Overnight misfire

[strang3majik]

Ok, I'll have to pull the line off the fpr.

When I pull the vac line off of it while its running, idle fuel pressure jumps to about 37-38 and drops to about 35 when I give it throttle.


So, my guess is the fuel pumps are good as is the fpr :/ Also, went out and did it again, I lied, it does not drop when you goose the throttle, only when you let off does it drop to 25 for a split second, or on decel.


If you were me, what would you check next? haha.

[jlevie]

Everything you are describing suggests to me that the FPR and fuel pump are equally suspect at this point. If I had to guess on just one, based on the symptoms I'd pick the fuel pump.

[strang3majik]

Everything you are describing suggests to me that the FPR and fuel pump are equally suspect at this point. If I had to guess on just one, based on the symptoms I'd pick the fuel pump.

Whats making you think the fuel pump is bad? I thought the pressures were in spec?



Its running rich, I just figured if the pump was getting low pressure, the injectors wouldn't be able to spray, and would more so dribble fuel in and cause it run rich since the flow can't really be controlled.

It seems that the pressure isn't really, low, so I'm not sure if that theory applies or not. :/

[strang3majik]

Ok...something else I tried, I unplugged the throttle position sensor, idle jumped to about 1500rpms after it sat there for a minute, tried driving it up my driveway, it ran smoother. Nothing in terms of power, but it was smoother.


And I just read that they only detect idle and WOT. So that makes no sense.

[strang3majik]

Ok, I think I'm on to something. How do I test the coolant temp sensor? All this time I've been unplugging, checking the wrong one.

When I unhooked the white two prong plug, and hooked it to the brown sensor in the thermostat housing (I know, wrong resistance, etc), the car ran much better and a lot closer to what it used to. Idled high, but ran much smoother.

So, what should that sensor read while hot?

[jlevie]

Whats making you think the fuel pump is bad? I thought the pressures were in spec?

While the loss of residual pressure could be the FPR, one usually sees funky rail pressures from a bad FPR. So the odds favor a bad fuel pump.

Its running rich, I just figured if the pump was getting low pressure, the injectors wouldn't be able to spray, and would more so dribble fuel in and cause it run rich since the flow can't really be controlled.

It seems that the pressure isn't really, low, so I'm not sure if that theory applies or not. :/

I presume you are saying that it is running rich because the exhaust has a fuel smell when the engine is idling. You almost certainly have intake leaks which result in a rough idle caused misfires and partial misfires. That will make it seem like the engine is running rich.

Ok...something else I tried, I unplugged the throttle position sensor, idle jumped to about 1500rpms after it sat there for a minute, tried driving it up my driveway, it ran smoother. Nothing in terms of power, but it was smoother.

And I just read that they only detect idle and WOT. So that makes no sense.

When you disconnect the TPS (or ICV) the vane opens fully admitting more air and thus raising engine speed. In most cases intake leaks don't get worse with an increase in engine and thus they have less affect at higher engine speeds. So it is no surprise that the engine ran better.

Have a smoke test run and fix the leaks, replace the high pressure fuel pump (and filter), replace the O2 sensor, and adjust the valves. If the idle is still a little rough, replace the plugs, ignition wires, distributor rotor, and cap.

[strang3majik]

Well, the idle was the smoothest part about it, its driving that it was chugging. Also, plugs were put in not even a tank of gas ago.

As far as the richness, I've gone through half a tank in less than 50 miles of driving.

And I just checked the coolant temp sensor, at operating temp, its reading 259ohms.

That sound right?

[jlevie]

Using the stock 80C thermostat the ECT would have a resistance of 330 ohms. And wih a 75C thermostat 382 ohms. Yours reads low, which could mean the engine is hotter than normal or the sensor is not quite right. But if the engine is hotter or the DME thinks it is fuel use will be reduced.

A half tank in 50mi corresponds to about 7mpg, which is probably more than what an ETA can consume at WOT at the redline. Are you sure you aren't leaking fuel?

[strang3majik]

Using the stock 80C thermostat the ECT would have a resistance of 330 ohms. And wih a 75C thermostat 382 ohms. Yours reads low, which could mean the engine is hotter than normal or the sensor is not quite right. But if the engine is hotter or the DME thinks it is fuel use will be reduced.

A half tank in 50mi corresponds to about 7mpg, which is probably more than what an ETA can consume at WOT at the redline. Are you sure you aren't leaking fuel?

Ok, so, in other words, that would actually be helping me? And temp gauge is right below half.


And that is right around what the mpg gauge on the dash reads anytime I'm actually giving it gas. Also, lets sy between 50-75 miles. If I'm hardly on the throttle either down hill or on completely flat surface at cruise it's between 15-20.

Before it'd be nothing to be 25+ at cruise. And no leaks.
(though after sitting for an hour, fuel pressure went to zero, took the vac hose off the fuel pressure regulator (while the engine/key was off) and the pressure shot up to 30. Is that normal?)


The last things I have on my list that could've occurred quite like they have:
Crank sensor (not sure how important it is on this engine)
Timing jumped


or...this has occurred to me, but, bad gas.

[jlevie]

The purpose of the vacuum line to the FPR is to reduce rail pressure when the throttle is closed. That allows the DME to better control the minuscule amount of fuel needed then.

Try what I've suggested. If the problem persists the other possibilities can be investigated.

[strang3majik]

Well.....................

I feel like a retard but have had a great amount of relief.

Called a friend of my father's who used to work on these back in the day, and he told me to pull the distributor cap and make sure all that looks good since the injectors get when to fire from in there.

Well...I pulled the cap, and damn if it was't cracked and had a burned spot where it grounded out. Put a new cap and rotor on it and this little car rips now, better than it ever has.


I would've never guessed they had any correlation, but, I guess that would explain the random misfire that was never any cylinder, and why there was unspent fuel.


I'm sure somebody mentioned it, and if you did, I apologize for ignoring you. But thanks guys for all your help!

I'm still going to look into all the vacuum leaks and probably replace the coolant temp sensor since I'm sure it can still run better, along with change the oil since it was running so rich :/ But, it actually has some get to it now, I'm actually impressed with the little eta motor...hahah.


Thanks again guys! Now I'll go make my official intro post.