Hello Guys! This is my first visit to V6 board. Anyway, my aunt has a 91 RS w/ the 3.1 liter V6. She brought the car to me because it is stumbling, almost like it's running out of gas at 3/4 - WOT. I'm not familiar with the V6's and if it were carbed I'd have an idea of how to diagnose it. My only experience with EFI is my 89 RS, and that is limited. My question is: Have any of you guys had similiar problems, and if so what was it??? The only thing I can really think of clogged injectors or possibly low fuel pressure, but I wouldn't really know how to check it on her car (quickly, anyway) I'm looking for an easy way out, because I really don't have too much to fool with it, but I'd like to help her out and save her some $$$ Thanks in advance guys.

P.S. She says its does it much worse when the car is not fully warmed up, if that helps!!

 

2 things I can think of would be a clogged fuel filter or the Ignition System is breaking down at high RPM.

You can check the filter by taking it off and blowing through it. There shouldn't be much resistance, if any.

To check the Ignition, an oscilloscope would help you a lot. If you know anyone at a shop with a scope, hit them up. Most people don't have access to them though.

EDIT: I just read the part about it not being warm when it does it. That would almost completely eliminate an ignition problem. I'd focus on the fuel system first...starting with the filter.

 

I'd check ignition (cap & stuff) just to easily eliminate it.
Also open hood at night, engine running, NO LIGHT to check/see jumping of sparks.

 

If your looking for the schrader valve to check fuel pressue its inbetween the distributer and the plenum (kinda right underneath the back of the plenum). I would say def check the fuel filter too(heck, just change it). And def look for jumping sparks at night. I was having the same problem, turned out my spark plug boot next to the egr valve (middle passenger side) dried out and cracked from the excess heat from the egr and the spark was jumping; never getting to the cylinder.

Inspect wires, fuel pressure, cap, etc....you know, the easy stuff first....then I would would say maybe take a look at the 02 sensor...if it hasn't been changed and is dirty or old it could be misreading the exhaust and not sending the appropriate fuel to the cylinders....get what I mean. FYI, after I trouble shot my hesitation and changed out alot of stuff (fuel filter, cap, rotor, ignition module, 02 sensor) my gas milage jumped 100 miles a tank....and all it was was worn out boot....hahah...

 

I'd agree about the tuneup area... look for my message called "major tuneup repost". Also check the timing.

After you check out all that stuff (or replace it, it's probably the original stuff, eh?), you could also check the following:

TPS voltage @ idle (for v6, should be 0.55 volts +/- 0.05 volts)
exhaust system leaks (especially at manifold and y-pipe)
bad alternator or dying battery
vacuum leak (throwing off fuel regulator)
clogged IAC passageway/dirty IAC motor pintle/dirty throttle body

If the car is cold, it's in open loop operation, and the fuel system is definately a suspect. If it's running rich or lean, the comptuer doesn't know, since it's in open loop (and not reading the oxy sensor). It could also be a problem with the CTS (coolant temp sensor); that helps "guess" at the correct a/f ratio during open loop.