1972 280SE 4.5 flooding at start up

[billhard]

Hello all, l am hoping for some of your thoughts about why my Jetronic system is flooding the car at start up. Here is what I have observed:

1. The car floods itself at start so badly it won't run. This is to the point I was worried about hydrolock.
2. If the fuel pump is disconnected the car will start, race some as it burns off fuel and then of course dies when the fuel supply runs out.
3. Fuel pressure is at 30PSI
4. I was able to get the engine running long enough to check vacuum at MAP and it was 10 inches.
5. Then I started looking for vacuum leaks. Plugged the lines leading to the cabin, no change. No audible leak in the brake system can be heard.
6. Then I noticed the PCV valve was not opening. With some TLC and a lot of Sea Foam the valve came back to life. Now the engine was producing 15 inches of vacuum at idle and running pretty well.
7. I don't think that is the main issue though and here is why. When you put the breather hose back on the PCV valve and breather the car again stubbles and begins to over fuel.

My understanding is that low vacuum is telling MAP that throttle is being opened and it is responding by increasing fuel flows. I have always thought low crankcase venting was a good sign, perhaps there could be some other reason for vacuum loss? What are your thoughts?

[cth350]

does the system maintain that 32psi when you turn the fuel pump off?
If it drops immediately back down towards zero, that pressure is leaking off somewhere.

How old is the line from the manifold to the MAP? If you don't know, then it's too old. It needs to be a strong enough line to not collapse and the ends should be clamped.

You can use a duty cycle meter on the injectors to see what % of time they stay open, though I've long forgotten what range you should be looking for.

-CTH

[Tomguy]

Disconnect your cold start valve (unplug it). Does it still flood when disconnected? It's possible the thermo-time switch has failed keeping it always energized, which could flood the engine. Especially if you have vacuum leaks, leaky injectors, or other conditions resulting in rich running.

Another possibility is fouled or failing trigger points always closed, keeping some of the injectors open nearly full time. With port injection there is still cross-flow, so other cylinders would be impacted by this and flood just like the ones right at those injectors.

[billhard]

Originally Posted by cth350

does the system maintain that 32psi when you turn the fuel pump off?
If it drops immediately back down towards zero, that pressure is leaking off somewhere.

How old is the line from the manifold to the MAP? If you don't know, then it's too old. It needs to be a strong enough line to not collapse and the ends should be clamped.

-CTH

Good ideas, I'll investigate.

Originally Posted by Tomguy

Disconnect your cold start valve (unplug it). Does it still flood when disconnected? It's possible the thermo-time switch has failed keeping it always energized, which could flood the engine. Especially if you have vacuum leaks, leaky injectors, or other conditions resulting in rich running.

Forgot to say in my first post but this was already tried, cold start isn't the issue.

Originally Posted by Tomguy

Another possibility is fouled or failing trigger points always closed, keeping some of the injectors open nearly full time. With port injection there is still cross-flow, so other cylinders would be impacted by this and flood just like the ones right at those injectors.

I am afraid of damaging these scarce parts, but it seems they warrant at least a visual inspection.

[Frank Reiner]

bh:

Re: Cold Start Inj. (CSI)
To ask the obvious: In addition to the electrical connection at the CSI, did you also disconnect (and cap) the fuel line? The valve itself could stick in the open position.

[Graham]

Common causes of overly rich mixture on djets are faulty temperature sensors or worn trigger points.

Specs for sensor resistors are in the FSM. (If you dont have it see tonka.ca m117). Using section 07
4, check other sensors too - esp the MPS.
Trigger point rubbing block wear cant be determined by inspection. Do a search here. There is a method of checking them by measuring the angle each pair stays open or closed. To adjust, look for Norbert or nordfisch. He has a low cost tool to assist in adjustment.

[Graham]

By the way, the FSM also explains how to do fuel pressure leak down test and how to determine cause.

[billhard]

Originally Posted by Graham

Common causes of overly rich mixture on djets are faulty temperature sensors or worn trigger points.

Specs for sensor resistors are in the FSM. (If you dont have it see tonka.ca m117). Using section 07
4, check other sensors too - esp the MPS.
Trigger point rubbing block wear cant be determined by inspection. Do a search here. There is a method of checking them by measuring the angle each pair stays open or closed. To adjust, look for Norbert or nordfisch. He has a low cost tool to assist in adjustment.

Thanks for the suggestions Graham, but can I ask what is tonka.ca? It seems to be a web site for buying tonka trucks.

[Graham]

My phone keeps adding the 'a' it should be tonk.ca