My 300SL won't start after long lay up

[CMB300SL]

Discussion Starter · #1 ·

New Member, Help needed please. My 1989 300SL won't start It has been off the road for 5 years. Things I have done so far:- 1) Found fuel pump relay, removed it and cover no obvious dry joints. 2) jumped terminals 30 & 87, 12.4 v at disconnected pump cables, only 9.4v when connected and no noise. 3) Removed bracket with pump filter and accumulator, replaced pump cleaned it all up and painted bracket then reconnected. Also drained all old fuel and replaced with new. 4) jumped 30 & 87 ,pump running 5) No Start. 6) Will fire with carb cleaner in the intake so assume ignition side OK. 7) Removed injectors cleaned exterior and then used a diesel cleaner on the inner, all gave a reasonable spray pattern. 8) Still no start. 9) Removed all pipe connections to fuel distributor fuel rises in all the distributor wells at same rate when depressing the plenum. 10) Haven't got pressure testing kit yet it is on its way however able to test flow from injectors at 5 & 6 They can be turned into a space,. Both injectors dispensed fuel with good spray pattern. 11) All back in place on turnover started and ran for v short time with big backfire then only the occasional kick but still no run. I think the initial run was due to residual fuel from previous testing still in the cylinders.
I am not sure where to go now, all advice gratefully received.


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[vijilants]

Squirt carb cleaner down the intake whilst cranking it.

If it fires up, your problem is fuel related. If it doesn't fire, it is ignition related.

 

[whitenemesis]

Squirt carb cleaner down the intake whilst cranking it.

If it fires up, your problem is fuel related. If it doesn't fire, it is ignition related.

6) Will fire with carb cleaner in the intake so assume ignition side OK.

 

[Flyinspanner]

You said no noise at pump.
have you verified that you actually have correct fuel pressure delivery?
Throttle body gummed up?
Air filter blocked?
MAF?
Crank Position Sensor?

do you have access to a code reader, that may indicate areas of concern. - maybe someone local to you can pop over and hook one up ?

 

[CMB300SL]

I have already squirted carb cleaner into intake and it fires, so am assuming that it is fuel related. Just got my universal fuel pressure tester and hooked it up. It shows 5.2 bar and 4.9 bar . The pressure should be around 6 and 6.4 bar so problem there. I am about to measure fuel pressure at the feed into the fuel distributor. If it is the same I shall be looking at the delivery system at the back. As I can't start the engine all these measurements were done with 30 and 87 bridged at the relay socket and the eha disconnected.
All further ideas would be most helpful.

 

[alabbasi]

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[CMB300SL]

Thanks, I only want to play with the distributor as a last resort and I do get a nice whistle from the injectors so I am hoping not to have to go there.
I have checked pressure from the pump and that is over 7 bar and I have know found out where the operational pressure is adjusted, but I can't find what the specs for the control and working pressures are for my 300 sl (103.98 engine I think). Does anyone know what they should be, i can't find them in my workshop manual.

 

[Paul Dilks]

Discussion Starter · #1 ·

New Member, Help needed please. My 1989 300SL won't start It has been off the road for 5 years. Things I have done so far:- 1) Found fuel pump relay, removed it and cover no obvious dry joints. 2) jumped terminals 30 & 87, 12.4 v at disconnected pump cables, only 9.4v when connected and no noise. 3) Removed bracket with pump filter and accumulator, replaced pump cleaned it all up and painted bracket then reconnected. Also drained all old fuel and replaced with new. 4) jumped 30 & 87 ,pump running 5) No Start. 6) Will fire with carb cleaner in the intake so assume ignition side OK. 7) Removed injectors cleaned exterior and then used a diesel cleaner on the inner, all gave a reasonable spray pattern. 8) Still no start. 9) Removed all pipe connections to fuel distributor fuel rises in all the distributor wells at same rate when depressing the plenum. 10) Haven't got pressure testing kit yet it is on its way however able to test flow from injectors at 5 & 6 They can be turned into a space,. Both injectors dispensed fuel with good spray pattern. 11) All back in place on turnover started and ran for v short time with big backfire then only the occasional kick but still no run. I think the initial run was due to residual fuel from previous testing still in the cylinders.
I am not sure where to go now, all advice gratefully received.


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With only 9.4 volts at the pump, have you verified the output from the battery?

 

[Paul Dilks]

Battery voltage should be greater than 9.4 volts? Is the battery sound?

 

[grober]

The CIS system is "powered " by two things fuel pump pressure and engine intake vacuum. Did you change the fuel filter?- or you may have a fuel tank outlet filter partial blockage --- check fuel pump is properly earthed----symptoms point towards a fuel delivery problem pressure or volume.

 

[CMB300SL]

The CIS system is "powered " by two things fuel pump pressure and engine intake vacuum. Did you change the fuel filter?- or you may have a fuel tank outlet filter partial blockage --- check fuel pump is properly earthed----symptoms point towards a fuel delivery problem pressure or volume.

The fuel pump is properly earthed, I get a full 12.6v . The 9.4v was on the old pump that was seized. I would appreciate it if you can tell me what the normal control and working fuel pressures are for the 300sl, or where I might find this data. I haven't checked the fuel flow yet, will do tomorrow. Cheers

 

[CMB300SL]

Still got the fuel flow to check and now the pressure at the injectors. I found the fuel pressure data for the distributor; lower chamber or control should be 4.9bar - 5.1 bar, upper chamber or working should be 5.2 bar - 5.5 bar and the difference is 0.4 bar. Mine therefore is pretty close. I do find my manual difficult as there is no index and so you have to trawl through the whole thing and it is easy to miss what you want. I shall also set up my remote starter switch so I can use the starter when I am looking at stuff under the bonnet.
I will report progress