Crank no start, likey different
10-30-2015, 12:52 AM
#1
Crank no start, likey different
Yes there's a similarly titled active thread, but I have a bit more detail which I hope will enable somewhat more rapid diagnosis. I'm more of a bimmer guy, but this is the wife's and it's stuck in the garage. You know what that means... either I fix it yesterday or it may get towed to a shop. Last time we limped into the shop for trans work (only two months ago) I got hit with a $1150 tab. But the car ran and wife was happy....
Car is a '98 C280 Sport with 55,000 miles (only) so relatively young. Has been working well ('cept for the above mentioned trans issue). It won't start although it cranks strongly, so the battery is strong.
The car will occasionally catch then sputter and die within 5 seconds. Sounds like it may be a fuel pump? Or is it the crank position sensor?
There's a standard Bosch 4-pin relay just forward and left of the fuse box near the battery (not the seat relay, BTDT). I think this is the fuel pump relay, correct? The relay clicks when power and ground are provided to 85 and 86. Not tested but assumed good, is that power then flows from 30 to 87. If I put a jumper on the socket between 30 and 87 I expect the fuel pump to run - but it doesn't. Question: is that conclusive that the pump is shot or are we not there yet?
I am also suspicious of the crank position sensor and have seen where it lives. Not fun to access (I'm a big guy) but do-able. No apparent way to test without removal, and at that point might as well replace...? Cheaper by 75% compared to the fuel pump.
Need to look up the fuel pump access. Bimmers, you lift the back seat cushion and go in from the top. Benz....?how?
Car is a '98 C280 Sport with 55,000 miles (only) so relatively young. Has been working well ('cept for the above mentioned trans issue). It won't start although it cranks strongly, so the battery is strong.
The car will occasionally catch then sputter and die within 5 seconds. Sounds like it may be a fuel pump? Or is it the crank position sensor?
There's a standard Bosch 4-pin relay just forward and left of the fuse box near the battery (not the seat relay, BTDT). I think this is the fuel pump relay, correct? The relay clicks when power and ground are provided to 85 and 86. Not tested but assumed good, is that power then flows from 30 to 87. If I put a jumper on the socket between 30 and 87 I expect the fuel pump to run - but it doesn't. Question: is that conclusive that the pump is shot or are we not there yet?
I am also suspicious of the crank position sensor and have seen where it lives. Not fun to access (I'm a big guy) but do-able. No apparent way to test without removal, and at that point might as well replace...? Cheaper by 75% compared to the fuel pump.
Need to look up the fuel pump access. Bimmers, you lift the back seat cushion and go in from the top. Benz....?how?
10-31-2015, 03:24 AM
#2
Thanks for all the help, guys and girls. Not.
Turns out it's the fuel pump. The following path led to this diagnosis:
Engine refused to start though cranked strongly. Weak battery ruled out.
No codes stored, no fuses bad either under the hood or in the trunk.
Fuel pump relay bench tested good.
Jumper pins 30 and 87 on the pump relay socket, no action.
Jacked it up, propped it up, key in position 2 with pump relay jumper in place, banged on the silent pump with tool, pump stuttered weakly for a few moments only. Case closed, it's the pump.
Removing the pump will slosh gas all over you, be prepared to plug the big hose from the tank, it's about 5/8" diameter. I'll replace pump and filter tomorrow... like I have nothing else to do!
Turns out it's the fuel pump. The following path led to this diagnosis:
Engine refused to start though cranked strongly. Weak battery ruled out.
No codes stored, no fuses bad either under the hood or in the trunk.
Fuel pump relay bench tested good.
Jumper pins 30 and 87 on the pump relay socket, no action.
Jacked it up, propped it up, key in position 2 with pump relay jumper in place, banged on the silent pump with tool, pump stuttered weakly for a few moments only. Case closed, it's the pump.
Removing the pump will slosh gas all over you, be prepared to plug the big hose from the tank, it's about 5/8" diameter. I'll replace pump and filter tomorrow... like I have nothing else to do!
