safemode

iTrader: (1)

Ok, i've posted before about how my car will suddenly die (yet all accessories stay on like it's not dead) if i'm in gear and idle after driving or shifting from park to drive or reverse. It idles according to the guage at around 800 or so in park and definitely around 750 in gear. Now comes the new info. I got a digital advance timing light for 100 bucks (accurate up to 9,999 rpms, really nice) and it measures the rpms at about 200-250rpms lower than whatever the guage is saying. I'm inclined to believe the timing light, and this would mean that my car actually idles at around 500rpms in gear and about 600-650 in park. If low idle rpm is why the car dies, then I've got to find out why the computer thinks i'm idling higher than i actually am. If it's just the guage then it may need replacement.


I think this discrepency only occurs in low <1500 rpm range because I cruise at 2000rpm doing ~70mph and that's pretty much about what i should be doing i think. So would there be a way to check if the computer is picking up the signals from the crankshaft position sensor (I assume there is one for low rpm use) or if it could be something else, could someone point me in that direction.... it's either this or I guess i'll have to wait until i can get my datalogging / chip writing setup going this summer.

The car is a (as far as i can tell, I'm the 3rd owner) pretty much stock 92 rs 305 tbi.

Danno

It's not unusual for the tach to be off. Thats why most manuals say to use an external tach when troubleshooting or testing. 200 rpm is a lot though. Dying can be anything. Check fuel pressure, a clogged fuel filter is not uncommon. Have you serviced the throttle body. They should be cleaned once a year. I had trouble with my 89 stalling when cold. I cleaned the TB and replaced the IAC valve and the problem cleared. Could also be ignition but try the easy stuff first. Many times a can of fuel system cleaner can solve minor problems. LOL

therckid

ummm did you disconnect computer controlled timing advance?

if not wont that mess up any reading you get?

Tibo

iTrader: (15)

200 RPM is actually quite common. All of the cars I have played with, including my own have said around 200 RPM.

Benm109

It's actually quite common for the stock tachometer in the car to be off. Mine and countless other 3rd gen owners have tachs that read anywhere from 200 to 1000 RPMs off (usually read too high) of what the engine is actually at, if you don't believe it than just do a search. The problem with them is usually a capacitor or the printed circuit board goes bad over time and makes the tach read off.

You can't trust the stock tachometer in our cars, because they are really just a trim piece, not an accurate tuning device.

Just because the tach is reading high, does not mean that the computer is reading high also. Hooking up a scan tool or datalogging will let you know for sure if the computer is reading the right RPMs or not. I'd be willing to bet that it's just the tach that's off.

One more thing, there is no crankshaft position sensor on your car, or any stock 3rd gen motor for that matter.

How long has it been since the car's had a good tune-up (spark plugs, spark plug wires, cap, rotor, oxygen sensor, fuel filter, etc.)? Have you checked timing and/or fuel pressure recently?

Tibo

iTrader: (15)

On a side note, My ecm does read 200 RPM lower than the tach. I always have to take that into consideration when datalogging.

safemode

iTrader: (1)

fuel filter is brand new, not clogged. The injectors need to be cleaned a bit since it doesn't fog when idling, it sprays. I dont really think that could be causing the stalling, without datalogging though, it's impossible to know what is going on. I definitely disconnected the ESC (electronic spark control)

The reason i ask about the tach and the ecm is because according to my tach, i'm idling exactly what i should be according to spec, I should be idling at 850 or so in park and 750 in gear and that's what the tach says for the most part. In reality though, i appear to be doing about 200 less than that. That's why i think it's more than just the tach being miscalabrated. This happens in the summer just as much as in the winter and i've cleaned the throttle body and IAC and it supposedly had a full tuneup last summer.


It used to be set for quite a large retard in timing, I just recently set it for 8 degrees advance and it's running great. I haven't really let it idle down to stall though, I guess i should stop driving two footed for a while to see if the timing change does anything. I guess the previous owner was doing some voodoo to get around emissions and set it to a huge retard in timing (possibly to run a higher alcohol mix?) .

In any case, it looks like i'm screwed until i get some datalogging done. Would be great if there was a eastern Pa thirdgen club (hint hint) heh.

safemode

iTrader: (1)

Oh, and one more thing i found interesting when changing the timing. I disconnected the ESC before turning the car on, did the timing, turned it off and plugged it back in. According to the service repair manual I should have recieved a check engine light due to the thrown code caused by the computer having the ESC disconnected, but this never happened. I still get my EGR code thrown when cruising but the light never came on when i restarted the car after doing the timing. Just another thing to have to look at when i eventually get this thing under a datalogger.

Danno

Exhaust gas into the mixture at idle WILL cause it to stall. I would service the EGR system, they can get carboned up and cause all sorts of driveability problems.