Fuel Rail Pressure Drop After Vehicle is Turned Off

[DTCsk8er]

I've been randomly encountering a stumbling start on my 2000 LC with 306k on the clock. This usually happens after vehicle has sat for 1-3 hours, and still somewhat warm. Sometimes the stumble will cause the engine to die, and the subsequent start cranks eventually lead to engine stumbling back to a start. Cold start is very consistent, and the engine roars to life every single time. About 80% of the time, I don't ever encounter this issue. When running, I get no hesitation, and engine is humming away as usual; usually hit about 11MPG mixed driving loaded up and with larger tires.

In effort to try and diagnose the problem, I installed an adapter on the fuel rail that allowed me to hook up a fuel pressure gauge to monitor things. Below is what I used incase anyone ever needs to do the same:

1/8 NPT Valve
Russell 640700 Banjo Bolt
BOSCH Fuel Pressure Tester

So far, here are my observations:

1. While running, the vehicle is right at 41-42PSI. No pressure change when revving engine, and seems consistent.
2. There is no abrupt drop in pressure when shutting off, it is a slow progression it seems.
- 0min after shutoff = 42psi
- 5min after shutoff = 38psi
- 15min after shutoff = 34 psi
3. The FPR is getting absolutely no vacuum from the intake box even with the throttle open and RPMs in 2-3k range. Odd, but as I don't see any PSI changes with increase of engine revs, this may be normal?

I did replace my #7 failed coil this weekend, but I don't think that could be related.

Has anyone had experience observing their fuel pressure before and after running? I expected some drop, but from what I can find searching this seems to be a bit excessive. I may find a pinch point on the fuel line and clamp, to determine which side of the clamp is losing pressure. Could be FPR or leaking injector(s), or perhaps the check valve on the gas tank.

I am also carrying the gauge with me, so that I can take note of the pressure when the engine stumbles and dies.

 

[Dusten]

I've been randomly encountering a stumbling start on my 2000 LC with 306k on the clock. This usually happens after vehicle has sat for 1-3 hours, and still somewhat warm. Sometimes the stumble will cause the engine to die, and the subsequent start cranks eventually lead to engine stumbling back to a start. Cold start is very consistent, and the engine roars to life every single time. About 80% of the time, I don't ever encounter this issue. When running, I get no hesitation, and engine is humming away as usual; usually hit about 11MPG mixed driving loaded up and with larger tires.

In effort to try and diagnose the problem, I installed an adapter on the fuel rail that allowed me to hook up a fuel pressure gauge to monitor things. Below is what I used incase anyone ever needs to do the same:

1/8 NPT Valve
Russell 640700 Banjo Bolt
BOSCH Fuel Pressure Tester

View attachment 2917522
So far, here are my observations:

1. While running, the vehicle is right at 41-42PSI. No pressure change when revving engine, and seems consistent.
2. There is no abrupt drop in pressure when shutting off, it is a slow progression it seems.
- 0min after shutoff = 42psi
- 5min after shutoff = 38psi
- 15min after shutoff = 34 psi
3. The FPR is getting absolutely no vacuum from the intake box even with the throttle open and RPMs in 2-3k range. Odd, but as I don't see any PSI changes with increase of engine revs, this may be normal?

I did replace my #7 failed coil this weekend, but I don't think that could be related.

Has anyone had experience observing their fuel pressure before and after running? I expected some drop, but from what I can find searching this seems to be a bit excessive. I may find a pinch point on the fuel line and clamp, to determine which side of the clamp is losing pressure. Could be FPR or leaking injector(s), or perhaps the check valve on the gas tank.

I am also carrying the gauge with me, so that I can take note of the pressure when the engine stumbles and dies.

The fuel pressure is usually maintained by a check valve in the pumps.

But the truck should build pressure when you key on so rails losing pressure while sitting shouldn't be an issue.

 

[87warrior]

34 psi 15 minutes after shutdown is well within spec. FSM indicates fuel pressure should be above 21psi 5 minutes after shutdown (sorry, the picture cut off the 5 minute notation).

In 2020 I spent a lot of time chasing what I thought was a fueling issue. The fuel pressure never really changed whether the FPR vacuum sensing hose was connected or not, even with a new FPR.

In regards to the stumbling when starting on a 'warm' engine, have you checked to see what your coolant temperature and mass air flow sensors are reporting when it sumbles?

 

[94SRUNNER]

Curious if you have looked at the condition of your coil packs?

 

[DTCsk8er]

34 psi 15 minutes after shutdown is well within spec. FSM indicates fuel pressure should be above 21psi 5 minutes after shutdown (sorry, the picture cut off the 5 minute notation).

View attachment 2918310

In 2020 I spent a lot of time chasing what I thought was a fueling issue. The fuel pressure never really changed whether the FPR vacuum sensing hose was connected or not, even with a new FPR.

In regards to the stumbling when starting on a 'warm' engine, have you checked to see what your coolant temperature and mass air flow sensors are reporting when it sumbles?

Awesome! Thanks for posting that image! I must have missed that in my FSM reading. I have not really paid much attention to temp and MAF when it's stumbling (hasn't done it yet in the last 3 days). I keep an eye on the vitals next time it does it for sure!

 

[DTCsk8er]

Curious if you have looked at the condition of your coil packs?

Well, I replaced #7 this last weekend because it abruptly failed (threw the usual misfire code). I didn't pull the remaining 7 coils, but they all appear to be the same age (probably original w/ 300+k on them) and likely are a ticking time bomb. Looks like the PO from his records changed plugs out (80k miles ago now), but didn't replace any of the coils

Here is a few photos of the new DENSO vs old:

The old coil tube was cracked, and the boot while being pliable still had cracks as well. I may just bite the $400 bullet and replace the remaining 7, along with new plugs as preventative maintenance.

 

[94SRUNNER]

Well, I replaced #7 this last weekend because it abruptly failed (threw the usual misfire code). I didn't pull the remaining 7 coils, but they all appear to be the same age (probably original w/ 300+k on them) and likely are a ticking time bomb. Looks like the PO from his records changed plugs out (80k miles ago now), but didn't replace any of the coils

Here is a few photos of the new DENSO vs old:
View attachment 2918354

View attachment 2918355

View attachment 2918357

The old coil tube was cracked, and the boot while being pliable still had cracks as well. I may just bite the $400 bullet and replace the remaining 7, along with new plugs as preventative maintenance.

It is worth inspecting them closely. Last year I had a shutter/stumble while the engine was warming up and the coolant was still below ~100*F. It went away once the engine warmed up. After research here on Mud, I decided to pull and inspect them. I found 2 were no-name units and the other 6 were OEM (likely original). The 2 no-name coils were discolored and had multiple cracks running down the length of the tube. I decided to install 8 brand new Denso units and the issue went away.

 

[DTCsk8er]

It is worth inspecting them closely. Last year I had a shutter/stumble while the engine was warming up and the coolant was still below ~100*F. It went away once the engine warmed up. After research here on Mud, I decided to pull and inspect them. I found 2 were no-name units and the other 6 were OEM (likely original). The 2 no-name coils were discolored and had multiple cracks running down the length of the tube. I decided to install 8 brand new Denso units and the issue went away.

Good point. I've read about the coil performance degrading just prior to hard failure, so it is possible that this is what I am seeing. I have also noticed my MPG is somewhat erratic in the last few months (had a few tanks below 10MPG, which is fairly rare for me, even with a lead foot and lots of city driving).

EDIT: This is pre-adjusted MPG... so add about 9-10% to this value due to larger tires to get the true MPG

- This is our daily driver, as well as trip vehicle; so the spikes into the 12-14 range are probably from when we do more HWY driving than usual.. but you can clearly see a somewhat downward trends since mid last year.
- An interesting stat from this app; Since I've been tracking it on this phone (2018), during the last 48 months, I've travelled 52k miles, and purchased 4328 gallons of gas ($10,130 USD total)

Just went ahead and ordered the remaining 7 DENSO coils and 8 new SK20R11 plugs. Let's see what happens!

 

[94SRUNNER]

@DTCsk8er I should also note, I had no CEL for the faulty coil packs.

Good idea to do plugs while you are in there. Make sure you get them torqued correctly, 15-17ft-lbs. There is a good thread that discussed this at length.

 

[medtro]

But the truck should build pressure when you key on

Not in stock configuration.

 

[BnvS]

Not in stock configuration.

Yeah I believe Toyota don't build fuel pressure with key on. They may build break pressure in the master cylinder on key on. Iirc.

 

[abuck99]

Good point. I've read about the coil performance degrading just prior to hard failure, so it is possible that this is what I am seeing. I have also noticed my MPG is somewhat erratic in the last few months (had a few tanks below 10MPG, which is fairly rare for me, even with a lead foot and lots of city driving).

View attachment 2918381

EDIT: This is pre-adjusted MPG... so add about 9-10% to this value due to larger tires to get the true MPG

- This is our daily driver, as well as trip vehicle; so the spikes into the 12-14 range are probably from when we do more HWY driving than usual.. but you can clearly see a somewhat downward trends since mid last year.
- An interesting stat from this app; Since I've been tracking it on this phone (2018), during the last 48 months, I've travelled 52k miles, and purchased 4328 gallons of gas ($10,130 USD total)

Just went ahead and ordered the remaining 7 DENSO coils and 8 new SK20R11 plugs. Let's see what happens!

Four thousand three hundred twenty eight gallons-

When you spell it out, you get your moneys worth

Here’s a 5,000 gallon tank for reference- the oil companies love Land Cruisers

I’m about the same fuel usage in the past 50k miles.

 

[BnvS]

I mean you gotta v8. Live happy with the choices you make. Would you rather drive a 4 cyl?.... Yeah didn't think so.

 

[flintknapper]

34 psi 15 minutes after shutdown is well within spec. FSM indicates fuel pressure should be above 21psi 5 minutes after shutdown (sorry, the picture cut off the 5 minute notation).

View attachment 2918310

In 2020 I spent a lot of time chasing what I thought was a fueling issue. The fuel pressure never really changed whether the FPR vacuum sensing hose was connected or not, even with a new FPR.

In regards to the stumbling when starting on a 'warm' engine, have you checked to see what your coolant temperature and mass air flow sensors are reporting when it sumbles?

Yep, his fuel pressure is fine.

You can make an adapter to attach a gauge like the OP did....or just install a permanent gauge (is what I did).

 

[Dusten]

Not in stock configuration.

That'll be the first rig Ive owned like that.
My 80 has mechanical injection so I don't have first hand experience.

 

[flintknapper]

The fuel pressure is usually maintained by a check valve in the pumps.

But the truck should build pressure when you key on so rails losing pressure while sitting shouldn't be an issue.

(U.S. Market Petrol engines) will not, do not 'prime' the fuel system with the key at the 'on' position. The fuel pump circuit is not energized until the engine is 'cranking'....at which time it pressures up the fuel rail.

 

[Dusten]

(U.S. Market Petrol engines) will not, do not 'prime' the fuel system with the key at the 'on' position. The fuel pump circuit is not energized until the engine is 'cranking'....at which time it pressures up the fuel rail.

Ya I was corrected a few posts up. That's kind of an odd feature. Almost all efi cars I work on build pressure at key on.

 

[flintknapper]

Ya I was corrected a few posts up. That's kind of an odd feature.

Safety feature.

Almost all efi cars I work on build pressure at key on.

Agreed. And this is the pretense for the arguments some folks pose when dealing with the 80-100 series Land Cruisers.

Not you, but you wouldn't believe how adamant certain people are about this lack of 'priming' feature. Because nearly all other manufacturers employ it (prime fuel system with key at on position) then it must be true of Toyota too they will argue.

I am not trying to labor the point....its just that not knowing this has led many, many folks to believe they have a fuel pump issue or other fuel delivery problem.

 

[DTCsk8er]

Yep, his fuel pressure is fine.

You can make an adapter to attach a gauge like the OP did....or just install a permanent gauge (is what I did).

View attachment 2918988
View attachment 2918989View attachment 2918990
View attachment 2918991
View attachment 2918994

Awesome idea! I wasn't thinking long term, but this may be a better option than spilling gas to hook up my gauges in work clothes.

 

[DTCsk8er]

I mean you gotta v8. Live happy with the choices you make. Would you rather drive a 4 cyl?.... Yeah didn't think so.

Thankfully I did not buy the landcruiser for her MPG, it just hurts to do the math of owning it. That being said, my 85 4runner got about 14mph with the 22re 4cyl (huge tires and not aerodynamic at all). Cruiser is a much more comfortable rig than that, and well worth the sacrifice for me!

Four thousand three hundred twenty eight gallons-

When you spell it out, you get your moneys worth

Here’s a 5,000 gallon tank for reference- the oil companies love Land Cruisers

View attachment 2918811

I’m about the same fuel usage in the past 50k miles.

LOL. It definitely makes it hurt more knowing I've used that much gas just lugging the kids around and going to work!