yet another thread :/

would a bad in-tank pump cause a weak and uneven idle for 10-15 seconds after first starting? it only does this sometimes, but interestingly it got much worse (and even died after starting once yesterday) when the weather was much hotter than it has been in a while. Would ambient temperature influence a fuel supply problem? after a few seconds of anemic idle, the car runs absolutely fine, and it has no problem starting right up again after it has been running.

Yesterday, when the problem got noticeably worse, I had a full tank of gas. I haven't seen a relationship between this symptom and amount of gas in the tank.

I'm nearly certain now that the in-tank pump is dead. I've tried the listening method at the filler opening but it is difficult to tell if the pump is running because I can hear the loud main pump so clearly through the tank--and the main pump is definitely making that unhealthy sound (I went through all of this on my 940).

I put in an order for a new in-tank pump, but I'm curious to know if a malfunction there in the fuel supply chain would cause this particular symptom (and why a hot day would make it worse).

1/ What year is this 240?
2/ Is there a hard/slow start condition accompanying the erratic idle?

Not so sure about the 240, but on other Bosch FI systems I have experience with, the car starts in an "open loop" condition and runs for a few seconds before going "closed loop". During "Open loop" the OXS input (perhaps others, too) is not checked by the computer, so the FI operates in an enriched condition determined by ambient temperature. If all else fails, perhaps this is something to consider.

As you well know, there are multiple problems which could cause this symptom. It may be tedious, but approaching the problem methodically and not swapping out parts unless they are demonstrably defective will lead you to the solution.

Rich (near Pittsburgh)

Yes, ambient temp has a marked effect on fuel distribution, if one or more of the elements of the system is compromised.

http://cleanflametrap.com/transferPump.htm
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Art Benstein near Baltimore


Those who jump off a Paris bridge are in Seine.

what year 240? wagon or sedan? recently run your tank dry?

You can disconnect the main pump so you can listen for the in-tank pump. The connector (single yellow wire) is below the rear seat on the drivers side. Easier on a wagon since the seat is designed to be flipped up.

Consider trying the jumper method at the fuse block to test the in-tank pump. It will depend on the year of your 240, but with a jumper wire you can test both pumps independently with the car off. Search the RWD forum for 'fuse jumper fuel pump' for instructions.

I had similar symptoms that rapidly devolved into a car that wouldn't start. The main pump had failed (12 years ago). So far I have never had to replace in-tank pumps in owning 5 different 240s. I did have one that got clogged up from bad gas (sat too long) but I was able to clean it up and get it operating again using rubbing alcohol. Only other in-tank issue was the small rubber hose on the end of the in-tank pump cracked apart but wouldn't cause problems until the tank was half empty.

Consider also checking for voltage at each pump during run conditions and also check vacuum hoses for the Fuel Pressure Regulator.

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'80 242, '82 245 'worktruk', '83 244 Turbo, 83' 242 'volcamino' + a massive dodge van

Not that familiar with the 200. But on the 700 you can isolate each pump with key on and see if both work. Involves pulling/jumpering fuses. Or you can jumper the fuel pump relay with each fuse pulled to isolate also.
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