Hesitation / no power when engine compartment is hot (1 Viewer)

[Malleus]

I don't know how that could help the engine stumbling problem. The fuel rail and the fuel pressure regulator are cold by virtue of the fuel in them. Put your hand on either while the engine is running. I think it's more likely your leaf blower is doing the same thing your driving is: cooling the radiator.

You can try something similar: get a 1-gallon garden sprayer and fill it with water. The next time the engine stumbles, spray the radiator and see if it improves. If it does, your fan clutch needs new oil:

Much cheaper than a new fan clutch. Amazon will get it to you tomorrow. The whole job takes less than an hour.
Fan clutch mod, Post #1-5
See post #1

Did you test your thermostat? If you didn't you can't know whether that was actually a problem.

I'm still betting on the fan clutch.

 

[OrangeCrusher]

The fuel rail and the fuel pressure regulator are cold by virtue of the fuel in them. Put your hand on either while the engine is running.

This comment of yours is more helpful than you probably could imagine!

The fuel rail is so hot it burns my hands when I touch it with the engine running.

I've just disconnected the fuel hose from the fuel pressure regulator - dry! Nothing coming out.

I'll be taking off the FPR now and measure the pressure in the rail - if it's too low, it's the pump, if it's too high, it's the FPR?

 

[OrangeCrusher]

12 psi - way too low! I'm surprised it runs at all with this?

In addition, I also tried to done some quick testing of the FPR with compressed air. I tried up to 70psi, and nothing came out. Does it need liquid to operate / open?

 

[blinkerfluid]

View attachment 3744722

12 psi - way too low! I'm surprised it runs at all with this?

In addition, I also tried to done some quick testing of the FPR with compressed air. I tried up to 70psi, and nothing came out. Does it need liquid to operate / open?

FPR should release air around 40-50 psi, replace both the FPR and fuel pump, check all fuel lines solid and soft while you're at it.

 

[Malleus]

I'd test the fuel pressure regulator before I bought a new one.

 

[Malleus]

 

[Malleus]

 

[OrangeCrusher]

I have ordered a fuel pump and FPR. Both should arrive by Thursday and I'll report if it's solved.

I'm highly optimistic that it will be solved with this as all the symptoms seem to be perfectly explained with vapor lock occurring in the fuel rail due to lack of circulation.

The low fuel pressure explains another VAF related issue - the spring in the VAF is turned pretty much all the way down in the "loose" direction to make it run reasonably. I now assume this is to make the ECU think there is more air coming than there actual is, to make it open the injectors longer to compensate for the low fuel pressure.

Not that it really matters but I also wondered how it could be that the fuel pump incl. strainer etc appeared so new when I looked at it the other day (I had to take it out bc the gasket between the tank / fuel pump bracket was missing and fuel leaking out when filling it up). My hypothesis is that the previous owner put an incorrect fuel pump in there, one that produces lower pressures meant for carburetors.

 

[blinkerfluid]

Also check

I have ordered a fuel pump and FPR. Both should arrive by Thursday and I'll report if it's solved.

I'm highly optimistic that it will be solved with this as all the symptoms seem to be perfectly explained with vapor lock occurring in the fuel rail due to lack of circulation.

The low fuel pressure explains another VAF related issue - the spring in the VAF is turned pretty much all the way down in the "loose" direction to make it run reasonably. I now assume this is to make the ECU think there is more air coming than there actual is, to make it open the injectors longer to compensate for the low fuel pressure.

Not that it really matters but I also wondered how it could be that the fuel pump incl. strainer etc appeared so new when I looked at it the other day (I had to take it out bc the gasket between the tank / fuel pump bracket was missing and fuel leaking out when filling it up). My hypothesis is that the previous owner put an incorrect fuel pump in there, one that produces lower pressures meant for carburetors.

Also check power to the fuel pump, make sure it gets good voltage and wiring is OK.

 

[Malleus]

How is this going to fix the high operating temperature problem?

 

[OrangeCrusher]

@Malleus I currently believe that changing the thermostat has solved the higher than normal operating temperature. When I test drove it after the thermostat change, the ECT was circa 10 degrees C lower than before (88C instead of 97C before).
Maybe you can help me understand: Is 88C or 190F considered a "normal" operating coolant temperature? I understand it is slightly higher than the opening stamped into the thermostat (82C), but I was thinking this is probably within the tolerances.

 

[Malleus]

The normal operating engine coolant temperature is not the same as the thermostat opening temperature. Did you actually test the old thermostat? You need to know whether it was opening and at what temperature, if it was.

How do you know what the engine coolant temperature actually is?

 

[OrangeCrusher]

How do you know what the engine coolant temperature actually is?

1. I have the ECT readings shared above
2. I have confirmed the validity of the ECT readings via the the following ways:
a) measuring the temperature of the cooling system with an IR camera. I shared some of the images in the thread earlier. I also previously compared the IR camera readings to a physical temperature sensor, and at long as the surface was matte / non-reflecting, the measurements matched within 2 degrees
b) observing the ECT after the engine had cooled down for 24h. It matched the outside temperature within 1 degree.

I have not directly tested the old thermostat as I neither see the need to do so, nor do I have good equipment available to perform the test accurately.

 

[OrangeCrusher]

To clarify, I have retrieved the ECT readings using the Toyobd1 bluetooth adapter and android app.

 

[CharlieS]

You mentioned the VAF spring being set loose. I thought touching anything in the VAF was basically forbidden due to the risk of damage?

 

[OrangeCrusher]

I think "not touching anything in the VAF" is a great rule as long as your engine is running fine and you have no reason to believe there be an issue with the VAF.

In my case, the engine ran like crap or not at all, and a cursory inspection of the VAF showed that it was sometimes mechanically getting stuck. Disassembly then revealed that it showed signs of water ingress and corrosion.
At that point I had nothing to loose and have entirely disassembled, cleaned, readjusted the VAF. And my observation was that the only way the engine ran reasonably well was with the clockspring so loose that if you loosen it a quarter turn further, the fuel pump switch doesn't even click into the ofd position anymore.

 

[jpoole]

I'm reading through this quickly but it seems like you may be skipping some troubleshooting steps and being quick with the parts cannon. Of course, more is happening on your end than is in this thread and I didn't read every word so I may be wrong in that assessment.

Have you worked through the pages that @Malleus shared above? Did you confirm that the primary fuel filter is not the issue? Have you confirmed sufficient voltage at the pump during all operating modes?

You did mention that the fuel pump looks new so replacing it seems like it may be premature if you haven't ruled out low voltage or a clogged primary filter.

If fuel pressure is low it seems less likely to be the regulator and more likely to be an issue on the supply side.

Keep in mind that resistance increases in electrical circuits as heat of the components/wiring rises. How this may be impacting your 80 could vary and it may or may not be relevant to your low-power scenario but it also could explain why your performance issues are temp related. etc.

I've followed along as a friend of mine dealt with a very similar issue on a '94 that ended up being the result of multiple wiring issues causing intermittent or weak connections. It took a really long time for him to resolve the issues in part because of jumping into parts replacement and making things more complicated by changing too many variables. Consider using a multi-meter to monitor voltages at the pump during normal/good operation and poor performance scenarios. Use the ground that the pump is using in your tests, since it's just as essential as adequate power.

Good luck, hopefully it's a single problem and you find it soon.

 

[Malleus]

1. I have the ECT readings shared above
2. I have confirmed the validity of the ECT readings via the the following ways:
a) measuring the temperature of the cooling system with an IR camera. I shared some of the images in the thread earlier. I also previously compared the IR camera readings to a physical temperature sensor, and at long as the surface was matte / non-reflecting, the measurements matched within 2 degrees
b) observing the ECT after the engine had cooled down for 24h. It matched the outside temperature within 1 degree.

I have not directly tested the old thermostat as I neither see the need to do so, nor do I have good equipment available to perform the test accurately.

Good equipment? IT takes a stovetop, a pan of water and a candy thermometer.

 

[jpoole]

clockspring so loose that if you loosen it a quarter turn further, the fuel pump switch doesn't even click into the ofd position anymore

Do you think this is related to your low fuel pressure? Loosening the spring is allowing the AFM to open more for a given airflow and thus richening the fuel mixture. I've successfully tuned AFMs and it can be a great thing to do but you need to have all other tuning variables and system components dialed in and nailed down first in my opinion. I also prefer to have real time air fuel ratio available and to understand how the computer will compensate/adjust for tuning, etc.

If I understand where things are now you may need to retune your AFM once you fix your low fuel pressure issues.

Do you have fuel pressure numbers across a range of operating temps/conditions and are they consistently low or only low at high temps?

 

[OrangeCrusher]

@jpoole
1. I think the loose clockspring is a result of adaptation to the low fuel pressure, and I agree with you that I expect to have to readjust it once the low fuel pressure is fixed.
2. I have measured the fuel pressure with a hot and a partly cooled down engine. I have measured it with an idling and a stopped engine. I have also actuated the VAF fuel pump switch to change the pump speed. The fuel pressure was always exactly 12psi, that's why I feel it is the fuel pump (not the fuel filter bc this occurs without any fuel flow, not a voltage issue because the VAF fuel pump switch doesn't impact the fuel pressure - I can hear the pump change tone though / turn faster)

3. Yes I may be jumping to the parts cannon. However within reason, I prefer buying a few more parts than spending many hours trying to conclusively prove that a rather affordable part is definitely damaged. This is because a) I don't have infinite time, b) I'm getting itchy to drive this vehicle after owning it for nearly 3 months and only fixing / diagnosing things, c) I do have spent more than 100 hours diagnosing, repairing, driving the vehicle now and am not able to write down all the cues that I collected during that in the thread here.
- I also should write a general intro here but long story short, my cruiser has no rust on frame and body which is great, but it does look like the previous owners have neglected maintenance of the engine / suspension etc, and pretty much everything that I have touched is either a) crumbling (hoses, connectors, etc), b) incorrectly put together (under torqued, over torqued, dangling around, etc pp). My long term goal is to maintain this cruiser and bring it back into great condition, for which I believe the basis is there given the rust free condition. Hence my bias is to buy a new part if I see something that is in questionable condition and likely to break in the near term, even if it is not broken yet.


@Malleus I actually do not have a candy thermostat, but thanks to your insisting and to comply with your nudge to test the old thermostat, I am going to buy one now and perform the test Another obstacle could be that I'm at 5000ft, which means the water may boil before the potentially broken thermostat - but we will see!