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Thread: Bosch CIS fuel pressure gauge

  1. #1
    Senior Member Trstno1's Avatar
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    Bosch CIS fuel pressure gauge

    Ok guys-

    I just received my Bosch k-jet CIS gauge in the mail. I have it hooked up. I have read the directions but am not sure what I should be reading. What is:

    Cold pressure control: engine cold, valve open - what should it read?
    Warm control pressure: engine warm, valve open - what should it read?
    Primary pressure: venting cold or warm, valve closed: what should it read?
    Rest pressure: engine off - what should it read?

    What is the proper procedure for testing? Should I run these tests with the car running or just jumper the RPM relay?
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

  2. #2
    DMC Midwest - 815.459.6439 DMCMW Dave's Avatar
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    Quote Originally Posted by Trstno1 View Post
    Ok guys-

    What is the proper procedure for testing? Should I run these tests with the car running or just jumper the RPM relay?
    Didn't it come with an instruction sheet? Also see the service manual D:02:01 and :2. Includes charts and connection drawings.

    Car needs to be running. Except for the rest pressure test. When cold should start low and gradually rise to the operating spec, and during that rise time it should drop quickly if you spike the throttle, then become very solid. at about 3.5 Bar (see manual for exact pressures).
    Dave S
    DMC Midwest - retired but helping
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  3. #3
    Senior Member Trstno1's Avatar
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    Quote Originally Posted by DMCMW Dave View Post
    Didn't it come with an instruction sheet? Also see the service manual D:02:01 and :2. Includes charts and connection drawings.

    Car needs to be running. Except for the rest pressure test. When cold should start low and gradually rise to the operating spec, and during that rise time it should drop quickly if you spike the throttle, then become very solid. at about 3.5 Bar (see manual for exact pressures).
    Thanks as always for the reply Dave!


    I did get an instruction manual, I'm just trying to wrap my head around the tests and what they mean if the tested pressure values are different from that of the delorean technical manual specifications.


    So to test primary pressure I close the valve, jumper the RPM relay right? The technical manual says the pressure should be 4.9 bar - 5.5 bar. This test is to show fuel pressure from fuel distributer right?

    To test control pressure I open the valve, and start the engine. It should start at about 1.5 bar and stabilize at 3.5 bars or 50 psi once engine is warm right? If I blip the throttle the pressure should drop but then stabilize back up to 3.5 bar yes? This test reveals that the pressure regulator in the fuel distributer is working correctly?

    To test rest pressure I basically act like I'm testing control pressure but just shut the motor off after the control pressure has stabilized and time the pressure leakage right? The technical manual says the rest pressure should be 3.3 bars with a minimum pressure after 10 minutes of 1.7 bars. Any more loss of pressure than that proves what exactly? Either I have injectors leaking fuel after shut down or a cold start valve leaking fuel after shut down. Any thing else it could be? Bad PPR O rings? Bad check valve off of the fuel pump? Hmmm...

    Which of these tests will tell me if the WUR is functioning correctly?

    I will run all these tests in the am and report back my findings.
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

  4. #4
    Senior Member Trstno1's Avatar
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    Ok so I competed some tests this morning. Please tell me what you think.

    Primary pressure is 5 bar

    Control pressure starts at 40 psi and slowly stabilizes up to 50 psi or 3.5 bar - the blip of the throttle when cold takes the pressure down to 40 psi and it slowly increases to 50 psi again. Once the car is warm blipping the throttle does nothing to the control pressure, it stays steady at 50 psi. Am I correct in saying the WUR appears to be working, but slowly....is that normal?

    Rest pressure appears good. Its over 3 bar on shut down and only goes down to 2.6 bar after 20 minutes. -though at some point it drops to zero - not sure if this is normal or not. ( I have checked my fuel injectors and cold start valve for leaking after shutdown and they all appear to be good with no leak). Why does the pressure eventually go to 0? Shouldn't the car hold rest pressure if no leaks are present?

    Dwell reads 44 upon warm up. full throttle switch makes it go 50. once car warms up it tends to hunt a bit, anywhere from 30-45 but only sometimes. other times it stays steady at 44. Would a reading of 44 indicate a little too much fuel or not enough? either way my exhaust stinks.....

    Please check out my video and tell me what you guys think: https://www.youtube.com/watch?v=pUvvGSj1Ikk

    I am trouble shooting a cold start issue with hunting upon start and generally a lumpy idle. My fuel pressures seem to be within spec so what is the next step? testing injectors? vacuum? ignition? Ill change the spark plugs today and see if it makes any difference. Ill also pull the injectors and do a spray pattern test.
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

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    Senior Member Bitsyncmaster's Avatar
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    Your control pressure should start at a lower pressure. 20 PSI is what I've seen on a cold engine but it starts moving up pretty quickly.

    Something is wrong if your dwell is holding steady at 44 deg. on a warm engine. The warm engine should always be adjusting the dwell. Have you replaced the O2 sensor yet?

    My rest pressure will hold for about 3 hours with my RPM relay fix disabled.
    Last edited by Bitsyncmaster; 03-06-2016 at 04:44 PM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  6. #6
    Admins Never Retire Ron's Avatar
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    Quote Originally Posted by Trstno1 View Post
    I'm just trying to wrap my head around the tests...

    So to test primary pressure I close the valve, jumper the RPM relay right? The technical manual says the pressure should be 4.9 bar - 5.5 bar. This test is to show fuel pressure from fuel distributer right?
    Yes.
    This test confirms the Pump is creating enough primary pressure, the Primary Pressure Regulator (PPR) is working correctly, and that fuel is passing through that section of the FD on its way to the Control Pressure Regulator (AKA CPR, or Warm Up Regulator (WUR) ).

    Quote Originally Posted by Trstno1 View Post
    To test control pressure I open the valve, and start the engine. It should start at about 1.5 bar and stabilize at 3.5 bars or 50 psi once engine is warm right?
    Yes (...1.5 bar, IF you started the test after the engine has sat all night and was around was around 50 F. when you started).
    ***

    Quote Originally Posted by Trstno1 View Post
    If I blip the throttle the pressure should drop but then stabilize back up to 3.5 bar yes?
    Yes.

    Quote Originally Posted by Trstno1 View Post
    This test reveals that the pressure regulator in the fuel distributer is working correctly?
    No, the pressure regulator inside the Fuel Distributor (FD) is the Primary Pressure Regulator (PPR) mentioned above.

    This test reveals that the pressure from the FD, mentioned above, should reach the Control Pressure Regulator (CPR...) and that it is regulating control pressure correctly. (It is mounted on the left valve cover.)

    Quote Originally Posted by Trstno1 View Post
    To test rest pressure I basically act like I'm testing control pressure but just shut the motor off after the control pressure has stabilized and time the pressure leakage right?
    Yep, that will work.

    Quote Originally Posted by Trstno1 View Post
    The technical manual says the rest pressure should be 3.3 bars with a minimum pressure after 10 minutes of 1.7 bars. Any more loss of pressure than that proves what exactly? Either I have injectors leaking fuel after shut down or a cold start valve leaking fuel after shut down. Any thing else it could be? Bad PPR O rings? Bad check valve off of the fuel pump? Hmmm...
    This test shows if you have ANY pressure leaks. (This includes all of the places you mentioned...and more ;-)

    Quote Originally Posted by Trstno1 View Post
    Which of these tests will tell me if the WUR is functioning correctly?
    ***
    The Control Pressure test (valve open) -- Remember, the Control Pressure Regulator and Warm Up Regulator is the same part!
    Last edited by Ron; 03-06-2016 at 05:39 PM.

  7. #7
    Senior Member Trstno1's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    Your control pressure should start at a lower pressure. 20 PSI is what I've seen on a cold engine but it starts moving up pretty quickly.

    Something is wrong if your dwell is holding steady at 44 deg. on a warm engine. The warm engine should always be adjusting the dwell. Have you replaced the O2 sensor yet?

    My rest pressure will hold for about 3 hours with my RPM relay fix disabled.
    The control pressure shown in the video was a cold start. It seems as though the warm engine is adjusting dwell constantly. The O2 sensor was replaced last summer, but then again I drove the summer with the new O2 sensor with a iSM seized 3/4 closed. Maybe that's what bad. I am letting it idle now to come up to temp and see if it starts hunting.

    What would it mean if the control pressure starts so high? It seems after a cold start its immediately at 40 psi and gradually increases to a little over 50 psi before it stabilizes.

    I'll let it warm up and shoot another video of the behavior.
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

  8. #8
    Senior Member Trstno1's Avatar
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    Ok -

    I was attempting a fuel injector flow test to see the spray patterns. I also swapped the spark plugs since they have not been swapped since the engine work. Here is the video: https://www.youtube.com/watch?v=fAMB7BDaUv8

    Also....

    here is a video of the dwell hunt after the car was warmed up. Too rich, to lean? https://www.youtube.com/watch?v=7PUEhEiOOrA

    Would you let me know if you guys are getting volume with the video? They seem to play fine on my Ipad but I have not volume on the PC I just upgraded to Windows 7. Thanks!
    Last edited by Trstno1; 03-06-2016 at 06:26 PM.
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

  9. #9
    Admins Never Retire Ron's Avatar
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    RE the vid:
    IFF your plugs, timing, idle RPM, etc are correct, there are no vacuum leaks, and it is fully warm, you need to lower the dwell to swing equally above and below 40. This will take a very, very, very, little turn.

    If the control pressure doesn't recover (to ~50) after fully warm (fans have cycles a few times) and revving, you might test the delay valve (see manual).

  10. #10
    Admins Never Retire Ron's Avatar
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    After seeing latest vid: Dwell looks good now. I would double check all settings, put some new plugs (save those tho) and injector cleaner in it, then run dwell check again after running a tank full through it.

    ...the initial seeking right after a start could easily be from the leaky injector(s)...ie the extra fuel has to be burn off and not fool the O2 sensor, so to speak. Uneven injector delivery can screw that up at other times too.

    40 psi is correct if the engine sat all night at ~80 F. Once you start it. even for a few seconds, all bets are off!
    Look at it as a choke, it only matters until the engine is warm (above 104F, or 40C, and @ 50 psi, basically forget it.
    Last edited by Ron; 03-06-2016 at 06:44 PM.

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