Hot start problem

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Kubelwagen
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Location: Portland, OR
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Hot start problem

Post by Kubelwagen » Sun Sep 01, 2013 10:47 am

This is on my "spare" engine that I currently have in the Vanagon. Van starts great when cold, even after sitting for awhile which is nice. Running great too, little tired but gets on down the road just fine. Pull in someplace and jump back in and it is a pain to start. Acts like it floods out, pumping the brake pedal to suck in some air and multiple tries and it will start, stumble for a bit (burning up excess gas?) then run fine. I let it set for a couple of hours at Hal's yesterday while we worked on his shed and it started perfectly - it seems to be entirely temp specific. Engine above X, hard start. Engine below X, perfect start.

Running errands with Hal yesterday we discussed it as I struggled to get it started. There is a checked out and per specifications AAR installed along with a brand new TS 2. Engine is tuned per Colin-visit with very few miles on it since he was here. My theory at this point is that my thermo-time switch may not be performing to spec.

Here's the oddity. I was having the exact same symptoms on my other engine. This engine has the same AFM and harness, but a different thermo-time switch and, well, everything else is different. How do I tell if the problem is the switch or the harness? What is the best way to test the switch? I have a spare switch in my box-o-stuff is there a bench test?
Patience the 81 Adventurewagen

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Amskeptic
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Re: Hot start problem

Post by Amskeptic » Sun Sep 01, 2013 9:10 pm

Kubelwagen wrote:This is on my "spare" engine that I currently have in the Vanagon. Van starts great when cold, even after sitting for awhile which is nice. Running great too, little tired but gets on down the road just fine. Pull in someplace and jump back in and it is a pain to start. Acts like it floods out, pumping the brake pedal to suck in some air and multiple tries and it will start, stumble for a bit (burning up excess gas?) then run fine. I let it set for a couple of hours at Hal's yesterday while we worked on his shed and it started perfectly - it seems to be entirely temp specific. Engine above X, hard start. Engine below X, perfect start.

Running errands with Hal yesterday we discussed it as I struggled to get it started. There is a checked out and per specifications AAR installed along with a brand new TS 2. Engine is tuned per Colin-visit with very few miles on it since he was here. My theory at this point is that my thermo-time switch may not be performing to spec.

Here's the oddity. I was having the exact same symptoms on my other engine. This engine has the same AFM and harness, but a different thermo-time switch and, well, everything else is different. How do I tell if the problem is the switch or the harness? What is the best way to test the switch? I have a spare switch in my box-o-stuff is there a bench test?
The thermo-time switch barely allows the cold start valve to work on a cold engine when the temperatures are in the 70s. When your engine is warm, it has been heat-soaked under the intake plenum, and will not activate the cold start valve at all.

Check the intake air sensor as well . . .
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Randy in Maine
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Location: Old Orchard Beach, Maine
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Re: Hot start problem

Post by Randy in Maine » Mon Sep 02, 2013 6:03 am

On a side note...

My local bus buddy was having a problem with residual fuel pressure not being maintained in the fuel rail. New fuel pump and new FPR did not help. All hoses were new and not leaking anywhere. It took a minute of cranking to get the bus to start.

It turned out that the wiring hook ups for the TTS and the AAR were switched. Once corrected, it fires right up. No more issues and it starts instantly.

Brown = TTS, Black = AAR, Blue = CSV.
79 VW Bus

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Amskeptic
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Re: Hot start problem

Post by Amskeptic » Mon Sep 02, 2013 6:33 am

Randy in Maine wrote:On a side note...

My local bus buddy was having a problem with residual fuel pressure not being maintained in the fuel rail. New fuel pump and new FPR did not help. All hoses were new and not leaking anywhere. It took a minute of cranking to get the bus to start.

It turned out that the wiring hook ups for the TTS and the AAR were switched. Once corrected, it fires right up. No more issues and it starts instantly.

Brown = TTS, Black = AAR, Blue = CSV.
If there was no residual fuel pressure, then replacement of the fuel pump and pressure regulator may have corrected that problem.

As for hard starting, yes, getting the correct plug onto the correct component can only help.

Since both the AAR and the TTS are merely heaters, what do you think the physics of the hard starting was?

Correct Wiring:
The AAR plug has a 12 volt constant supply.
The TTS has a starter-only 12 volts supply.

Incorrect Wiring:
The AAR would lose voltage the instant that the starter disengaged and
would eventually warm to open by engine heat alone.
The TTS would break its ground and be done for the rest of the day even if it did have a continual 12 volts.

When I first read this, I thought the cold start valve was draining the fuel pressure because it was getting AAR continual 12 volts, but then I remembered that the cold start ground is the TTS, and it breaks the ground very quickly under 12 volts to the heater.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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