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Generation 2 Pajero NH - NL Models 1991 - 2000

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  #1  
Old 03-02-10
BlueJ BlueJ is offline
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Default NH v6 stalling when engine bay is hot

G'day

My NH manual has a habit of stalling when the engine bay gets hot. It has been happening now and then since I got it about 12 months ago. As it is my daily driver now, I need it to be more reliable.

Sorry for the long post below, I am trying to include everything I can that describes the problem.

After climbing a hill in 4wd low (so the speed is low and load high), when coming to a halt the engine will sometimes just stop running. Sometimes the car will restart straight away, sometimes turning the key to start results in the engine cranking but not firing. Usually it will start after a few minutes wait, sometimes I need to wait as much as 10 minutes before it will start.

After a freeway run on a hot day (30C+), coming to an intersection off a freeway exit, the engine will likewise sometimes stop running. Generally it needs a couple of minutes rest before it will restart.

On a very hot day (35C+) on a freeway run, it can run very rough. The engine power cuts out for half a second or so, then comes back, then cuts out again and so on. While this is happening, the tachometer is fluctuating wildly. When cruising at 100km/h the engine speed is about 3,000rpm, but the tachometer fluctuates between 1,000rpm and 3,000rpm. Slowing down to 75km/h (reducing load) can sometimes get the engine running smoothly again but this stuffs up other road users, so I usually pull over and let the car cool down. After it restarts it will be OK again for a while. Pulling a trailer full of camping gear home from the ocean road in 38C heat, I had to stop three times to let it cool down.

Even when the engine bay is hot, the temperature gauge on the dash reads about halfway up. So the engine coolant is not too hot.

OK, this has been happening on and off for about 12 months. But now I am using it everyday, I need to find a solution before it leaves me with the bonnet up in peak hour traffic (again). Here is what I have done over the past 12 months:

1. The first few times it stalled, I opened the fuel filler cap in case it was vapour lock. It wasn't.

2. It looks like an ignition problem. When the motor is cranking but not starting, there is no spark coming out of the coil. When running rough on the freeway, the tachometer dances all over the place from 1,000rpm to 3,000rpm, but of course the engine speed isn't changing all that much as the car is in gear and moving at 100km/h or so. The tachometer works off the ignition pulses, so it looks to me like the ECU stops sending the ignition pulses or the power transistor isn't switching the coil current.

3. I replaced the original coil, power transistor, capacitor and tachometer signal filter with a unit from a wrecker. Didn't help.

3. I checked the distributor lead and cap and couldn't see any cracks or scoring.

4. I replaced the distributor lead (between the coil and distributor cap). Didn't help.

5. I checked the ECU for bad electrolytic capacitors. It had been badly repaired in the past; the two big caps had been replaced, and whoever did it lifted and broke two PCB tracks. They put solder bridges in to connect the broken tracks. I replaced all three electrolytic capacitors and re-made the solder bridges. Didn't help.

6. I dug further into the distributor. I forgot to replace the cable to the optical sensor after looking at the dizzy, and I found that with the optical sensor disconnected, the engine wouldn't fire. It seems that the ECU needs to see the crank position before it will send a pulse to the power transistor, which makes sense. Which got me thinking that the optical sensor was cutting out when the engine bay got hot. Which got me thinking, maybe the engine bay is getting too hot?

7. I tested the viscous fan clutch and could turn it easily with my little finger when the engine was hot. There wasn't much airflow from the fan. The fan clutch had little oil left in it, so I got some silicone oil and topped it up. The fan pushed more air, and the temperature gauge went down below the line during normal driving.

I was happy, I decided that the optical sensor had been getting too hot (as the fan wasn't pushing enough air to cool the engine bay), it stopped sending the crank angle position to the ECU, therefore causing the ignition to cut out.

8. A few weeks later, the fan again seemed to be pushing less air. I bought a new fan clutch and installed it yesterday. It pushed more air, and again the temperature gauge went down. Didn't help. The car stalled three times this morning in 34C heat.

The engine bay was quite hot. I took the lead from the centre of the distributor and held it close to the intake manifold while the missus cranked the engine. No spark.



So, can anyone point me in the right direction? I've already spent lots of time and a couple of hundred dollars on this problem. I'm hoping one of you gurus can give help me out with some troubleshooting tips before I shell out for a new distributor, power transistor, coil etc.

Cheers

BlueJ
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NH GLS V6 Manual. 31x10.5" muds, rear locker, bullbar, winch. Wound up torsion bars, otherwise stock.
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  #2  
Old 03-02-10
BlueJ BlueJ is offline
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Unhappy new symptoms

Not a good day for the old Pajero.

Stalled four times on an 8km drive home just now in 35C heat.

But, on the positive side there are some new symptoms:
* burnt electical component smell inside the cabin
* clicking relay sound from the left side dash area of the car when stalling, not sure if there are any relays in the ECU?
* horrible whirring noise while coasting to a stop in neutral with the clutch in

The engine check light isn't lit. I'll pull the ECU again and have a sniff around to find what has burnt out.

The engine bay is darn hot. Even the guards are noticeably hot to the touch.
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  #3  
Old 03-02-10
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schnitzel schnitzel is offline
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I'd be suspecting fuel pump as a starting point and given the temp in the engine bay would think you also have a restricted catalytic converter. Engine will get hot but it shoulldn't be excessive.
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  #4  
Old 03-02-10
chippy4x4 chippy4x4 is offline
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ditto on the pump and exhaust
A mate had a VL commodore that did similar to what you have descrbed and it was the catalytic converter was causing exsesive heat which made a sensor tell the comp to shut down. Behaved as though it was getting a vapour lock, however that is impossible with a submerged pump. Also a pump breaking down can sometimes need to be left for a period to cool down before it will deliver fuel again. Don't rule out the fact that you may have 2 non related issues that are combining to give you your problems
cheers
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  #5  
Old 03-02-10
BlueJ BlueJ is offline
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chippy4x4 wrote:
Don't rule out the fact that you may have 2 non related issues that are combining to give you your problems

Entirely possible. I'll be happy to solve one issue at a time if it means the truck behaves better than it did today.

The cat sounds solid when I tap it; this is an indication tha the honeycomb is intact? It does run OK (when it is in fact running).

To check fuel pump pressure I'll need an inline pressure gauge? It can't hurt to replace the fuel filter anyway, I have no idea when that was last done.

Looked at the ECU and it seems fine. No burnt components in there.

The engine control relay sits just above the ECU, and as I heard clicking (like a relay turning on/off) I pulled it and took a look. Inside it looks as good as it did when it left the factory. No burnt components there either.

The engine control relay switches +12V to the ignition, injectors and the fuel pump. So if the engine control relay plays up, it will take fuel and ignition out straight away.

The engine cranks with the engine control relay disconnected, but it won't start. Just like the symptoms I have been having. The only difference is that with the relay out, the engine check light isn't lit for a few seconds when the ignition is turned on.

Problem is, the engine control relay is fed direct from the battery +12V via a fusible link. Could there be an intermittent connection in the +12V feed to the engine control relay?
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  #6  
Old 04-02-10
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dank54 dank54 is offline
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Check the terminal on the coilpack...
My Nh stalled a few times, spoke to a mate who has one and he said check the coil terminal. I cleaned it, and re-tensioned the tabbs and has been fine ever since!
You mentioned your tacho fluctuated which is often related to a poor contact on the coil power circuit also.
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  #7  
Old 08-02-10
Pajina Pajina is offline
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Hi Blue J,

I had a very similar prob with the NJ... randomly would get a miss, lose power and stop or just stall. It would start, sometimes straigth away, run rough but come good, til the next time, which became more frequent. Power transistor was the prob.

Currently, ours is where we were camping on the weekend, as it happened again to the second hand replacement. This time it wouldnt start. Some checks by the local emergency rescue we had to use pointed to that, or the ECU, but the transistor is the likely suspect.
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  #8  
Old 10-02-10
BlueJ BlueJ is offline
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Default Ahhhh that's better

Had a good day today. Got home without stalling even once. Thanks all for your suggestions, I have learnt heaps about how these things work.

Monday was a nightmare. Stalled 7 (SEVEN) times in 20min on the Western Ring Road. Thankfully the paj got me through the CBD and over the Westgate bridge before it started playing up. It was about 35C at the time. Each time it restarted after a few minutes.

Quote:
Originally Posted by Pajina View Post
I had a very similar prob with the NJ... Power transistor was the prob.
Thanks for that suggestion. Yesterday I swapped out the power transistor. I took out the one I bought from the wreckers about 12 months ago, and put the original power transistor back in. I took the opportunity to clean the bottom of the transistor and the surface it mounts too - that may help with cooling the transistor.

Today it was about 32C when I started home, and about 28C when I got here. Noticeably cooler than the days it stalled repeatedly (both 35C or hotter). The truck does behave OK in cooler weather. Maybe that's why it didn't stall today, maybe not. I'm not sure if the power transistor swap did the trick, or if it was just cool enough today to avoid the problem. I'll wait for another 40C day to run on the freeway at 110km/h with the AC on full, and see what happens.

I found that my multimeter has a frequency display which I can use for diagnosis. So I have put jumper wires onto the crank angle sensor input and power transistor pulse output. If it stalls again I'll connect the multimeter up and check ECU power, crank angle sensor input and power transistor pulse output. That should tell me which component(s) is/are faulty.

Last week I checked the ECU, ECU relay and wiring harness. Everything checked out OK. When I put it all back together, the check engine light was on. It threw an engine coolant sensor code.

I checked the resistance of the engine coolant sensor and it was within spec. So I checked continuity between the sensor and the ECU, and the wiring was fine. Finally I checked the voltage on the sensor pin and found basically 0V when I should have had 2-3V.

I traced the sensor pin inside the ECU and traced it to a small PCB that stands up from the main board (see pic below).

That small PCB seems to handle the analogue sensor signals and as you can see I broke the top left corner off. This PCB has a thin plastic backing and seems quite fragile. The black rectangles are resistors (I hadn't seen this type of resistor before).

I did fix it by adding two resistors as you can see in the picture. The resistor values are wrong, so the ECU thinks the engine is hotter than it is. The cold start and cold idle aren't good, but at least the engine check light hasn't come back.
Attached Images
File Type: jpg ECU.JPG (166.8 KB, 58 views)
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  #9  
Old 19-02-10
BlueJ BlueJ is offline
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Smile Caught in the act

Another hot day in Melbourne today, and I was prepared for the car to stall.

Earlier this week I built a 'diagnostics box' with four LEDs to show ECU +12V, ECU ground, crank angle sensor signal and power transistor pulse output. If there was an electrical problem affecting the ignition, one of the lights should go out. The idea was to wait and see which light went out when the car stalled.

First I found the appropriate pins using a downloaded wiring diagram and used my multimeter to measure the voltages and frequency (for the crank angle and power transistor) of the signals. The +12V and GND just needed an LED with a current limiting resistor. The crank angle sensor signal needed to be fed into a buffer IC, smoothed by a capacitor and then connected to an LED with a dropping resistor.

I built a PCB to hold the LEDs and other components, ran the signal wires into a project box and mounted that in front of the transfer case lever. So that the signal pins wouldn't come loose too easily, I released the appropriate pins from the ECU connectors behind the passenger kickpanel, wrapped wire around them to tap the signal, and used cable ties to secure the extra wires.

With the car running normally, all four LEDs are lit. Today when the car stalled, the crank angle sensor light went out. Normally the crank angle sensor gives pulses whenever the engine is turning, even when the starter motor is operating. The ECU needs the crank angle pulses to time the ignition, so a faulty crank angle sensor kills the ignition.

I don't know yet whether the problem is with the optical sensor in the distributor, the power feed to the sensor or a fault in the wiring harness, but at least I know where to look. I suspect it is the sensor. I think I'll replace the sensor and wiring harness together and go for a run on the freeway tomorrow.
Attached Images
File Type: jpg ECU connector small.JPG (184.8 KB, 34 views)
File Type: jpg PCB small.jpg (82.4 KB, 34 views)
File Type: jpg Diagnostics small.jpg (56.1 KB, 40 views)
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  #10  
Old 20-02-10
gaz1 gaz1 is offline
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great detective work, BJ......here's hoping you've solved it. Is the only crank angle sensor in the NH in the distributor? The later V6s with the three coil packs have it down near the front crankshaft pulley inside the belt cover.

Gaz
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Previously 02 NM auto V6 Exceed silver. Extra transmission cooler & transmission temp gauge, activated rear lights, Impco sequential LPG system, Redback (Wildcat) Headers, heavy duty radiator. Lovells shocks F & R, Polyair bags in rear.

My original Pajero experience - '90 NG Superwagon, 3.0 V6 manual bought new and kept until 1998. Great vehicle, no problems apart from the noisy valve lifters typical of that engine.
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