful not to kink them.

Someone else with the steel lines might chime in to further clarify.

[2jmotorsports]

Originally Posted by stormcrow

Those fuel lines came off a VW Jetta I believe. I happen to be at a junk yard and noticed that the VW Jetta has the injection system similar to ours so I managed to salvage some parts off it.

I also salvaged a pressur regulator and it is presently installed on my engine.

Pardon the question but are you running the VW lines and regulator only during testing or full time in place of the hard lines?

[JSV798]

Surely the fuel pump is not supposed to run with just the ignition on and the engine stopped; it doesn't run on my car until the plate is lifted which happens when the car starts OR when the key is turned to the start position.

[timmy2]

Originally Posted by JSV798

Surely the fuel pump is not supposed to run with just the ignition on and the engine stopped; it doesn't run on my car until the plate is lifted which happens when the car starts OR when the key is turned to the start position.

You are correct, the pump shouldn't run with ignition on and the car not started.

For testing fuel injector flow/pattern/leakage the pump is forced on by jumpering the relay socket or disconnecting the safety air flow switch on the back of the metering body to enable the pump running for the tests as per factory methods to confirm injector specifications.

[stormcrow]

2j,

I have permanently installed the fuel lines and regulator. I modified the regulator so I can adjust the pressure on the system. Never had an issue since they have been installed several years ago.

[gazzerr]

Thanks Steve appreciate the advice. I'll give it a go. G.

[grantsmells]

Gazzer i did the test with my solid steel fuel lines, was just very careful to move them slowly and only as little as i could get away with. Just as Steve said, i disconnected the fuel line from injector, then removed injector, put it in a bottle, found the best place to sit the bottle, then carefully moved and reattached the fuel line.

Originally Posted by stormcrow

When you do the test you need to test all the injectors at once, otherwise raw fuel will be injected into the cylinders and that's not good.

Steve could you please elaborate on 'not good'? Should i be checking my oil for fuel after doing this test twice with 5 injectors still in? And as you'll see in a second, i think a fair bit of fuel will also have gotten into my cyl #5 over the past few weeks while i've been trying to diagnose my problem.

And here are my test results:

i followed your advice Steve and tested them all together (albeit a bit late) and with the air sensor plate closed 1,2,3 &6 didn't even drip, but 4 sprayed a little, and 5 sprayed a lot, then i pushed the plate up for a few seconds, which showed 1,2,3,&6 to run fine.

So here come my questions:
1)Would i be correct in assuming it's a pretty good chance this is why my cyl 4 & 5 haven't been firing?
2)Is this definitely an injector problem? or is there a chance it's a fuel distributer problem?
3)After having them cleaned and tested, if one or two injectors need replacing with brand new, can i get away with replacing just the one or two? or will i need to replace them all at once?

Thanks for any and all help and advice!

[74-911]

Originally Posted by timmy2

You are correct, the pump shouldn't run with ignition on and the car not started.

For testing fuel injector flow/pattern/leakage the pump is forced on by jumpering the relay socket or disconnecting the safety air flow switch on the back of the metering body to enable the pump running for the tests as per factory methods to confirm injector specifications.

Note: for anyone with a '74 911, who is following this thread, the fuel pump on a '74 does run when the key is turned to the "on" position.

[fintstone]

Originally Posted by grantsmells

G...

So here come my questions:
1)Would i be correct in assuming it's a pretty good chance this is why my cyl 4 & 5 haven't been firing?
2)Is this definitely an injector problem? or is there a chance it's a fuel distributer problem?
3)After having them cleaned and tested, if one or two injectors need replacing with brand new, can i get away with replacing just the one or two? or will i need to replace them all at once?

Thanks for any and all help and advice!

Yikes! Lucky it even turns over with so much fuel in a cylinder. Easy way to check, just swap your injector (or line and injector) with one of the ones that are working normally and do the test again...see if the problem moves to a different cylinder.

[gazzerr]

Thanks very much for sharing that Grant! I'll test mine this weekend if I can find the time. I'm very interested to see what your problem is there. My injector seals are shot so I want to replace those. They are all leaking with the carb cleaner spray test.

[stormcrow]

Grant,

Yes you do have an issue on injector 4 & 5. I would do a single line test using any other line then 4 & 5. You can also swap out injectors on both lines with good objectors to see what happens.

Looks like the other injectors are ok as long as they are not leaking and I don't see any reason not to change out just those two. But I would do a comparison test after you install the new ones to make sure your fuel flow is the same for all injectors.

From what I remember the injectors should open around 32 PSI. As far as the fuel distributor goes there could be a problem with the rubber O ring that goes around each injector slot internally on the fuel distributor. If it is leaking by then yes that could be the issue. Lots of things to check beforehand without dealing with the fuel distributor.

[grantsmells]

I did the switcharoo test, and found that with whichever injectors i used, cyl 4 & 5 are still the lines that are leaking. So the fuel distributer came out yesterday. I'm going to attempt to clean and/or repair it with a rebuild kit with help from this thread CIS fuel distributer cleanout w/pics before i give up and get a rebuilt one.

But here's another question: I was going to send the injectors off to get cleaned anyway, but the best price i could find here down under is $45 each, with no guarantees. So i think i'll just soak them in some injector cleaner. and finally to the question, can i blast these with baking soda to clean the outsides and inside the cone bit where it connects to the fuel line? or could the baking soda be bad for them? i didn't want to use anything more abrasive or i'd probably end up with bits of sand or media clogging the injectors.

[boyt911sc]

Originally Posted by grantsmells

Gazzer i did the test with my solid steel fuel lines, was just very careful to move them slowly and only as little as i could get away with. Just as Steve said, i disconnected the fuel line from injector, then removed injector, put it in a bottle, found the best place to sit the bottle, then carefully moved and reattached the fuel line.

Steve could you please elaborate on 'not good'? Should i be checking my oil for fuel after doing this test twice with 5 injectors still in? And as you'll see in a second, i think a fair bit of fuel will also have gotten into my cyl #5 over the past few weeks while i've been trying to diagnose my problem.

And here are my test results:

i followed your advice Steve and tested them all together (albeit a bit late) and with the air sensor plate closed 1,2,3 &6 didn't even drip, but 4 sprayed a little, and 5 sprayed a lot, then i pushed the plate up for a few seconds, which showed 1,2,3,&6 to run fine.

So here come my questions:
1)Would i be correct in assuming it's a pretty good chance this is why my cyl 4 & 5 haven't been firing?
2)Is this definitely an injector problem? or is there a chance it's a fuel distributer problem?
3)After having them cleaned and tested, if one or two injectors need replacing with brand new, can i get away with replacing just the one or two? or will i need to replace them all at once?

Thanks for any and all help and advice!

Grant,

The six (6) bottles show the big discrepancies between 1,2,3 & 6 and 4 & 5 bottles. These were caused by defective fuel flow specially in 4 & 5 with defective o-rings. They get old and brittle and eventually breaks apart due to age.

Several ways to check and test your fuel flow:
a). Six (6) fuel lines without injectors. This will test the fuel lines integrity. A restricted fuel line would delivery less volume.
b). Six (6) fuel lines with injectors installed. The injectors should have very close opening pressures, otherwise it would affect the volume.
c). Calibration and testing of the flow rate is done without the injectors to reduce the variables. Earlier FD's models no adjustment capability.

Going back to your flow rates:
a). Lines 1,2,3, & 6 are OK.
b). Lines #4 & #6 are leaking due to crack/s or split in the o-ring around the slit.

Your FD has to be rebuilt to get it to work properly. A FD in good working condition should not deliver fuel when the plunger is down. A tiny drip once in a while is acceptable. If it drips twice in a 3-min. period, that's a good sign of o-ring deterioration. Keep us posted.

Tony

[stormcrow]

Grant,

It appears the issue is with the fuel distributor. Not that hard to rebuild as long as you pay attention. As far as rhe injectors go it appears they are working fine. All the flow rates are the same except with 4 & 5 which is related to the fuel distributor.

As far as cleaning the outside they are only discolored not dirty so I wouldn't worry about that just soak them with injector cleaner and make sure after soaking they are again flushed with clean FIRST cleaner. Get your fuel distributor working properly. You are making good progress.

[grantsmells]

Thanks for your advice guys, i opened up the FD today expecting to find a hole or split in the diaphram, or something broken, but everything inside looked really good. None of the o-rings were broken or split, but most of them are a little hard and a bit loose around the spring as you can see in the photo. but they all still protruded from the spring, i can't see anywhere obvious they'd be leaking from.

Now, i'm still getting my head around exactly how the FD works. I thought those 6 o-rings were only to hold the fuel in when travelling from the centre piece into each upper chamber. But after what you've both just said, i had a closer look, and if i'm right, the fuel is actually constantly surrounding those o-rings too? no matter what position the plunger is in? Which now makes sense to me why a leaky o-ring (or 2) would cause the fuel to leak out like it is.

My other concern though, is my plunger. I was very careful not to drop it or scrape it or anything, but there are some very fine scratch marks on it that i can feel if i run my fingernail over it, that i fear also could be letting fuel in. ALTHOUGH there are corresponding scratch marks on the inside of the piece it sits in (the bit in the above photo, dunno what to call it) right near the slits, BUT not anywhere near the slits for cyl 4&5, it's closer to 1&2.


I'll get some new fresh o-rings, but do you think i need a new plunger? Seeing as it seems the scratches were in the wrong spot to be causing my problem. I'd like to replace it, and that centre part it sits inside, but i don't know how easy it will be to find them here in not-particularly-European-car-friendly-Australia.

[grantsmells]

I probably should be starting a new thread for this, but you guys seem like you know what you're talking about, so i'll stay here for now...

[stormcrow]

Grant,

Tour problem could be with the individual pressure adjustment screws that are on top of the fuel distributor. But before you make any adjustments do a search on bosche fuel injection systems and how the fuel distributor works.

There is a pressure differential between the top of the plate and the bottom of the plate. Those screws control the pressure differential. Should you decide to make an adjustment only do it on the 4 & 5 ports of the injectors that you are having problems with. Don't touch the other ones.

[T77911S]

check your metal shim, make sure there are no small "dimples" where the valve seate on the shim. (not sure if the 3.0 does this).


now you have to line those tiny slits up with the openings in the top of the FD. good luck.
the other thing is oil or grease all the rubber parts when putting it back together,
also, that metak shim and the 2 halves have to be VERY clean. no gasket sealer.

you could have also done the test without the injectors. the results may not be as close as they would be with the injectors but if your FD was bad (#5), that would show up.

[boyt911sc]

Originally Posted by grantsmells

Thanks for your advice guys, i opened up the FD today expecting to find a hole or split in the diaphram, or something broken, but everything inside looked really good. None of the o-rings were broken or split, but most of them are a little hard and a bit loose around the spring as you can see in the photo. but they all still protruded from the spring, i can't see anywhere obvious they'd be leaking from.

Now, i'm still getting my head around exactly how the FD works. I thought those 6 o-rings were only to hold the fuel in when travelling from the centre piece into each upper chamber. But after what you've both just said, i had a closer look, and if i'm right, the fuel is actually constantly surrounding those o-rings too? no matter what position the plunger is in? Which now makes sense to me why a leaky o-ring (or 2) would cause the fuel to leak out like it is.

My other concern though, is my plunger. I was very careful not to drop it or scrape it or anything, but there are some very fine scratch marks on it that i can feel if i run my fingernail over it, that i fear also could be letting fuel in. ALTHOUGH there are corresponding scratch marks on the inside of the piece it sits in (the bit in the above photo, dunno what to call it) right near the slits, BUT not anywhere near the slits for cyl 4&5, it's closer to 1&2.


I'll get some new fresh o-rings, but do you think i need a new plunger? Seeing as it seems the scratches were in the wrong spot to be causing my problem. I'd like to replace it, and that centre part it sits inside, but i don't know how easy it will be to find them here in not-particularly-European-car-friendly-Australia.

Grant,

I just did three (3) FD rebuilds. Two (2) yesterday and one (1) today. Those o-rings around the slits are flat looking already. Toss them away and install new ones. That abrasions on the plunger does not look good but as long as it does not bind and leak, you could use it. Slide the plunger through the barrel (lubricated) up and down. See if the plunger slides down by its own weight. Feel the resistance if any. That plunger should slide freely or atleast with a very minimal push to slide it.

If you need some parts for your FD, go visit your local auto yard. European cars (Volvo, Saab, MB, BMW, etc.) in the 80's used CIS and plunger is a standard or common part in a Bosch FD.

Tony

[grantsmells]

Thanks Tony, i was hoping they might be generic, and the plunger would be exactly the same dimensions in all those makes of cars, whether 4,6 or 8 cylinder?
When i pulled the FD out the plunger was dropping under its own weight easily, i sat there pushing it up and letting it drop a few times just for amusement (yea, i don't get out much) and didn't feel any binding at all, i've read not to sand or polish the plunger, but in my case would i benefit from rubbing a bit of wet&dry 1200 very lightly just on the scratched area? or would i be better to just leave it as is if i can't find a new plunger?

Originally Posted by T77911S

also, that metak shim and the 2 halves have to be VERY clean. no gasket sealer.

thanks for all your advice, i've read otherwise on this though, many people have said to use loctite 574 or similar in a very thin layer on both upper and lower surfaces but not on the diaphragm itself. Have you done this yourself without sealant and had it not leak?
Tony, do you use a sealant?
Do i just use clean engine oil to lube the o-rings and plunger? I've also read to use silicon lube, but i have engine oil lying around already if that will do the job.