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VW B5 Passat TDIs This is a general discussion about B5 Passat(>98 (2004-2005 in North America)). Non TDI related postings will be moved or removed.

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Old July 11th, 2018, 19:59   #1
sgriff144
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Default B5 Hard Warm Start

I know this is a topic that has been discussed on here before, but still having an issue troubleshooting.

Other week with car up to temp and low on fuel (less than 1/8 tank), I stopped to fill up at reputable diesel station. Car started routine after filling and went to hardware store 5 miles away. Approx 20 mins later I come out and car would crank, but not start/attempt to fire.

Got ride home and came on here to look at possible causes. Went back to store, took apart intake to ensure ASV was not closed, it was not the foreseeable issue. Attempted to crank car again for lack of better things to do and it started.

So...car starts fine when cold. Will start after warm if only sitting short period. Greater than approx 20 minutes will crank for extended period. Car will start with starting fluid, I do realize this is not advised. No codes on OBD2 and my vagcom is out on loan. I have replaced coolant sensor as I read this might be an issue with warm starts, still not improved. I clamped hoses on both sides of the check valve on fuel filter and thought warm starts were better. However, I replaced the valve with one from ID parts and I am still having issues. Also replaced the fuel filter. I have also read about crankshaft sensor being a cause for hard starts, but my tach needle raises off zero when cranking engine.

Seems like it is obviously a fuel delivery problem (car starts with ether) I can't help but wondering if I ended up with bad fuel or complications from fuel level being much lower than I normally let it fall before filling up. Fuel pump seems to be audible from the back when turning the key to "on."
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Old July 11th, 2018, 20:07   #2
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Fuel pump relay on its way out maybe? Do you hear the fuel pump cycle on with the key?
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Old July 12th, 2018, 03:40   #3
sgriff144
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John, I believe so. You're referring to the motor like humming noise coming from behind the right rear seat? I'll investigate it more this evening.

I should clarify that I meant "warm" start is when the engine temp is to 190.

In the event the fuel pump or relay is bad, would the car start fine with the engine at ambient temperature and not at 190? Thanks.
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Old July 12th, 2018, 07:03   #4
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As above, sounds like fuel delivery.

The usual suspects are the in-tank pump, tandem pump, or air leaks somewhere (possibly the thermostatic T at the fuel filter).

You mention that the fuel was low. If you fill the tank, does it start reliably when hot?

If that's the case, then the transfer pump in the tank is the most likely cause.
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Old July 12th, 2018, 09:35   #5
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Quote:
Originally Posted by sgriff144 View Post
John, I believe so. You're referring to the motor like humming noise coming from behind the right rear seat? I'll investigate it more this evening.
I should clarify that I meant "warm" start is when the engine temp is to 190.
In the event the fuel pump or relay is bad, would the car start fine with the engine at ambient temperature and not at 190? Thanks.
I agree it shouldn't make a difference, just throwing it out there. Anyway since you hear the hum, it should be fine. Time to check you pumps.
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Old July 12th, 2018, 09:47   #6
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I had an issue with an intermittent warm start issue. Turned out to be a 219 relay in the ecu box going. When id try to restart, key in the on position, the check engine light should come on. This is the key in on position, not starting key all the way turned position. The cel would not light. The fuel pump would not turn on. The car would turn over but not start.

I got lucky, pulled the ecu cover. Took out the relay and smacked it upside down against the side walk. Been doing fine since(early June) but grabbed a spare to keep in the dash next to a 1/4 inch wratchet with 8mm socket/6 inch extension in case it finally goes.
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Old July 12th, 2018, 16:10   #7
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Almost all TDI engines will have problems starting if the cranking RPM is not above 250. This is more likely to occur when the engine/starter are heat soaked. Its a function of the starting maps in the ECU. When cold, fuel is injected right from 0rpm. When hot, for emissions reasons, fuel is only injected above 250rpm. Check battery connections, boost the car from a second battery when the problem occurs, if it starts with a boost it may just be a weak battery. Often the starter gets weak with old age as well.

Unplugging the coolant temp sensor when hot will confirm the problem, as the ECU will default to the "cold" map, though this isn't easy to do on a B5.

If you have VCDS check torsion value as well. severely retarded cam timing can cause difficult hot starts.
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Old July 12th, 2018, 16:23   #8
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Yup had the same issue had to move the cam ahead a couple degrees and runs perfect ever since !
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Old July 12th, 2018, 19:46   #9
sgriff144
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Ive also read about timing be a potential issue...but would this be an immediate onset? I was driving the car daily and never had any issues with hesitation on starting, then all of a sudden it wouldn't start when up to temp.

I removed the cover in the trunk for the tank pump and it is definitely audible when turning the key to 'on." The car seems to crank strong. Would a failing tandem pump cause the fuel lines to lose their "prime" when warm?

The only other information about issues with the car...the car had been having intermittent hesitations when under load (pulling hills in 5th gear) Kind of like a shudder that fuel delivery might be an issue. Never thought much about it until now...
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Old July 13th, 2018, 04:24   #10
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As the timing belt stretches the t.v. changes. It could gradually happen. Especially with the onset of summer.

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Old July 13th, 2018, 07:07   #11
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If the timing is off, and the cause of the no-hot-start, then the tailpipe should smell like diesel after all that cranking (assuming fuel is making into the engine).
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Old July 13th, 2018, 08:10   #12
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Quote:
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If the timing is off, and the cause of the no-hot-start, then the tailpipe should smell like diesel after all that cranking (assuming fuel is making into the engine).
The problem with late cam timing is that the injector cam is not positioned to develop adequate pressure when the ECU requests the injector to fire. This is particularly bad at hot startup, when fuel viscosity is low, internal injector leakage is high and injector plunger velocity is low.
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Old July 16th, 2018, 08:30   #13
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Made an appointment to have the timing checked this week as that is out of my league. Thanks for the input
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