Unusual starting problem
 

Hello all. I'm interested if anybody has experienced this problem 1st hand and if so, what was the solution.

Engine starts immediately on the 1st turn when cold.

If I shut off the engine it restarts immediately.

If I drive it and bring it up to temperature and shut it down it does not start on the 1st attempt. Thereafter it might take 3-7 attempts before it will start again.

When it eventually does start it starts immediately on the 1st turn. On those attempts where it doesn't start I can crank and crank with no success.

Has anyone actually experienced anything similar to this?

If so, what was it?

Thanks!

r2

1984 300SD
232k miles

Working through exactly this kind of thing - with similar symptoms. Guys here have been very helpful...

Mine was a fuel starvation issue. Old diesel fuel/sitting for a couple of months in 30+ yr-old lines, which deserve replacement anyway... Well, you do the math!

Replacing both fuel filters has been a day and night fix, even if only a stopgap. Next steps are tank cleaning, replacement of lines, etc.

If you're burning VegOil, got a feeling you have a slew of additional variables. Experts here can help.

Pull the brown vacuum line off the shut off valve before attempting to start it the next time it's hot and see if that solves your problem.

Do you have the old style twist and pump primer pump? Sounds like a fuel issue too

Check for vacuum in the fuel tank. If you get a whoosh when you open the fuel cap, the vent system is plugged up.

This is a possibility but just leave the fuel cap off or remove it temporarily when you do not expect it to start. Do this as soon as you shut down in case suction is pulling your fuel back as the car sits making the restart hard.

If this were the case the lift pump valves may be leaky as well. They act as the return check valves in the fuel system as well as enabling the lift pump to function.

In reality there are many possibilities for your problem.

How long do you have to leave it before it will re-start first time...?

Could well be that poorly dried veggy has rotted/corroded the elements--That now wont generate the high-pressure when they are warm/hot....

OK when cold--because the fuel is a higher (cold) viscosity....

So after it warmed up I pulled the brown w/blue stripe hose from the shut off valve and bingo, it started right up! It gurgled as I removed the hose. Replaced the hose and it wouldn't start.

So does that mean replacement of the valve or could it be a vacuum issue downstream? It looks like the cost is about $165.

The problem is that vacuum is not being bled off the diaphragm. The ignition switch is supposed to bleed it off. Something is wrong with the ignition switch or the circuit. It's not a vacuum problem. It's a lack of vacuum problem.

OK, so how do I test for that?

T a vacuum gauge into that brown line and monitor the vacuum as you turn off the ignition switch. It should be at 0 with the engine running. It should rise to turn the engine off. Then when you turn the key to the start position, the switch should bleed that vacuum off to zero again.

OK, so if the vacuum is not at 0 with the engine running or the ignition in the start position and if the vacuum doesn't rise to turn the engine off then what are the possibilities? Is it that either the ignition switch is bad or there is a leak between the switch and the shut off valve?

It could be the below Valve is now no good or some how something is plugging one of the Ports inside. A new Valve used to be had for about $28.

Although it still works if when you Pulled the Hose off of the Vacuum Shutoff Valve on the Fuel Injection Pump there was Engine Oil in it the Diaphragm insde is allowing Oil to pass through it.

Some have been putting what Hunter Calls a "Hens Tooth" Fuel Filter in that line so the Oil does not make it to the Vacuum Valve on the Steering Colum Lock and mess with it.

Not sure how the ports got blocked in this case but here is a thread on that. "Turns out the ports were almost completely blocked." Post #8
http://ozbenz.net/viewtopic.php?f=5&t=17232&sid=dbda5c9d276acbb09fe894f9e1634dee

What you did when you removed the Hose was one test.

If you wanted to you could connect your Vacuum Gauge to the Hose that comes off the Vacuum Shutoff Valve. If when you turn the Key off it continues to hold vacuum you know there is a problem.

If you disconnect the other brown Hose from the main Vacuum and it still hold you know it is the Vacuum Switch on the Steering Colum Lock keeping the Vacuum From being relieved.

It is not an uncommon problem for oil to seep back into that ignition shutoff switch, causing problems...