1.5D will push start but not with starter.

[vdubspeed]

Swapped an old diesel into my GTI.

Compression isn't the best but runs great when it runs. I wired up a relay for the g-plugs and usually had to hold then button for like 10secs when it was cold for it to fire.  Instant hot restarts weren't a problem but 5 minutes + posed a problem. Well the other day I ran up to Advance to get a part and when I came back out...no worky worky.

The battery/starter and strong. Alternator is charging.

Pops right off when pushed and put in 3rd gear.

When I start with the key it seems like it's just about to start but won't catch.

My one question. Does this sound like a low compression issue or glow-plug issue. Once its running it's great and will run/idle for days. Drives around no problems and gets about 40-45mpg.

[jack's lack]

Did you use a diesel starter when you did the swap? I ask because they are faster and stronger than the gasser starter, and that would certainly cause the cold start trouble you are having. Are you using the cold start timing advance? That should help you out too. Are you using slow glow or fast glow GP's? Fast glow usually take about 8 seconds, but the slow glow take a bit longer.

That's all that comes to mind right now.

Cheers

[Baron VonZeppelin]

That is true, a diesel starter is about 1.5" longer than a gasser.
And the power is 1.7 kw/hp vs 1.0 kw/hp

Its not totally clear, but it sounds like maybe it is fine on cold starts, okay on immediate hot restarts, but no-go on hot restarts after sitting just a while - or longer.

Probably a heat sinking / voltage drop problem.
Is it Mk1 or Mk2 ? The later Mk2 has more problem with the battery ground location. Check both your cables for resistance, and clean all connections.

After that, if no better, you'd need to do a voltage drop test.
You can use the search function "voltage drop test" and find a write up done by Burn Your Money.

You could also have a starter that is on its way out, slowly dying from within.

Low compression is usually a bigger factor on cold starts.

I had one do like you are experiencing.
I could run the glowplugs for about 8-10 seconds on a hot restart and it would crank. Otherwise either had to let engine cool down, or roll crank it. But firing the glowplugs was a good working band-aid.

[vdubspeed]

mk1
diesel starter
I believe the plugs are slow. I know the car was parked in 1992 before I swapped it in. So it sat for 18 years:)
oh yeah...not using the cold start advance at all. don't have it hooked up.
my grounds are awesome. I overgrounded the thing really. voltage drop is not an issue.

[Vincent Waldon]

You can certainly check your glow plugs for current draw, but given the symptoms and the age of the engine 90% chance it's a compression issue.

Compression test will tell the tale... probably a good next step if only to give you an idea of when to start budgeting for a rebuild or replacement.  It might also give you a bit of warning in terms of an impending run-away.

[burn_your_money]

Do a voltage drop test. It would be important to do this before doing a compression test

[westcoaster]

Do a voltage drop test. It would be important to do this before doing a compression test

Specially considering it "pops right off when pushed and put in third gear"

This tells me the starter is sucking too much voltage away from the fuel solenoid...

[Vincent Waldon]

Or... it's able to generate enough heat at 1000 RPM that it can start... unlike the heat it sees at 300 RPM...    

Voltage drop test is a great idea... and easier to do than a compression test... so a great place to start.

[kingler5]

Do a voltage drop test. It would be important to do this before doing a compression test

Specially considering it "pops right off when pushed and put in third gear"

This tells me the starter is sucking too much voltage away from the fuel solenoid...

Can you elaborate on this starter sucking voltage from the solenoid scenario? I think I may be currently experiencing a similar problem!

[theman53]

I had a good starter but didn't replace the bushing in the trans and it wouldn't turn fast enough to start it. Roll it 2 feet down a hill and let the clutch out in any gear and it would rip. I had worn the starter out by the time I replaced that bushing 

[BAM]

Here is another scenario, assuming we have no voltage drops on the pos or gnd side of the circuits required to start the car, the engine is not beat and the correct starter for the application.  Many years ago, MK1 and MK2 cars had huge issues with ignition switches dropping the 15 circuit when in the start position and the fuel shut off solenoid would NOT get the required voltage allow fuel to flow. Just throwing it out there for consideration and reference.

[theman53]

Here is another scenario, assuming we have no voltage drops on the pos or gnd side of the circuits required to start the car, the engine is not beat and the correct starter for the application.  Many years ago, MK1 and MK2 cars had huge issues with ignition switches dropping the 15 circuit when in the start position and the fuel shut off solenoid would NOT get the required voltage allow fuel to flow. Just throwing it out there for consideration and reference.

Maybe try running a jumper from the battery just to eliminate that possibility?

[vdubspeed]

I'll screw with it some more tomorrow.

Yesterday though I charged the battery, warmed up the plugs for 15secs and used the cold start advance...it fired almost immediately.

That to me almost wipes out compression.

I'll check:
starter bushing
voltage drop
solenoid power

I'll probably through in some fast glow plugs anyway. I want some new ones to ensure they all are working plus I hate waiting so long for them to warm up.

Thanks all,

Jason

[kingler5]

Here is another scenario, assuming we have no voltage drops on the pos or gnd side of the circuits required to start the car, the engine is not beat and the correct starter for the application.  Many years ago, MK1 and MK2 cars had huge issues with ignition switches dropping the 15 circuit when in the start position and the fuel shut off solenoid would NOT get the required voltage allow fuel to flow. Just throwing it out there for consideration and reference.

THIS!!! Where can I get more info on this?

[RabbitJockey]

when i had a few bad slow glow plugs, i couldn't find new slow plugs, so i just replaced the replace and all 4 plugs with cheap stuff, i did it for around 50 bucks... but i know you don't have a timer relay.  slow plugs are slow too, 10 15 seconds is actually how long they are on, also on a real diesel setup the glow plugs actually stay on until you turn the key, or after 20-30seconds they turn off you can here it click.  so just cause the lights off on a normal car doesnt mean the plugs are