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740 Turbo fuel problems? 700 1988

posted by  Rtilghman on  Mon Jul 5 08:53 CST 2004
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I'm currently dealing with something similar. Car runs strong when it runs, will suddenly have wierd tach responses and idle fluctuations, may stall or die, oftern just won't start, then will start strong for no apparent reason, etc. Your problem sounds similar, though it COULD be completely different in source (its just tough to tell with these kinds of issues).

First check the Fuel Pump Relay (large white relay, middle row, far left). Old relays can develop weak solder points that affect the relays functionality. If its new or known good or checks out move on.

Next make sure the fuel pump actually works. Jump socket 30 and 87/2 directly with a piece of wire capped with two male terminals. The main fuel pump should IMMEDIATELY come on when you do this (you'll hear it beneath you). If you want to test the pre-pump turn the key to position II while doing this and listen at the filler hole... if its working you'll hear an OBVIOUS whir in the tank, if not its dead or not running. FYI You don't need the pre-pumpo to run the car, so this is all gravy. If the main pump works move on.

Next you should make sure that fuel is actually reaching the rail when you have everything starting normally. Simple test is to just unplug the fuel line at the rail, put it in a bucket, and try to start the car normally. CAVEAT: BE CAREFUL. Obviously gas is flammable and you don't want to get gas all over the engine when your cranking it, but it is the easiest way to quickly figure out if you have no gas. If gas pumps out fuel is cycling, if not you have a fuel issue. If the former I would probably lean towards injector electronics (supporession relay, etc.), if you the latter I might look at the Hall Effect Sensor in the distributor.

Then just keep isolating things down until you figure it out. In my case I'm jmore or less convinced I have a faulty Hall Sensor. Its a sensor in the distributor that can trigger a no fuel condition, and since my pumps work but it won't run fuel when starting and my relay is new and wiring checks out I have to assume thats it.

Hopefully someone with more knowledge than me will post to correct me or help you more.

Best,
rt






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