95 Corolla DX 1.8L won't hold residual fuel pressure

[nbergevi]

I've got a '95 Corolla DX 1.8L hatchback that will stall as soon as you put it in gear and give it some gas, and will eventually stall in idle. It ran fine without any problems / stalling / hesitation up until 3 weeks ago.

Compression is 210 / 195 / 195 / 195, has about 19psi of vacuum, replaced plugs / cap / rotor button / fuel filter, wires hold good resistance (10k/foot), no Check Engine light, I feel vacuum when I place my hand on top of the oil cap hole. All of the cylinders look like they've been burning a little oil.


I took the air intake manifold apart and it was dripping with oil. I cleaned it out, cleaned the air intake / throttle plate / EGR valve / valve cover, put it all back together, and it didn't fix the stalling problem, (although I did make it almost to Wal-Mart and back before it stalled on me again).

I have a theory that it's a fuel starvation issue. I can't find a fuel gauge in town that has the banjo bolt adapter, but I know it won't hold fuel pressure after the fuel pump stops. I cracked the bolt at the top of the fuel filter enough to see a little fuel spray out when I crank it over. As soon as I hear the fuel pump stop I crack the bolt again and nothing comes out. Toyota manual states that it should hold 20psi for at least 5 minutes after the pump stops.

I have a theory that it's either the fuel pump or the fuel pressure regulator. There are no apparent fuel leaks under the vehicle, so I don't think it's the steel lines themselves.

I took the regulator off and used my air compressor to test it. When I change the pressure to about 35psi, and put the air hose up to the regulator no air escapes, but when I dial it up past 40psi air gets through the regulator.

I also put a clear hose on the return line from the regulator and put the other end into an empty gas can. I see fuel going down the line up until the point where the pump shuts off, so I can deduce that it's holding at least 35-40psi fuel pressure, (unless it intermittently fails).

I head somewhere that fuel pumps going bad can start out ok, but lose pressure as soon as they warm up, so it might explain why it will run for 5 minutes before it starts to stall.

I don't think it's the injectors, because as soon as the fuel pump stops there is no pressure - I would imagine it would take more time for an injector to bleed off that much pressure.

So - for all you Engine Guru's - Is it the Fuel Pump, could it still be the Fuel Pressure Regulator, or could it be something else?

And for extra credit - any ideas on the stalling issue? Could it be caused by the low fuel pressure?

[tashirosgt]

Just a few questions: When it stalls, is it easy to restart? You said the intake manifold was dripping with oil. Is the PCV valve also dripping with oil?

[nbergevi]

Sometimes it's easy to restart, sometimes it takes a while. Sometimes it will backfire white smoke (probably burnt oil) out the air intake.

I replaced the PCV valve, and took some engine degreaser to what I could reach on the baffles at the top of the valve cover. The port on the intake manifold that leads to the PCV valve looked like it had the biggest build-up of dried oil, so I believe that is where it was entering the intake.

After cleaning the intake and the valve cover baffles, I don't see any more oil coming into the air intake.

But - back to the fuel pressure question. I can get a used pressure regulator at the u-pull for $25 and a pump for $50. Which should I try first to see if it will restore residual fuel pressure? (I bought this about a year ago for $2k, and I don't want to sink too much into a vehicle that already has 195k miles).

[tashirosgt]

My one fuel pump experience was on a Chevy S-10. Having bought a new pump, we took out the old one to find there was a hole in the short length of tube on the intake of the pump. That was the only problem. So perhaps you should inspect the old pump before you commit to a new-used pump.

[nbergevi]

I have visually inspected the old pump. There didn't seem to be any problems with it, and the check valve held what little pressure I tried to blow into the tube with my mouth, (and honestly, how much pressure can you generate with your mouth while trying not to get gas on you lips...).

I'm tempted to hook it up and see how much water it can pump, but I don't know if that will ruin it or not.

[94_Rolla_Guy]

The regulator is easy to change, i think i would start there,

also it might be worth looking at the O2 for proper output and the coolant temp sensor for proper output either could cause a lean or rich condition that could be causing the problem,

Oh and the oil in the intake is no big deal mine does that too, if you wanna help that situation then add a catch can!

[nbergevi]

Do regulators fail intermittently, or is it all or nothing with them? Like I said, I hooked up my air compressor to test how much pressure the regulator would hold back, and it seemed to hold pressure up to spec both with vacuum applied and without vacuum.

Would it hold pressure, and then all of the sudden not hold enough?

My theory is that based on the number and complexity of parts, the pump would have the greatest likelyhood of failing compared to the regulator. Is this a sound theory, or does it not always work like that?

I pulled the old fuel pump, and it looked like the original Denso pump from '95.

[tashirosgt]

I admire your diagnosis procedures. For "engine often stalls", service manual for the '90 mentions these checks, in addition to the ones that you have done: vaccum leaks due to bad oil dipstick, EGR valve staying open. Clogged fuel filter. Clogged air filter. Check auxillary air valve.

Don't know if you problem depends on the weather. Will you engine run without the cold start injector? Could it be stalling as soon as that injector gets turned off?

I'm curious about what the mechanism is used for turning the pump on when the pressure drops. Does the vacuum line from the pressure regulator sense this. Is no-vaccum a signal for low pressure or is high-vaccum the signal? Anyone know?

[nbergevi]

This is a 1995, and I do not believe it has a cold start injector, (at least I couldn't find mention of it in the Chilton manual).

As far as the mechanism used to turn the pump on/off, it is always on when the car is running. The pressure regulator keeps the pressure in the fuel rail at a high pressure (35-40ish psi), and anything over that gets past the pressure regulator, down the fuel return line, and back into the tank.

The pressure regulator does have a vacuum line connected to it's diaphram. The more vacuum, the lower the fuel pressure. That's why when you step on the gas and open the throttle, it lowers vacuum in the intake manifold, and the regulator supplies more fuel pressure to the injectors because the engine is going faster.

I just read an interesting article online about diagnosing where the pressure leak is. I'm going to put the fuel pump back in, disconnect the ignition system, turn the fuel pump on, and pinch the return line from the end of the regulator closed right before the pump stops. If I still don't have residual pressure, (checked by cracking the bolt at the top of the fuel filter), I'll know it isn't the regulator. I'll do the same thing on the other end of the fuel rail where fuel comes from the filter, and if I still don't have pressure there, then I can deduce that it's the pump, but if I do then I'll know it's the injectors.

Bah - who needs a fuel pressure gauge?!?

[UFOtofu27]

Just put the new pump in while you have it apart, see what happens. If that doesn't do it, put the regulator in. You could be driving it by now. 195K is plenty of miles for a fuel pump. At least you shouldn't have to drop the tank to change it, just pull the back seat.

[nbergevi]

Well, it turned out it wasn't either. I finally borrowed a fuel pressure gauge that had the right adapter, and it turns out that it holds 37 psi fuel pressure.

After it died a few times running the fuel check, I jumpered the diagnostic E1 & TE1 to see if there were any codes, and for some reason both the O/D and Check Engine light were continuously blinking.

Does that mean the ECM is shot, or do I need to reset it and try again?