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Long Crank on Hot Day Hot Starts

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Hi all,
My 1z is starting a little hard on hot starts on days when the ambient temp is over 85°. The car will crank for far longer (perhaps a full second) before the car starts. I have had one instance where the car cranked, started and died immediately but I believe I just didn’t crank it long enough.

Cold starts are no problem, it always starts right up. It’s not showing any codes, so I’m going to guess that it could be sensor-related... potentially on or more of three sensors. I replaced the coolant temp and the fuel temp sensor 40k ago, but I have never touched the intake air temp sensor or the MAP sensor. I have not cleaned the MAF in a while although I am not sure if it is related to cold starts.
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
No leaks at the pump that I can discern. As I mentioned it only occurs on hot days... Normal ambient temperatures result in normal starts. If the pump was losing prime overnight, for instance, I'd expect an extended crank after sitting for long stretches. I can't think of anything that would cause the pump to lose prime only on a hot day.

Granted, this is a pretty minor issue, but I tend to want to ensure that I address any looming issues before they worsen.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
Check all the temp inputs in the scan data. Fuel, air, coolant. Check the timing. If that all checks out, the pump itself may be worn internally. The start up map for cold starts is different than hot starts. Early ALHs have a sort of similar issue, and have a band aid fix with software. But I do not think the 1Z has that option.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
when things heat up, they expand, i had a serious issue when i started beefing up the performance of my ahu, the heat was causing tons of air bubbles, on cold days or cool driving, no issues. remember that a leak in your fuel lines means you get air in it, not fuel out.
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
After checking the sensor inputs on a test drive, there is nothing to suggest that any sensors are bad. They all respond as normal. My guess is that the timing has retarded a bit due to the timing belt stretching/loosening over its lifecycle (40k on it so far) which I just can't be arsed to check or adjust since I don't have VCDS and don't feel like paying the money to rent a cable right now. Injection quantity is in the range specified by DBW.

Since it rarely gets hot enough for this to occur I am going to leave it alone.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
So reguardless of timing advanced or retard, the car is fine. No need to graph timing. The ECU figures it all out. That's why there is a acceptable band window on the graph.
Just make sure your timing marks are spot on. I highly doubt it's a timing issue. Its definatly seems like a fuel issue to me. Have you confirmed you are not losing prime ?
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
So reguardless of timing advanced or retard, the car is fine. No need to graph timing. The ECU figures it all out. That's why there is a acceptable band window on the graph.
Just make sure your timing marks are spot on. I highly doubt it's a timing issue. Its definatly seems like a fuel issue to me. Have you confirmed you are not losing prime ?
Tough to test just because it hasn’t been hot out lately. The car has been starting as normal. My guess is that the hot start map is just a little off and blazing hot intake air makes it worse.
 
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