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Well, there's that pipe/hose that goes ftom the intake balance pipe thing all the way back to the ecu? Manifold pressure sensing input to the ecu assuming your engine has it
The engine runs badly at low throttle opening. That means high vacuum.
I think I shall look at the vacuum controlled systems, that could affect engine behaviour.
I’m thinking fuel pressure regulator and ignition advance. What else do we have ?
leo,
i believe I replied early in the thread. I don’t know if your issue is similar to what I had, but I did notice similarities. I had experienced hesitation/backfiring/popping sound at low speed/low RPM. Eventually, when I was servicing the dizzy, I discovered that dizzy vacuum capsule was “dead”. I replaced it it with a new one. I also sorted out vacuum lines which appeared to be messed up since the time I purchased the car. Not sure exactly which of the two was responsible for fixing the backfiring, but when I put the car back in service, the backfiring was gone! (Knock on wood)
I have bought myself a vacuum test pump and tested everything I could find using the Focus S-58 publication as guideline.
I also checked resistance of the thermo sensors and function of the vacuum switch.
Ignition advance: No leak including connecting lines. I have not removed the distributor cover to see if it actually works yet.
ECU vacuum line: No leak, checked at the connection to the large metal balance tube
Gearbox vacuum line: No leak
Climate control: No leak
Inlket fuel pressure regulator incl line: No leak
Outlet Fuel pressure regulator: Leak at broken hose connector.
Fuel pressure thermal valve: Vacuum leak in the valve itself
Thermo sensor at LH thermostat housing: 2,640 ohm @ 15-17C. OK as 20C reading should be 2500 ohm
Thermo sensor at RH thermostat housing: 850 ohm @ 15-17C (for instrument ? )
Thermo sensor at LH air inlet: 2780 ohm @ 15-17C. Bad, as 20C reading should be 300 ohm
Vacuum switch is closed below 0.85 bar absolute pressure (0.15 bar vacuum). But: It has resistance, and the resistance is anything from 10-200 ohm. It reacts to movement of wirng, so I would say it's defective ?
I'm not sure how to check the following for correct function:
Solenoid vacuum valve placed at RH rear under the inlet manifold connected to vacuum regulator. Should I check if it opens/closed with 12V supply ?
Vacuum regulator
Dump valve
My supplementary air valve system works. Idle drops, when I turn A/C off (by choosing fan off)
I do not have air injection and therefore no thermal vacuum valve. Instead I have an extra thermo sensor at right bank rear end water line. Only 6.8 ohm measured. Any idea what this is for ? Connected to a black and a black/white wire
I'm not sure if I have the purge system, but I guess so. I spotted a grey delay valve, and I think that must be for the purge system.
So I have an engine, where the ECU thinks the inlet air is extemely cold. The fuel pressure cannot increase at high fuel temp due to vacuum leakages, but that should not be the end of the world I guess ?
The vacuum switch with resistance when open will influence at WOT, where I have no issues
BR Leo
Front end of RH inlet manifold plumming. EAC 7934 is connected to throttle housing and vacuum regulator at one port and the solenoid vacuum valve at the other port. I don't know the function to be honest. The supplementary air valve can be seen at right side of the photo.
Below RH rear end of inlet manifold
The 6.8ohm thermo sensor, solenoid vacuum valve and vacuum regulator is visible
Under RH throttle housing. A delay valve can be spotted among the tubes...
Last edited by leo_denmark; 08-25-2018 at 01:37 PM.
Reason: Typos
Acoording to sparepart lists XJ40 and XJ-S uses same air temperature sensor, and as I have both in my drive I thought I would be smart and try to mount the XJ40 sensor.
It turns out that it also has an 8-10x higher resistance compared to what I find described in the S-58. I checked with the ROM, that confirms the 300 ohm @20°C for the 5.3 l HE V12. Haynes agrees.
For the XJ40 Haynes lists values in the range I measure on both XJ40 and XJ-S V12. Around 2500 ohm
I guess 300ohm is correct and hope the EAC2863 I have ordered is 300ohm.
The informations is for sure conflicting, as even jaguarclassicparts.com lists same sensor for both engines in XJ40, XJ series 3 and XJ-S
Leo, check this link..i remember reading this a while back
Excellent, thanks!
This means all manuals are wrong and my sensor is good.
Bad news is that I now haven’t found anything seriously wrong on my car, which could affect low throttle running...
I guess I will have to start looking for loom faults. Greg has suggested ignition amp, but I find it hard to see why it should fail exclusively at low throttle/high vacuum.
The good news is that the intermittent part of this issue is more or less gone. It runs badly, when I go slow (less then 90 kmh). It runs worse than bad for 5-8 minutes when I go slow after motorway driving...
You might try plugging off the overrun valves where they connect inside the air filter housing. i ended up doing that on mine after fiddling with the spring adjustment too many times. At least it would rule them out of the equation.
You might try plugging off the overrun valves where they connect inside the air filter housing. i ended up doing that on mine after fiddling with the spring adjustment too many times. At least it would rule them out of the equation.
Not a bad idea. If one or both fails badly I will get excess air at low throttle, and that corresponds well to the sensation I have when driving.
Time to look for plugs for a test. Then they can be cancelled completely afterwards if it works.
All that radio frequency noise at the beginning makes it hard to hear anything. But when it clears up the car begins to run better.
I think you have a high voltage short. Between your plug leads or possibly rotor to dizzy shaft.
Check your plug gaps gaps are tight to .025, check for inter-plug-wire arcing in the dark, and look inside your dizzy rotor carefully for any dark spot between top of shaft and bottom interior of the rotor.
All that radio frequency noise at the beginning makes it hard to hear anything. But when it clears up the car begins to run better.
I think you have a high voltage short. Between your plug leads or possibly rotor to dizzy shaft.
Check your plug gaps gaps are tight to .25, check for inter-plug-wire arcing in the dark, and look inside your dizzy rotor carefully for any dark spot between top of shaft and bottom interior of the rotor.
Sure has something generating radio spikes.
I have removed the condensor in the ignition amp, recommended by Grant. I dont know if this gives radio noise ?
4000 km ago I changed dizzy cover and rotor (OEM parts) and mounted a set of blue Magnacor leads. I had same issues before changing these parts, just not as bad. New NGK plugs as well and gapped to 0.025".
I would expect ignition to fail at high load. High RPM and WOT must be much worse conditions.
Please try to FFW in the video to 3:00. Here I restarts the engine after it stalled, and it runs poorly without the radio noise...
I have removed the condensor in the ignition amp, recommended by Grant. I dont know if this gives radio noise ?
I don’t know either. But what I was suggesting is that every time I heard a radio spike your engine misfired. When the radio spikes cleared up your engine revved properly. There is a 1:1 relationship between the two to my ear.
Originally Posted by leo_denmark
4000 km ago I changed dizzy cover and rotor (OEM parts) and mounted a set of blue Magnacor leads. I had same issues before changing these parts, just not as bad. New NGK plugs as well and gapped to 0.025".
I would expect ignition to fail at high load. High RPM and WOT must be much worse conditions.
A reasonable expectation. For some failure modes. Not for all.
Originally Posted by leo_denmark
Please try to FFW in the video to 3:00. Here I restarts the engine after it stalled, and it runs poorly without the radio noise...
The only link I see is for a 30 second version. Can you repost the longer version link?
I don’t know either. But what I was suggesting is that every time I heard a radio spike your engine misfired. When the radio spikes cleared up your engine revved properly. There is a 1:1 relationship between the two to my ear.
A reasonable expectation. For some failure modes. Not for all.
The only link I see is for a 30 second version. Can you repost the longer version link?
The shorter version, which Youtube for some reason postponed for something like 24 hours, is just what I wanted you to hear.
I have heard the video again, and I now fully agree with you. There is for sure radio noise when the engine misfires. Important finding, thanks a lot ! I will stop chasing vacuum and fuel/air delivery !
You pointed out dizzy cover and rotor as suspects. They are not old and they look nice. Where should I look for faults ?
Greg pointed on ignition amplifier. Can it cause errors on the high tension side ??
Last edited by leo_denmark; 08-28-2018 at 01:38 AM.
Leo
I think the amplifier is more likely than the TPS. The red TPS is very reliable, and you can reliably measure its performance with a voltmeter. SO why not do that before paying for a new one.
I had a very intermittent no-start problem for quite a while and in the end a new amp fixed it. I am furthered in my belief as you had the amp open and it did have some effect, so you might have nudged some failing component into temporary action.
Manners have them, not too bad price-wise Jaguar Partno_DAC2673#_IGN.AMPLIFIER EARLY XJ12 SER3/XJS 81-84_David Manners Group with Alts
My engine is from an '89 XJ12, and I suppose my ignition amplifier must therefore be the DAC4104 rather than the DAC2673.
I think I will consult the Kirby PDF before I order, it's not exactly cheap, and Jaguar states it's NLA.
I believe I have read, that the actual amp inside the box is some cheap GM unit
The amp contains a standard HEI control module. Commonly found in the distributor of vehicles from this era. GM D1906 is a common replacement part. I’m not certain that is the proper GM part for your specific model or not. Pretty much any equivalent 4 pin HEI module works in my 86.
They usually fail under high high heat. With no spark being produced. The module is passing the trigger signal along and doesn’t otherwise get involved in the generation of the high voltage spark.
Its very unlikely any any of the other components in the amp will fail.
In the dizzy, spark can jump from the input from coil, straight through the rotor and to the shaft. It can also jump from rotor to cap between output electrodes if heavy trails of vaporized metal build up between the outputs. Then, finally, it can escape the wires and jump to the block or other wires.
Look for a small small black or brown dot inside rotor button to see if you have a short through the rotor. Look inside the cap for trails between the output electrodes. For wires, you can look for flashes of light in a very dark garage. Or flex them around by hand and see if you can induce misfiring. Sometimes you’ll get a very positive result right in the palm.
New parts are suspect as are very old originals. One for wear the other on general quality issues. NOS OEM caps and rotors are great quality but hard to find at a reasonable price.
Accessible parts cleaned and sprayed with silicon. Assembled. Runs just as good (bad) as before. Accessible means: Didn't take ignition leads A1-5-6 and B1-5-6 off to clean them...
I tried moving the wiring on high and low tension side around without any effect, but that made me think once again: The engine fails after driving a distance, during driving. It's is really hard to make at fail when stopped and especially with bonnet open. That is just plain weird...
Took a look at the engine running after a drive in the dark, and I do actually see occasional weak flashes. It's nothing like the sparks a spark plug makes, but nevertheless: Some sparks are escaping...
I then did a drive with camera strapped to the fuel rail over cylinder A3. I managed to catch really lousy running, and I do not see i single flash in the video. Maybe a cheap actioncam is not capable of filming these ultrashort flashes, but I think we can conclude it's not like a discoteque under the bonnet.
The injector solenoid noise goes mechanically in the camera, so the engine sound so sick in the video...
I promise it sounds better IRL, even when missing
When listening to the video it's my impression there are drop outs in the injector pulsing. Any thoughts ??
Leo
It has to be electrical. I would do two things:
get a known good amplifier and try it. FWIW, I changed the HEI module on an amp and my car still had intermittent no start problems. Bunged on a known good OEM amp and all good. So I do not trust just changing the HEI module.
This is a bit of work, but take a look at the pickup module in the dizzy, the thing that the start wheel runs past. It is all of a piece with the bottom moveable advance part, and has two wires that go into the bottom of the V and up to the amplifier. These just might be shorting out or even have a semi-break under the insulation.
08-24-2018, 03:13 PM
