240 starting problem in hot weather

My 1990 240 with 155,000 miles on it has suddenly developed a
reluctance to start when the weather is hot- 80s and above. It seems
to not be getting sufficient fuel during startup, as giving it a little
gas gets it to start. Idle is a little lopey for a few seconds and
then evens out, sometimes revs highly for a few seconds. At 65-75
degrees, it starts normally. I checked for fault codes: 1-1-1 so
nothing there. All the vacuum hoses seem to be OK.

Recent work done on the car was replacement of AMM and airbox
thermostat 3000 miles ago, replacement of master cyclinder, and 4 new
tires. The car ran superbly after this, until about 2 weeks ago.
Other than the starting problem, the car runs great.

Any suggestions as to where to start looking? Thanks!

 

Classic signs of a dead intank pump. You can hear the pump with the
filler cap removed and engine running if you put your ear right beside
the filler neck. There's a separate fuse for the tank pump in the main
fusebox.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Thanks for that suggestion. I can hear the pump running at the filler
neck and in the trunk when it's open, for that matter.

 

The bellows between the in-tank pump and the fuel line could be torn also -
the effect is pretty much the same. It is not available separately ($300 for
a fuel sender assembly???) so most of us replace it with regular fuel hose.
Unfortunately, it isn't easy to check. Inspection is 95% of replacement.

Mike

 

So the in-tank feeder pump could be running but fuel still isn't
flowing to the main pump?

 

Exactly - when the bellows (which allows the in-tank pump to conform to the
actual depth of the tank) tears, gasoline pours out the hole back into the
tank instead of being pumped to the main pump. Replacing the bellows with
fuel hose tends to make the pick-up hover above the bottom of the tank a
bit, but I don't let the tank get down to the last gallon anyway.

Mike

 

<snip>
An easy test is to pull the hose off the back of the main pump and
insert and old carburetor style fuel pressure gauge. If you bump the
starter a few times you will see the fuel pressure devloped by the
prepump. It should only be a couple psi. You can also measure the amp
draw across the prepump fuse (#5 I think) and it should draw between 1
and 5 amps or so. If you run power to the fuse with a jumper wire to run
the prepump independently, listen at the filler neck with tank less than
half full, if there's a leak in the bellows pipe then you will hear fuel
splashing back into the tank.

Bob

 

Thanks for the suggestions- turns out to have been the fuel pressure
regulator.