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Cold start system problems

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Cold start system problems

Postby tonkamu » Sun Nov 26, 2017 8:33 am

I've pulled off the 2 wires off the big sensor ontop of the thermostat housing. Went for a drive and noticed loud exhaust sound when in low revs and something which sounds like a butterfly closing in the exhaust and can also hear a whining/whistle.
I'm not sure what has caused the sound but I've never experienced that noise before pulling off the wires, its if there was a switch turned on and suddenly it sounds like there's no firewall its that loud and the noise turns off after a few seconds. It sounds like if there was a hole in the exhaust its that loud.

But when on motorway or powering through a gear both noises stop then return when low revs.

Do I need to put back the sensor, is this the cold starter in the downpipe and high revs pushing it open? its friggen annoying i've never heard those sounds on my car before ever.

engine is a 4jb1-t manual 1991

I was also wondering if the early 4jb1-t engine has a different downpipe as mine goes straight down infront of oil filter or is that normal?

Seems to be a lot of room for a larger downpipe on my engine?

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tonkamu
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Re: Cold start system problems

Postby geeves » Sun Nov 26, 2017 2:49 pm

It shouldnt make that much difference but removing those wires does advance the injection timing causing diesel knock. Advanced timing is good for cold starting. Driving like this is not good for a warmed up engine. It can melt pistons and overheat. Better to put the wires back.
Then we can ask why you were playing with this in near summer conditions. The 4jb1 will start without a cold start device down to near freezing
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Cold start system problems

Postby isuzurob » Sun Nov 26, 2017 4:43 pm

The single wire sensor on top controls the flow plugs the 2 wire 1 is a waste of time never used it, but I have no vacuum controls or anything on my engines, cold start is inside the injector pumps not electronic controlled?? With the filter facing up you can just get a 2 1/2 dump pipe on but is a nightmare best to change oil filter assembly, yours looks to be factory
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Re: Cold start system problems

Postby tonkamu » Sun Nov 26, 2017 5:03 pm

How can I disable the advance timing thing? the sensor is pretty past repairing, the wires I can't even tell which one is which. Wouldn't it be advance timing continuously with out the sensor, it would always be reading 0 degrees?

I've taken off the diaphragm auto fast idler from fuel pump.
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Re: Cold start system problems

Postby geeves » Mon Nov 27, 2017 4:40 am

Much easier and probably cheaper to replace the sensor. You have lots of specialist isuzu wreckers up your way
Fast idle thing was only for air con
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Cold start system problems

Postby tonkamu » Mon Nov 27, 2017 9:11 am

yeah getting harder to find parts for the mu's now. found second hand sensor for 40 last one connection parts had in nz and CalIsuzu had no stock in nz or japan, becoming bit of a worry.
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Re: Cold start system problems

Postby tonkamu » Mon Nov 27, 2017 2:12 pm

My mechanic mate says the sensor is a breaker and the circuit is a closed loop until 5 degrees and below opening the circuit? So if I join the 2 wires on the circuit and leave the sensor unattached It should by-pass the switch and never activate the cold start/advance timing.

Does this sound right?
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Re: Cold start system problems

Postby geeves » Mon Nov 27, 2017 2:49 pm

As long as we are talking the correct sensor yes.
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Cold start system problems

Postby isuzurob » Mon Nov 27, 2017 3:54 pm

It can't advance the timing as I said before only electronics on the pump is stop solenoid, rev counter sensor, tps if you have a tps, don't need that if manual either
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Re: Cold start system problems

Postby tonkamu » Mon Nov 27, 2017 4:44 pm

Ok so any ideas what has happened? The only thing I've touched is that sensor on the thermo housing. I am now getting loud bore or similar to a hole in the exhaust sound at random times while driving on a cold and warm engine. The noise will completely stop like something has turned something off. I haven't noticed it on the motorway or in high revs.
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Re: Cold start system problems

Postby isuzurob » Mon Nov 27, 2017 5:10 pm

Weld the flap open in the dump pipe or take dump pipe off and unbolt the flap, remove all the vacuum hoses and solinoifs in the engine bay it's all junk, if you have a.c it will idle abit lower, just have 1 big vacuum hose to brake booster and small hose from turbo or pressure side of turbo to top of injector pump, noise will be back pressure in exhaust and exhaust gases are coming out intake, also remove egr valves if you still have them
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Re: Cold start system problems

Postby tonkamu » Tue Nov 28, 2017 9:49 am

Thanks yeah planning to clean up all those rubber vacuum hoses. I was looking at downpipes pretty pricey. Where do I make the weld to keep the flap open with out having to take off the downpipe as it will be a cut job its just to rusted, cant see the edges of the nut anymore. cheers
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Re: Cold start system problems

Postby tonkamu » Wed Nov 29, 2017 11:36 am

QWS.JPG


Do I pull off this assembly in the yellow circle and with the left over bolt that turns the flap do I attach it to piece of wire to hold it in one position? :oops:
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Re: Cold start system problems

Postby isuzurob » Wed Nov 29, 2017 2:42 pm

You should be able to just weld the spring and bolt both ends to the steel plates if that makes sense, looks abit yuck but worked on 1 I did
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