delayed start problem

[Jim Poushinsky]

Hi folks,

I'm hoping someone can help me figure out what is causing my 1990 4 Runner (automatic, V6) to turn over for about 30 seconds before starting. The fuel pressure goes to nothing after it has been turned off and sat for about 10 minutes. When I turn the starter it takes about 30 seconds of cranking for the pressure to build up sufficiently to initiate firing and starting. The performance once started is fine, I've been towing 1/2 ton loads through the mountains no problem. The fuel pressure is normal when the motor is running. The vacuum pressure at the fuel regulator is low when cranking, but normal once it starts. I thought it might be a malfunctioning check valve in the fuel pump, but installing a new pump hasn't made any difference. I've replaced part of the fuel line with flexible pressure hose due to rust, and there are no visible leaks anywhere in the system. However there is a faint smell of gas when the Cruise Control is disengaged while slowing down. Occasionally the problem appears to correct itself for a day or so, and it will fire up within seconds. This may be related to being parked on an incline. Also, the Intake Manifold was off recently while doing a valve adjustment, maybe something was pinched or not put together tight? Any help in solving this mystery would be appreciated!

[Brian R.]

If I remember correctly, that model truck had a problem with the pulse damper getting abraded and leaking - by the firewall. See if you can replace this cheaply. The gas smell is part of this damper problem's diagnosis.

Might also be a faulty valve in the pressure regulator.

[Brian R.]

http://www.automotiveforums.com/vbul...d.php?t=282289

[Jim Poushinsky]

Thanks for suggesting the pulse damper Brian. I thought you were putting me on at first, as I had
never heard of such a part! However I managed to
find it in the manual, and just located it by feel out of sight at the back between the engine and the firewall. I'll have to remove the intake manifold to get at it. It's location is right under the noses of people seated in front, so a leak there that would indeed explain the faint smell of gas from time to time. I'll order the part on Monday and post the result when I change it on Wednesday.

[Jim Poushinsky]

Originally Posted by Brian R.

If I remember correctly, that model truck had a problem with the pulse damper getting abraded and leaking - by the firewall. See if you can replace this cheaply. The gas smell is part of this damper problem's diagnosis.

Might also be a faulty valve in the pressure regulator.

Okay, here's the update. I replaced the pulse damper. The plastic cover was cracked around the edges, and the neighbourhood showed white stains on metal which appeared to be caused by gas leakage.

While that may have stopped the gas smell when decellerating, it unfortunately did not improve the starting delay problem. It still takes between 15 and 30 seconds of cranking before the 3VZ-E will begin to
fire unevenly and then rev up. Once running it works just fine.

We have the original 1990 Toyota Shop manuals, and spent most of today running tests. I also crawled underneath with a bright light and verified all the gas lines are intact with no apparent leaks. The tests of various components could go on for days, so I'd appreciate any suggestions to help pin-point the source of the problem. First off, there are no engine codes, just the normal operation indicator. Also, there is a good spark happening long before the engine fires, indicating that the problem is fuel not reaching the cylinders.

We went over all the vacuum lines and tested the attached components. When cranking the vacuum needle (measured at Pressure Regulator and at the VSV type valves) goes from zero to about 10% of Normal, then rises quickly to Normal Range as the engine fires up. The manual does not tell us the normal operating pressure at cranking and start-up, so we don't know if this is okay, and the Toyota Help-Line and Toyota Dealers we called couldn't tell us. Does anybody know?

We tested the VSV for the FPU (fuel pressure up) and it passed all the book tests for vacuum and electrical operation, except one we made up. The VSV positive lead from the computer becomes live when the ignition is turned on, but we suspect the computer switches the ground wire on and off. Testing with the electronic Ohmmeter scored a 1 during cranking, which we assume means that the ground is floating rather than closed, so the VSV is not being actuated by the computer. Is this correct? If so, the computer is not signalling the proper start-up, which would point to testing the computer's input sensors for malfunction.

The delayed starting problem happens when the motor has been shut off for about 10 minutes, regardless if the engine is hot or cold. It is also evident to a lesser extent a minute or so after engine shut-down, and gets longer the longer it sits turned off, up to about a 30 second delay. On rare occasions it miraculously fixes itself (my wife thinks because its parked on a slope) and starts up fine for most of the day, only to develop the problem again next day. That happened maybe twice in the last month. Suggestions anyone? The pressure regulator doesn't appear to be receiving much vacuum at start-up, in fact it displays the same start-up problem with the vacuum totally blocked off in testing.

[Brian R.]

I suggest replacing the fuel pressure regulator. It is made to release fuel pressure when high manifold vacuum is obtained, like when deaccelerating, as well as controling the normal operating pressure. It sounds like the relief valve in the regulator is sticking open. You might be able to troubleshoot this by tapping on the regulator with a wrench when the engine won't start. If it starts because of the tapping, then you can be pretty sure the regulator is the problem. If it makes no difference, then it may or may not be the regulator.

The vacuum you measured while cranking and afterward sounds normal, but I don't have exact numbers for you.

[Jim Poushinsky]

Originally Posted by Brian R.

I suggest replacing the fuel pressure regulator. It is made to release fuel pressure when high manifold vacuum is obtained, like when deaccelerating, as well as controling the normal operating pressure. It sounds like the relief valve in the regulator is sticking open. You might be able to troubleshoot this by tapping on the regulator with a wrench when the engine won't start. If it starts because of the tapping, then you can be pretty sure the regulator is the problem. If it makes no difference, then it may or may not be the regulator.

Tried tapping the regulator while cranking and it made no difference. I don't have the special gasline fitting to test the fuel pressure at the regulator, so to test to see if there is a slow fuel/pressure leakage through a stuck partly open valve I disconnected and plugged the hose that connects the regulator to the fuel return line immediately after turning off the engine. I waited a half hour, reconnected the line 30 minutes later, and started the engine with no more than a 5 second delay. Likewise for a second trial. Likewise for a third trial with a 75 minute interval. Looks like we have located the problem, the stuck valve in the regulator is slowly leaking pressurized gas back into the gas tank, so there is no pressure until the gas pump builds it up while cranking. The fact it is gradually cranking longer and longer before starting indicates the valve is sticking further open, which would account for the roughness when it finally fires. I'll be installing a new fuel pressure regulator in the morning, and let you know what happens.

[Brian R.]

Good luck

[Jim Poushinsky]

Originally Posted by Brian R.

Good luck

Not today. The new pressure regulator didn't correct the delayed start problem, but it appears to have cured the roughness on start-up. We also found some vacuum lines with small leaks that we fixed. Once it starts the engine runs beautifully. We also disconnected the battery to reset the engine codes, but still get no codes warning of a problem. I'm about to leave on a 3000 km trip towing a 1000 lb. trailer through the mountains. Looks like I'll just have to put up with the delayed start until I get back (successfully completed the same trip earlier this year).

At least I now know the fuel filter, fuel pump, pulse damper, and gas regulator are all new and working properly. I finally located a gasline fitting to test the fuel pressure at the regulator, but don't have time to do this just now. Assuming the pressure is still dropping in the line immediately after shutting off the engine, what else could be causing this??? We checked the fuel lines again and still no indication of a leak, not even any fuel smell. And there is a strong vacuum in all the vaccuum lines when the engine is accelerated from idle. The fact that everything works fine when running and there are no code problems indicates the computer is most likely okay.

The vehicle does have close to 300,000 km on it, and about 120,000 km ago my son rolled it onto its side in a ditch, and the engine stalled when the engine oil was sucked through the manifold and filled the cylinders. There are still visible traces of oil deposits in the manifold, despite all the cleaning out I did back then. Maybe this has finally caused something to fail, but what? Could there be a problem with the fuel injectors that causes the pressure to drop in the gas line after shut-down, but doesn't interfere with driving?

ould it be a malfunctioning sensor giving the computer incorrect info for start-up? If so, why does the problem happen regardless whether the engine is hot or cold? It remains a mystery!

[Brian R.]

The drop in pressure could be the pump valve (replaced), the pressure regulator (replaced) or a leaking injector.

Yes, it could be a sensor. Testing the fuel pressure will give you a clue. If the fuel pressure is being drained, then it's not a sensor. If it doen't come up quickly, then it may be a sensor.

[Jim Poushinsky]

Originally Posted by Brian R.

The drop in pressure could be the pump valve (replaced), the pressure regulator (replaced) or a leaking injector.

Yes, it could be a sensor. Testing the fuel pressure will give you a clue. If the fuel pressure is being drained, then it's not a sensor. If it doen't come up quickly, then it may be a sensor.

Hi Brian et al,

I'm back from the North. The 4-Runner performed exceptionally well, except for the worsening start-up problem. I towed a loaded trailer both ways through the mountains, and discovered the new parts in the fuel system (fuel filter, gas pump, pulse damper, and pressure regulator)greatly improved the mileage/performance - I'm now going 450 km per tank of gas instead of 350 km! The loss of gas pressure after turning the engine off has worsened, so I replaced the cold start fuel injector. That didn't help, which leads me to suspect the main fuel injectors as the source of the leak. The fact that the engine runs well when it does start, and the fact there are no engine codes which would signify a sensor problem, supports this hypothesis. Also, the battery ran down in the cold weather to the point where it wouldn't turn the engine without a boost. It immediately fired with the boost, so trying to start it, even without the starting motor cranking, activated the fuel pump and built up pressure. When I finally got home after a month on the road the car died the big one, and now cranks but won't start, so I assume it is no longer able to build sufficient gas pressure.

Unfortunately I can't afford the $1000 to replace all the injectors, so my question is, how do I clean them? If I remove them is there a solution I can place the tips in to dissolve any crap? I will replace the o- rings, as they may be the source of the leak. The cold start injector was covered with black baked-on dried oil residue that must have been left over from the time 8 years ago when my son rolled the vehicle and the motor seized hydraulically as the oil filled the intake manifold.

Any tips on cleaning the injectors and fixing any other potential leaks
in the fuel rail would be appreciated!

Cheers,
Jim Poushinsky

[Brian R.]

http://www.rceng.com/

will clean and detail the injectors. This is the only place I have a reference for. You can try putting some Chevron Techron or equivalent into your gas tank and see if that clears up the problem of cleaning them. O-rings are cheap..

[4Wheel]

Hello,
Have the injectors cleaned, they will flow test and install new screens and "o"rings. $20ea.
Did I miss a pump replacement?
The engine codes can by purged just by pulling the ECU fuse in the engine compartment.
The 4Runners have some codes that only register on the second subsequent trip.
Are you enabling the codes with the jumper wire?
Have you tested the fuel pressure witout the engine running using the FSM procedure??

http://personal.utulsa.edu/~nathan-b...ne/99fuelp.pdf

Have you done any diagnostics on the EGR sysstem? The EGR valve?
http://personal.utulsa.edu/~nathan-b...77exhaustg.pdf

Good luck

[Jim Poushinsky]

Well, I didn't take out the fuel injectors. We repeated a pressure test on the gas line before it goes into the fuel rail. The pressure was barely sufficient to start the vehicle, had to press on the accelerater to get it to start. As soon as the switch turned off the pressure dropped to zero within a few seconds. When the line was taken apart to remove the tester there was no pressure in the line, and surprise - no gas! Since the line was not leaking gas to the outside, the only logical explanation is that it was leaking in the gas tank. Since the gas pump was new and the check valve worked, this meant the sending unit had to be leaking inside the gas tank. We removed the tank and sure enough, there was a break in the gas line tube where it passes through the sending unit plate. The folks who reconditioned the tank had soddered it there, but it obviously hadn't held. The replacement sending unit from a scrapyard also proved to have a leak there, only this time it was apparent because it was outside the tank, but again rusted through at the tube. Looks like I'll have to buy a new sending unit from the dealer, since the old ones in Canada are all rusted out from the salt used on our roads in winter. Too bad there wasn't a way to get one from a scrapyard in the sunny south where y'all don't have our salt spray problem. It's a a 1990 Toyota 4-runner, 6 cylinder, automatic, just in case someone has a sending unit.

Cheers,
Jim Poushinsky

[4Wheel]

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