after engine is warm it wont re start help

[1life2live]

I just finished putting together my friends 86 jetta 1.6td. We had the pump and injectors rebuilt installed a new timing belt, water pump, headgasket and did a 2 1/2" turbo back exhaust. I have all the tools to set the pump timing and did it just as the bentley says and went through the whole torque sequence on the head. The car fires up when cold and has a bit of a rough idle at first missing a little for about 10-15 sec and then smooths out and runs fine. You can drive it up the road with no issues and it acts fne but when you shut it off it usually will not restart. IF you play with the throttle while cranking it trys to start and sometimes eventually will but sometimes it wont. If it does re start it puffs a fair amount of smoke out but idles smooth and runs fine.

Any ideas as to what might be wrong im stumped??

[truckinwagen]

have you done a compression test?

this is a classic low compression symptom.

starts fine when cold(glow plugs cycle) but not when hot(glow plugs do not cycle)

you can try unplugging the glow plug temp sender so it will cycle the glow plugs regardless of engine temp(it always thins it is cold) and see if that helps.

-Owen

[rabbitman]

Did you try pulling the cold start lever? Usually that'll help in that situation. If it fixes it then just advance the timing a bit.

What did you time it to?

[damac]

I came to research the same topic.  My jetta does the same thing.  It will fire right up cold, but takes a few revolutions when warm.  This seemed odd to me but I didn't think much of it until this past week when it seemed the battery was going to go dead before it started after a quick fillup.

Looking back, my setup is laboring to turn the engine over when hot, never on a cold morning?  Is  yours doing the same thing? 

[regcheeseman]

For the OP, it sounds like the timing may be a bit out

For everyone else, disconnect the blue/white wire that goes to the temp sender.

It's a workaround/quick fix but it works.

I'm building the loom from scratch for my car and I'm not even going to include that wire.

[1life2live]

thanks for the input I really hope its not a low compression issue since the headgasket is brand new and it didnt have this issue before we swapped the headgasket. Could I have the glow plug wire in the wrong place or does that not really matter. Im guessing it doesnt matter so ill try pulling the wire off so the glow plugs will light when warm. I have a mk1 td and it cycles the plugs anytime you turn the key on im guessing it doesnt have the temp sensor wire.

As far as timing goes I have it set right on were the bentley says to put it. I cant remember what that is but I know i had to convert it from mm to inches because the gauge i have reads in inches. I thought about re checking the timing just to see if it moved.  

I just thought about something else. We had the head resurfaced to make sure it was good and flat could something have gone wrong then? There was the typical cracks between the valves but im pretty sure thats not an issue

[arb]

thanks for the input I really hope its not a low compression issue since the headgasket is brand new and it didnt have this issue before we swapped the headgasket. Could I have the glow plug wire in the wrong place or does that not really matter. Im guessing it doesnt matter so ill try pulling the wire off so the glow plugs will light when warm. I have a mk1 td and it cycles the plugs anytime you turn the key on im guessing it doesnt have the temp sensor wire.

As far as timing goes I have it set right on were the bentley says to put it. I cant remember what that is but I know i had to convert it from mm to inches because the gauge i have reads in inches. I thought about re checking the timing just to see if it moved.  

I just thought about something else. We had the head resurfaced to make sure it was good and flat could something have gone wrong then? There was the typical cracks between the valves but im pretty sure thats not an issue

And you followed the full procedure including loosening the cam bolt (some have skipped this) ? Yes, double check your math and the actual timing.

[1life2live]

I don't remember anything about loosening the cam bolt in my bentley. I was using the bentley for my 84 td but I double checked it against all data and it was the same.

I also talked to my grandfather who has been a diesel mechanic for many years and he said to make sure the injectors opening pressure isn't set to high. Does anyone know what the opening pressure is supposed to be? I could call the place that re did them and see what they set them at to make sure they did it right.

[Vincent Waldon]

Between the conversion math and the rather cryptic markings on some dial indicators it's not uncommon to not quite get it right... there are some pictures about 2/3 down this thread that show an actual inch dial indicator in use which may or may not help ya:

http://vincewaldon.com/index.php?option=com_content&task=view&id=24&Itemid=28

And yup... loosening the cam sprocket is an important part of ensuring that the crank, the pump, and the cam are in exactly the right sync.


Glow plugs are not a factor in warm starts... this really sounds like compression or timing.

[1life2live]

Between the conversion math and the rather cryptic markings on some dial indicators it's not uncommon to not quite get it right... there are some pictures about 2/3 down this thread that show an actual inch dial indicator in use which may or may not help ya:

http://vincewaldon.com/index.php?option=com_content&task=view&id=24&Itemid=28

And yup... loosening the cam sprocket is an important part of ensuring that the crank, the pump, and the cam are in exactly the right sync.


Glow plugs are not a factor in warm starts... this really sounds like compression or timing.

I used your website to make sure i had the correct timing with my inch marked gauge and it helped out a great deal. And yes it sounds like i am like many others who skipped over the loosening of the camshaft sprocket. It looks like this is not needed if everything lines up when you install the new belt and everything lined up for me but i will take it apart again for the 15th time and re check it to make sure and let everyone know what i find out

[Vincent Waldon]

Well, it's not documented the clearest in the Bentley for sure...and there are some subtle things you learn over time...so fair game to skip the odd step here and there.  ;-)

The way I explain it to people is that the timing spec is given to the thousandth of an inch... which to me is a clue that it's  (a) a precision job and (b) pretty important for the proper running of these beloved engines.

Will be interested to hear what you learn after you've checked things that 16th time... I hope it's timing and not compression that ails ya!


Vince

[1life2live]

well the timing was off between the cam and the crank. It wasnt off much, I could almost get the cam lock plate in place. I went ahead and loosened the cam sprocket and locked the am in then retightened the sprocket and the pump timing was just out of spec so i reset it and now it starts right back up after it is warmed up.

Thanks for all the input and thanks vincent for the great website that really explains everything well with good pictures.

Im just glad it wasnt low compression

[Vincent Waldon]

Im just glad it wasnt low compression

2X... thanks for taking the time to post back with the resolution.

[1life2live]

I would have never thought that the cam being off as little as it was would cause that kind of issue. I guess a valve was just slightly open causing a loss in compression when it was warm. Either way lesson learned and thanks again to everyone for the input and advice