long crank `87 560SEL

[vintageOEM]

Hi guys,
Quick question: my `87 560SL takes a pretty long time to crank before it starts, usually about 3 attempts, 5-8 sec each. I know that both fuel pumps filters and accumulator are new, what could cause this? Cold start valve? FPR? Check valves?

[Sugar Bear]

Yes to the items mentioned and the check valve at the fuel distributor or fouled spark plugs from worn guides and seals. I'd start the diagnostics with a compression test, a read on the plugs and a fuel pressure test to see if the system is holding pressure.

How does it run once it warms?

[vintageOEM]

Once it warms up its fine, but the initial start is always hard

[t walgamuth]

could be cold start injector.

[porkface]

weak spark will do that also. a cold start puts the most stress on the ignition system. look for white flashover on the bracket on the coil. seeing that means spark is taking the path of least resistance. old or fouled plugs, cap, rotor wires, etc.

i forgot. a weak crank sensor can do that also. need to scope it and watch the wave form. should see 1 to 3 volts ac as it reads the teeth on the ring gear. lower than 3 ac will not generate enough signal for the ecu to use. hope that's not it, m116/117 crank sensors have been nla for years now.