Fluctuating Idle RPM -Diesel P38

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kapilamuni

Active Member
Posts
550
Hi,
About a month ago I replaced the timing chains & head gasket, sump gasket etc but did not set static timing, properly. This Monday I adjusted static timing using Nanocom and set the Timing modulation to about 52 (idle , hot engine). Though it did not solve the hot start issue I had, after running for a day or two , checked the modulation again. It's floating from 48 to 93 and mostly remains at 93. Now I have a random, idle RPM fluctuating from 650 to 850/900 range with engine/car shaking badly. If I put gear to D or R it remains at 750 without any shaking. Since hot start is back, I am scared that the engine will shut in the traffic and to avoid such scenario , adjusted the idle value from 128 to 129. It did not stop fluctuations in idle RPM. Otherwise, the car seems much better.
Thanks in advance for your ideas , guys.
 
kapilamuni said:
Only one.
'injector timing value out of expected'.
Click to expand...

You MUST set the static timing mechanically with a DTI. Only once that is done can you look for problems. You can only set it using Nanocom when you are certain there are no other problems. Obviously there are. Are you absolutely certain that when you replaced the injection pump the woodruff key was not lost. Sounds as though the injection pump is moving. Where is the pump in relation to the bolt positions on the slots? When you time pump last movement MUST always be towards engine to take up mechanical slack in internals.
 
I'm sure that wood-ruff key was in place as I never took the inj pump out. Now the pump is pushed more towards the engine, by looking at the bolt positions. From a middle position , say about 60% towards engine.
In tank pump checked and output is okay. But I don't think it's the intank pump. About 3 yrs ago I ran the car with a non working intank pump and only issues were more cranking needed in starting and going above 80KPH.
Can it be the throttle position sensor, playing up within idle range? or the pump electronics as the problem is random and felt even coasting in gear.
 
Grrrrrr said:
+1 on setting static properly. After that I'd check flow from in-tank pump.
Click to expand...

Engine should run reasonably well even if intank pump is duff
kapilamuni said:
I'm sure that wood-ruff key was in place as I never took the inj pump out. Now the pump is pushed more towards the engine, by looking at the bolt positions. From a middle position , say about 60% towards engine.
In tank pump checked and output is okay. But I don't think it's the intank pump. About 3 yrs ago I ran the car with a non working intank pump and only issues were more cranking needed in starting and going above 80KPH.
Can it be the throttle position sensor, playing up within idle range? or the pump electronics as the problem is random and felt even coasting in gear.
Click to expand...

Have you or anyone else ever had the top half of the injection pump off? There is an idle switch that is supposed to engage when throttle pot is at less than 9%. Idle is then controlled by the ECU via quantity servo referencing speed signals from CPS. Check the linearity of the throttle pot and function with Nanocom.
 
Yes, I did replace pump seals/o-rings but that was about 2 yrs ago. Thereafter, it ran perfectly.
This was a very recent development. How am I to check the ,linearity of throttle. pls explain.
 
Manage to set the static timing with dial gauge. It was 0.91mm and I set it to 0.98mm.(slightly above the standard setting of 0.95mm). But the random fluctuations at idle remains together with the hot start issue. Is it the pump internals? No faults except that 'injection timing value out of expected'.
At same time, the starter motor play half dead when hot and I need to wait more than 1 1/2 hrs to get it started. May be the starter motor brushes need replacing.
For the first time during my ownership, the engine cut suddenly when reversing out of a parking lot. Waited till it got cooled down and the car started promptly. Is this event a signal on pending serious problems?
While searching the web I found this
http://www.patrol4x4.com/forum/niss...bo-diesel-hot-start-issue-fix-6428/#post39975
They talk about a worn pump and the remedy is to replace one of the covers (diamond shape) on the timing advance unit. May be our diesel experts can explain.
 
kapilamuni said:
Manage to set the static timing with dial gauge. It was 0.91mm and I set it to 0.98mm.(slightly above the standard setting of 0.95mm). But the random fluctuations at idle remains together with the hot start issue. Is it the pump internals? No faults except that 'injection timing value out of expected'.
At same time, the starter motor play half dead when hot and I need to wait more than 1 1/2 hrs to get it started. May be the starter motor brushes need replacing.
For the first time during my ownership, the engine cut suddenly when reversing out of a parking lot. Waited till it got cooled down and the car started promptly. Is this event a signal on pending serious problems?
While searching the web I found this
http://www.patrol4x4.com/forum/niss...bo-diesel-hot-start-issue-fix-6428/#post39975
They talk about a worn pump and the remedy is to replace one of the covers (diamond shape) on the timing advance unit. May be our diesel experts can explain.
Click to expand...

Sounds like the timing solenoid is failing or has failed. What is the modulation? If the mid section has been off the pump it is possibly not back in the correct position. Pump possibly needs to be tested and calibrated
 
Modulation is between 40 and 93 , mostly at 93.
Shouldn't there be a fault recorded for the timing solenoid?
 
kapilamuni said:
Modulation is between 40 and 93 , mostly at 93.
Shouldn't there be a fault recorded for the timing solenoid?
Click to expand...

You may have a bigger problem. With static set at .95 mm, if it has been done correctly, it should not be possible to get 93% modulation. 93% modulation means the timing solenoid is correcting a retarded static setting. Static setting is slightly advanced as set. Injection point slightly before TDC. When the engine starts the number four injector sends a signal back to the ECU telling it the actual point of injection. The ECU compares this to signals from the crank position sensor and modulates the timing solenoid to increase or decrease internal fuel pressure on the timing device in the pump to take point of injection to TDC at idle engine hot. Modulation at that time should be between 45% and 55%. Ideally 50%. Modulation is taken at idle RPM engine hot. NOT at other engine speeds. If you are not getting any other faults and Mill lamp does not flash on at any time i would suggest the injection pump needs to be tested and calibrated.
 
Make timing solenoid test(EDC - Outputs) with nanocom with engine running at idle speed.
Engine should change noise from very silent to very clattery a few times(it's 30 seconds test).
It it doesn't change note, or it's silent clatter, then timing solenoid doesn't work properly or internal pressure pump lacks pressure to change timing. Anyway injection pump will need overhauling or replacing.
It's also possible that number four injector is faulty giving false readings.

Edit:
Also fuel quantity set to too low value at hot engine idle speed will cause RPM fluctations, as desired fueling cannot be obtained, and ECU tries to solve the problem by cutting fuel.
 
Last edited:
It appears that I'm heading for deep trouble.
Will try N2O 's idea and see.For the timing solenoid also, should not there be a fault logged , if it's faulty?

I have already adjusted the idle value to 130 now to avoid engine stalling suddenly on the road (though happened only once, that's the worst thing with hot start issue). Now idle RPM is at around 850. How can I set the fuel quantity & what is the standard setting for that?
Also, could it be something like 'weak/ broken spring' in the advance unit ?
 
kapilamuni said:
It appears that I'm heading for deep trouble.
Will try N2O 's idea and see.For the timing solenoid also, should not there be a fault logged , if it's faulty?

I have already adjusted the idle value to 130 now to avoid engine stalling suddenly on the road (though happened only once, that's the worst thing with hot start issue). Now idle RPM is at around 850. How can I set the fuel quantity & what is the standard setting for that?
Also, could it be something like 'weak/ broken spring' in the advance unit ?
Click to expand...

The timing solenoid test is done with engine stopped you should hear it buzzing if operative. Fuel quantity at idle is changed by increasing or decreasing idle fuel value. Should be 128 to give 750 RPM. There is a fault logged but you seem to be ignoring it. As said before if you have had the pump apart and not set the mid section correctly you will get what you have reference idling. Remove pump and have it tested and calibrated. Are you still running without a stop solenoid? If you are fit one or you may regret it. You need to be addressing the 93% modulation at idle with static set at .95 that should not be happening.
 
" .................As said before if you have had the pump apart and not set the mid section correctly you will get what you have reference idling. ................"
Well, I had a leaking pump & replaced all the rubber seals. Afterwards car ran fine for about 12000KMs. Present issues came up after changing the timing chains to cure the hot start problem, in December last year.

"............Remove pump and have it tested and calibrated."........
I doubt whether it's possible here.

"Are you still running without a stop solenoid? If you are fit one or you may regret it."
Yes & definitely will fit one,waiting for delivery from UK.

"You need to be addressing the 93% modulation at idle with static set at .95 that should not be happening."...........
That's the problem. I will check the timing solenoid tomorrow.
If it's not functioning, how can the engine start when cold? Is the spring inside pushes it to fully advanced position when cold?
 
kapilamuni said:
" .................As said before if you have had the pump apart and not set the mid section correctly you will get what you have reference idling. ................"
Well, I had a leaking pump & replaced all the rubber seals. Afterwards car ran fine for about 12000KMs. Present issues came up after changing the timing chains to cure the hot start problem, in December last year.

"............Remove pump and have it tested and calibrated."........
I doubt whether it's possible here.

"Are you still running without a stop solenoid? If you are fit one or you may regret it."
Yes & definitely will fit one,waiting for delivery from UK.

"You need to be addressing the 93% modulation at idle with static set at .95 that should not be happening."...........
That's the problem. I will check the timing solenoid tomorrow.
If it's not functioning, how can the engine start when cold? Is the spring inside pushes it to fully advanced position when cold?
Click to expand...

With engine stopped there is no internal pressure within the pump for the timing solenoid to control. Car always starts from cold without internal pressure other than the small amount supplied by the lift pump, at which time the timing device has returned under spring pressure to the advanced static timing position. Only when internal pressure is made by internal pump can timing solenoid modulate pressure to apply opposite pressure against the return spring to adjust point of injection.Timing Modulation should only be read at idle speed (750 RPM plus or minus 50 RPM) with a hot engine and NOT at any other engine speed. If you removed centre section of pump and slapped it back on with no need for initial idle fuel quantity adjustment you have been a very lucky lad indeed.
 
My experience tells me that timing modulation at idle is very close(within 10%) to modulation at higher constant speed, even when driving on flat road - tested it on 3 vehicles with different timing modulation.
Try to set quatninity on HOT(no load and AC OFF) engine(middle of the guage - at least 88 deg on nanocom) to something around 5 mg/str if you can't get it calibrated. It will properly if pump is in good order and no one messed with arm position under top cover. And of course timing has to be set right.
 
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