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Old 05-20-2009, 12:48 AM   #1
oldschoolvolvo
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Question kjet injector pulsing

Car: 1979 242DL
Mileage: 210,xxx

Backstory:
I've been fighting a progressively worsening problem of my car feeling like it's missing significantly whenever there is load on the engine. Going up hills, accelerating through the gears, etc. It has gotten very bad recently, and is not very drivable when it's acting up. However, sometimes you can start it up and drive it and it will just miss a little and is still driveable.

Today I pulled the injectors to look at the spray pattern and when I was testing them, sometimes they would spray fine and other times they would spray in pulses, which would explain why the car acts the way it does. All injectors would pulse in unison. The fuel pumps were not pulsing or anything and I think whatever is causing that is the root of the car's problem. Is something getting stuck in the fuel distributor? I have had both fuel pumps and fuel filter changed in the last year so I think they're fine.

Any thoughts?
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Old 05-20-2009, 01:07 AM   #2
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dirty fuel distributor?
Check k-jet.org there is lots there, more than you need and GOOD info too.
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Old 05-20-2009, 01:18 AM   #3
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was it spraying in pulses while the air metering plate was being held still? or as it was moved? my thought is that as you are trying to accellerate, the piston that moves with the metering place isn't moving smoothly. i'm not sure what else could cause the fuel pressure to pulsate...

fuel dizzy seems like a likely culprit, i'm just not sure how. put a pressure tester on it.

and check kjet.org out
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Old 05-20-2009, 01:23 AM   #4
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Kjet injectors do not pulse. The frequency valve pulses. The fuel pump pulses.


Sounds like your fuel pump is going south.
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Old 05-20-2009, 01:46 AM   #5
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Sounds like your fuel pump is going south.
this was a thought of mine as well, but you said it's good. how do you know the pump wasn't responsible, did you have somebody physically touching the pump while you were checking injector pattern to confirm that they weren't pulsing in unison?
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Old 05-20-2009, 02:11 AM   #6
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k-jet = pressure gauge.

My k-jet fuel pumps do not pulse.

Check the fuel pressure at the filter, my 78, 245 runs about 105 psi static pressure. That is hooked to the gauge and nothing else.

k-jet injectors just have varying amounts of cone spray which is very fine and they also sing like a sick bird.

k-jet is all about pressure.

k-jets are great.

Last edited by moxy123; 05-20-2009 at 02:17 AM..
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Old 05-20-2009, 03:24 AM   #7
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k-jets are great.
i was right there with you until this part
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Old 05-20-2009, 10:39 AM   #8
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Quote:
Originally Posted by PRVersion View Post
was it spraying in pulses while the air metering plate was being held still? or as it was moved? my thought is that as you are trying to accellerate, the piston that moves with the metering place isn't moving smoothly. i'm not sure what else could cause the fuel pressure to pulsate...

fuel dizzy seems like a likely culprit, i'm just not sure how. put a pressure tester on it.

and check kjet.org out
the injectors would pulse when i would hold the metering plate steady. i also moved it up and down to see if that would change anything but it just changed the amount of fuel coming out, still pulsing.

i could hear the fuel pumps running and they sounded normal.
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Old 05-20-2009, 11:00 AM   #9
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i don't know much about K-jet but i suppose the system uses a prime-intank-pump and a pressurepump, right?
If so, maybe the intank pump has gone south. That would mean the pressurepump needs to pump air in order to draw fuel from the tank.
maybe this is what causes the pulsing? (air>fuel>air>fuel etc.)
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Old 05-20-2009, 02:24 PM   #10
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When I had intermittent operation of a kjet car. It always turned out to be something with the main pressure pump. Either a bad accumulator that no longer absorbs the fuel pump pulses and leaks. Or a bad main pump that is intermittent. I've also had intermittent fuel pump relays cause strange stuff, too. But the most frustrating of all was when I had an intermittent pump that seemed to run fine but was actually screwing up. For kjet testing with anything suspected you need to get a gauge on there. You can even drive with the gauge so when it starts screwing up you can pull over and check your pressures.
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Old 05-20-2009, 02:33 PM   #11
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yea i'd be interested to check my fuel pressures, but do you basically have to put together a gauge system from scratch?
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Old 05-20-2009, 02:39 PM   #12
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JC Whitney and IPD used to sell somewhat affordable kjet gauges. Maybe they can order something for you? The only place I know of now that stocks a kjet gauge wants around $200 for it. That is Pelican Parts in the Porsche tools listings. You can make up a gauge setup that works. It has to be at least a 6-8 bar or 100psi gauge. The gauge is setup in the hoses with the gauge on a T fitting. The T fitting must be the type with a valve so you can set it so it blocks fuel flow but not to the gauge and also opens to allow fuel flow but still not blocking the gauge. Of course the ends of the hose need to be banjo fittings matching the hose that goes from the center of the fuel distributor to the control pressure regulator.

That enables you to check system pressure, control pressure, and rest pressure. The three most important pressure checks in kjet.

Make sure the test setup you make has good secure connections because you are working with about 75psi system pressure which is serious and dangerous. Be sure you use only high pressure rated fuel injection hose and good clamps that don't dig into the fuel hose.
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Old 05-20-2009, 02:54 PM   #13
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They sell Bosch CI system gauges as a kit, to do it properly that is what you need. Some kits are cheap and simple but will work others are quality and pricey.

I have in a pinch went to home depot and bought a cheap, $8, water pressure gauge and used that to ball park the main fuel pressure. 0-150 psi, and it worked to get an idea for that part anyway.

k-jet runs with a high pressure tolerance and to check everything you need a gauge. Can you tell if a battery is charging properly without a voltmeter?

The injectors have a pressure regulator in them as well and need the correct pressure supplied to them to work or they will do exactly as you describe.

The most basic thing to do first is check the pressure at the fuel filter. If it is close then fill the fuel filter full of Sea Foam and then reconnect everything. Squirt the injectors for a short while and stop for a minute or two and repeat. Try to let the Sea Foam soak free the debris over a half hour or so. k-jet has no tolerance for sludge.

Last edited by moxy123; 05-27-2009 at 07:10 PM..
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Old 05-27-2009, 02:51 PM   #14
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anyone know what size threads the fuel filter has? i have a gauge but i need to get some fittings to hook it up.
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Old 05-27-2009, 05:48 PM   #15
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I have been dealing with this same issue on my '84 and have replaced both pumps during the process. I never got pressure readings, but was able to fix it the first time by draining the tank, then driving the car about 6 miles with about a gallon or so of fresh gas with a full can of seafoam...suddenly it ran perfect. All was well for about 3 tanks, then I thought I got another bad tank because it started to do the same thing again. My car would idle fine then misfire, then idle fine over and over in a very timed pattern. The misfire was really bad and the wideband was going full lean when it would happen, so again I thought bad gas, sucking water, etc. I finally drained the tank again and let it run with a little bit of new gas / seafoam and after about 5 minutes of idling in the driveway...idle was fine, but the car would miss badly when driven. I pulled the plug wires off and the second cylinder from the front was dead, so I put a plug in the wire and it was firing...injector replacement and swap the plug for good measure and it runs great. I have put about 250 miles on it in the last 3 days without any other issues. Oh, the filter was swapped during all this, too. Hope this helps...sound like your issue is the same as mine. I have a video link on here of the original issue
http://forums.turbobricks.com/showthread.php?t=144656
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Old 05-27-2009, 06:32 PM   #16
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hmm interesting, thanks for the info.

anyone know the thread sizes for the fuel filter? from what i've looked up it appears to be 12mm and 14mm, but i can't find any adapters that would fit. i'd like to just take out the fuel filter and tee in the pressure gauge. does anyone make a 12/14mm female fitting?
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Old 05-27-2009, 06:46 PM   #17
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Old 05-27-2009, 07:20 PM   #18
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With the pressure checked and a good cone mist at the injectors throughout the throttle plate range you have made great progress. Injectors must be clean and function or replace.

The frequency valve does nothing more than lean out the system with pulses from the ECU which is fed from the O2 sensor. With it unplugged it will run rich, that is all. The accumulator dampens the vibration in the fuel line loop but mainly it keeps the loop pressurized for a few days to start quicker after sitting. K-jet must crank a bit otherwise if it sits for days but a failing accumulator does not effect performance after running, the pressure regulator does most of it.

Vacuum leaks need to be fixed if needed too. Starter fluid to find those.
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Old 09-01-2015, 07:30 PM   #19
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6 year bump...haha.

Long story but still trying to get to the bottom of this "missing" issue.

I have recently done some testing to try and determine the root cause of this issue. I pieced together a kjet pressure tester like this: http://www.turbobricks.com/forums/sh...d.php?t=289775 and hooked it up to see what I could find. Per the thread/Greenbook, the line pressure should be 65-75psi and the control pressure should start around 20psi and raise to 45-50psi.

Here's a short video to document:


To summarize, it looks like my control pressure is low...the highest it ever gets is 40psi. I can't watch the gauge while driving so I can't exactly see what's happening when the missing occurs, but it doesn't look like the CPR raises the control pressure to the correct level after warming up.

Any thoughts on the line pressure? Is it normal for it to bounce like that?

I tested the pump head pressure by hooking up my pressure tester to the outlet of the fuel filter. As you can see in the vid below the pressure hovers around 130psi. Again, the gauge needle is not rock solid and bounces...is this normal? The pump is virtually silent during this test (the noise you hear in the video is from insects, not the car).


Pic of test setup.


So after all this testing, what have I learned?
-head pressure is 130psi (gauge needle fluctuates)
-kjet line pressure is 65-70psi (gauge needle fluctuates, corresponds with when the fuel pump makes a buzzing noise, see first video)
-kjet control pressure is 40psi (below Greenbook spec)
-fuel pumps meet the Greenbook flowrate spec

Based on that information, it still looks like the CPR is the culprit.

In the end I want to know that my fuel pumps are working properly. Unless I am missing something, it seems like they are operating normally, besides making some buzzing noises when the car is running.

Kjet gurus...any thoughts or comments?
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Old 09-02-2015, 10:00 AM   #20
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I would make sure your in tank pump is working. Fuel accumulator is supposed to even out the fuel pump pulsing. You can check that also.
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Old 09-02-2015, 10:22 AM   #21
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I would make sure your in tank pump is working. Fuel accumulator is supposed to even out the fuel pump pulsing. You can check that also.
^^

Yes, according to my ears the first video is conclusive the main pump is sucking vapor. And going by the gauge, the accumulator is doing a great job trying to even that out.

You can troubleshoot all that, including the CPR, without running the engine, with a few electrical tricks: See Using the K-jet Fuel Pressure Test Kit
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Old 09-02-2015, 12:15 PM   #22
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Thanks for the replies.

I did replace the in-tank pump recently and it has maybe 250 miles on it. I can hear it run by jumping the fuses and I also disconnected the line from the main pump and verified the in-tank pump was moving fuel. I did not check the flowrate bc I couldn't find a spec.

What is the correct flowrate for the in-tank pump?
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Old 09-02-2015, 12:25 PM   #23
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Quote:
Originally Posted by oldschoolvolvo View Post
Thanks for the replies.

I did replace the in-tank pump recently and it has maybe 250 miles on it. I can hear it run by jumping the fuses and I also disconnected the line from the main pump and verified the in-tank pump was moving fuel. I did not check the flowrate bc I couldn't find a spec.

What is the correct flowrate for the in-tank pump?
The flow rate needs to be the same (or greater than) the flow rate of the main pump in operation, of course, or there will be vapor. The sound in your video is unmistakable, in my opinion.
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Old 09-02-2015, 12:28 PM   #24
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The flow rate needs to be the same (or greater than) the flow rate of the main pump in operation, of course, or there will be vapor. The sound in your video is unmistakable, in my opinion.
Got it, thanks. I will check the flowrate of the tank pump tonight and report back.
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Old 09-02-2015, 12:44 PM   #25
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Quote:
Originally Posted by oldschoolvolvo View Post
Thanks for the replies.

I did replace the in-tank pump recently and it has maybe 250 miles on it. I can hear it run by jumping the fuses and I also disconnected the line from the main pump and verified the in-tank pump was moving fuel. I did not check the flowrate bc I couldn't find a spec.

What is the correct flowrate for the in-tank pump?
Definitely sounds like a struggling main pump to me as well. Had a intermittent miss (k-jet car) that was cured by replacing the pump (less than 1 year old stock replacement) with the 740 Turbo pump. The 740 pump didn't have any polarity markings and the posts were opposite from the one I took off, so double check that crap if there's no polarity markings!

Did you use submersible fuel line and hose clamps on the pump?
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