AHU will not start

clyde

Veteran Member
Joined
Apr 8, 2000
Location
confluence, Snake/Clearwater
TDI
1998 Jetta, 1959 DeSoto with leopard-skin seat covers
1998 TDI, replacement factory motor with about 140 k miles. Been running fine for 7+ years, through last evening.

First thing this am, turned the key—it started instantly, which is what it does regularly in warm weather. Just as instantly as it started it stopped, and would not start. Decided no use in flogging it; I didn't have any test equipment with me, 90 miles from home. Took bus to get home.

Just checked the FAQ's b.1(b) - Engine cranks but does not start.
Electrical—check that ECU is receiving power MUST DO
weak bat? NO, it cranks vigorously
corroded connections @ bat—NO
weak starter—NO
fuel—half tank of good stuff
wrong injection timing—ran fine last night, and nothing has changed
anti-shudder valve not opening—DON'T KNOW ABOUT THIS ONE

Have been thinking about the fuel-shutoff valve. If this valve fails, might it not cause the symptoms I experienced? Start immediately with the fuel in the lines, then stall immediately when the lines are out of fuel?
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
I would check the codes, timing belt, connections to the injection pump and relay 109. If all are good, I would suspect the ignition switch.
 

burpod

teh stallionz!!1
Joined
Nov 27, 2004
Location
cape cod, ma
TDI
82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
i believe if 109 is bad (ecu not getting power), you won't see the CEL and glow plug indicator lights turn on when you turn the key. if they do, 109 should be good. check for 12v on fuel shutoff solenoid. i found that in my 98 tdi, if you disconnect and then reconnect battery, it gives 12v to the shutoff solenoid for a good 20-30 seconds after reconnecting the battery. i realized this because i added a lift pump, and when reconnecting the battery, it would run the pump! that makes it easy to check with multimeter rather than scrambling or using long wire leads while you futz with the ignition.

i can't remember how they were stock, but i didn't think the AHU/1z had anti-shudder valves to worry about
 

clyde

Veteran Member
Joined
Apr 8, 2000
Location
confluence, Snake/Clearwater
TDI
1998 Jetta, 1959 DeSoto with leopard-skin seat covers
I would check the codes, timing belt, connections to the injection pump and relay 109. If all are good, I would suspect the ignition switch.
Do you mean error codes? Will VAG-COM check error codes on an engine that won't start and is cold?
 
Last edited:

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
No ASV on an AHU.

Check the wires to the IP, they’re known for chafing. Specifically the black/white wire.
I'd be sure and check the wire to the fuel solenoid, a start and then immediate stop might be broken connection to that.

It's odd to get a start followed by immediate stop without some sputtering etc. It doesn't sound like the pump ran dry just that fuel was turned off.

Also, how many keys are on your key ring and when was the last time you replaced your ignition switch?

Steve
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
Bad switch failure mode is almost always a "no crank".
Do you have access to a 17mm wrench and an assistant? Crack one of the injector nuts off and see if you get fuel while cranking and report back.

Alternatively, does the tailpipe smell like fuel while cranking?
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
Bad switch failure mode is almost always a "no crank".
Do you have access to a 17mm wrench and an assistant? Crack one of the injector nuts off and see if you get fuel while cranking and report back.

Alternatively, does the tailpipe smell like fuel while cranking?
I've seen crank no start situations with bad ignition switch...

Steve
 

clyde

Veteran Member
Joined
Apr 8, 2000
Location
confluence, Snake/Clearwater
TDI
1998 Jetta, 1959 DeSoto with leopard-skin seat covers
As it's 92 miles away, I'll advance on it tomorrow with ignition switch and an arsenal of tools and check:
1. the wires to the I-pump, esp. the black-white;
2. when cranked, fuel from barely loosened injection pipe;
3. the fuel-shutoff solenoid; and
4. anything else that seeems reasonable.

Thanks for the tips!
 

jhax

Veteran Member
Joined
Jan 24, 2012
Location
Golden, CO
TDI
96 Passat B4V, ALH engine out of a 2002 Jetta, some IE Rods and ASV Pistons. Nothing drivable yet though
If you turn to ign on position and the needles on the gauges dont flick slightly, its 109
 

clyde

Veteran Member
Joined
Apr 8, 2000
Location
confluence, Snake/Clearwater
TDI
1998 Jetta, 1959 DeSoto with leopard-skin seat covers
Applied +12 to shutoff valve; it clicked lika a good valve.
Turned ignition on, Glow Plug & CEL lights came on.
Looked for chafed black-white, or any other, wlres. There were none.
Replaced relay 109—engine started. It was uncertain and weak until it received fuel without bubbles. Drove it back, 92+ miles. Seems good.
Why do bubbles appear in the fuel line? Tank was more than half full…
Is a "lift pump" worth having on this vehicle?
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Bubbles in the fuel line indicate some sort of loose connection or air entering the fuel system. This could be a chafed hose, residual air in the fuel filter, etc. The thermostatic coupling atop the fuel filter can be a source of leaks.

Either way, sounds like you found your issue.
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
Applied +12 to shutoff valve; it clicked lika a good valve.
Turned ignition on, Glow Plug & CEL lights came on.
Looked for chafed black-white, or any other, wlres. There were none.
Replaced relay 109—engine started. It was uncertain and weak until it received fuel without bubbles. Drove it back, 92+ miles. Seems good.
Why do bubbles appear in the fuel line? Tank was more than half full…
Is a "lift pump" worth having on this vehicle?
It's likely an unseated connection at the fuel filter on any of the connections or maybe more than one. If you can switch to the solid FI clamps that apply evenly over the circumference of the hose vs the gear driven clamps.

Glad to hear that you were able to get it home.

Steve
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4, '97 Jetta
Did you try to start it, prior to replacing the relay? As mentioned, the GP and CEL shouldn’t light, if the relay were bad. Curious if the relay was flaky, and occasionally not closing, when it should.

-Todd
 
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