1995 Toyota 4runner hard starting when cold

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Tomblueprintauto
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1995 Toyota 4runner hard starting when cold

Post by Tomblueprintauto »

Could I please get an opinion on this cranking relative compression test? It's an old diesel so injection trigger available to isolate specific cylinders

This vehicle takes a long time to fire up when cold. The glow plugs have been replaced and are drawing 60A

You can see that the current from the batteries drops from about 400A to about 80ish every 130ms. Does this look like a bad starter motor? A few open circuit windings maybe? The starter sounds great. Doesn't sound obviously slow or anything.

EDIT: The close up screen shot shows the commutator activity. From my inexperienced eye this looks OK. Its like the load on the starter just drops away every now and again. I'm starting to wonder if its a slipping starter clutch.

Thanks
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Fat Freddy
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Re: 1995 Toyota 4runner hard starting when cold

Post by Fat Freddy »

I'll assume 'cold' means sitting a while?

Have you checked for air bleeding into fuel line (clamps, split/hard hose, etc) allowing fuel to drain back to tank? Common as hell

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Fat Freddy
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Re: 1995 Toyota 4runner hard starting when cold

Post by Fat Freddy »

I should of added ,I'll use a piece of clear hose with a twisted loop (loop to the top to check for air) in it where the line goes into the pump to confirm.

ben.martins
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Re: 1995 Toyota 4runner hard starting when cold

Post by ben.martins »

Hi Tom,

Couple of things from the this capture as this type of vehicle, there isn't much that is required to get it to run.

Cranking speed is definitely something that we need to check. Is there any way you can get the fie uploaded? Your sample rate is pretty high for something like a relative compression test which will make your file size really large. As mentioned in your other post you can select the current waveform which will help reduce the file size - viewtopic.php?p=103478#p103478.

To measure the cranking speed look at the peaks in the current and draw out a time ruler from the bottom right hand side of the time axis. You will be able to place this cursor at one of the current peaks. Grab the second time cursor and place on the peak that marks out 360 degrees as this will give you the cranking speed. If it's a 4 cylinder which from memory I think it would be, then you'll place the second time cursor on the 3rd peak.
cranking speed.png
Whilst checking for air bubbles in the fuel is always a good idea as Freddy has pointed out, you should also consider fuel flow. Just because there is fuel there might not be adequate fuel flow. No real way of testing this unless you have a fuel flow meter. One way to ensure you have a good supply is to run an independent fuel supply with known good pipework.

Fuel blockages might also not show up with clear pipework. A WPS500 in between the fuel filter and the fuel pump can show you the effectiveness of the lift pump. You should a vacuum being pulled but it shouldn't be excessive. What's excessive is a good questions! Unless we have a known good then comparing with existing signals is all we can do. We do have a guided test for this measurement which can be seen in PS7 under Pressure transducers > WPS500X > Negative priming fuel pressure (diesel). From the test we have approx. -150mbar when the engine is at idle. Should this deviate massively from this then we may have a blockage.

Compression overall looks pretty good with a current draw of around 350A, the drops in current are more typical of a starter motor commutator issue but if may not be related if your starter motor is cranking over OK.

I think if we can establish fuel supply and quality then it'll be another part of the puzzle.

Kind regards

Ben

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