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

[OrangeCrusher]

Hello!

I have a 1993 FZJ 80 (US spec)that has the below issue. Would appreciate some input as I feel like I'm getting stuck with this

The issue appears to be correlated with heat in the engine compartment. It does not happen when going high speeds at high power (e.g. going up a long incline at full power and 70mph at 100degF is fine), but it does happen under following situations:

• parking it in the sun / heat after a drive, and then trying to restart it again within an hour
• rockcrawling / going slowly offroad in the heat for prolonged periods of time

It can happen at the most inopportune moments, and can be fixed with shutting the engine off, opening the hood, and waiting

Symptoms / what then happens is:

• rough idle
• hesitation / very poor throttle response. Initially only at low rpm (<1800rpm), but if it progresses also at higher rpm. It eventually get's so bad that you basically can't move it, or it just stalls

It appears to be a fuel / injection / mixture issue. When this happens, I can fix it by spraying brake clean in the air intake, and it immediately recovers. Or I can manually move the VAF towards "more air coming in", and it recovers as well - up to a point. If it gets worse, eventually the VAF manipulation doesn't work anymore and also a rhythmic misfire develops (so, instead of some cylinders misfiring randomly, always the same cylinder(s) misfires). I don't know for sure which cylinder it is, but I noticed that if I remove the injector 1 connector, the engine sounds still exactly the same. I wasn't yet able to try this with the other injectors as those are harder to access.

What has been done so far:

• previous owner replaced the spark plugs and wires, they're basically brand new (Denso plugs / NGK wires)
• previous owner appears to have replaced the fuel pump (the entire pump / filter / level sender unit looked brand new)
• I replaced the injectors with refurbished and flow tested Denso injectors
• I replaced the valve cover gasket (was leaking), fixed broken valve cover bolts, and adjusted valve clearance on 3 exhaust valves which was out of spec (too tight)
• I replaced the IAC (had no stable idle before, now idle is fine unless above condition occurs)
• I replaced most of the vacuum hoses and did a smoke test - there is only a very small leak from the IAC which I don't think can cause this. It's because I forgot to order a new gasket for this, will replace that gasket as well.
• I took the VAF apart and cleaned it etc, as it was initially sometimes getting stuck. Previous owner has taken it through deep water I think, the VAF internals were somewhat corroded. It's not perfect now, but it's moving freely and all resistance values within spec according to FSM. The VAF does not appear to be OE, but a China copy. Would love to buy a new / used OE one, but can't fine one. I bought another China copy, but that one appears to be even worse - engine doesn't run straight at all with it.
• checked timing

I bought the rig three months ago in non-running condition (bad starter + all of the above), and have no specific idea about the history, or when this specific issue started.

My analysis:
It's not a fuel supply issue (clearly getting enough fuel running at high power). It could be ignition related, but unlikely given a lot of that has been renewed AND it is clearly running lean / reacting positively to additional fuel.
Hence it's gotta have something to do with the fuel injection. As I already replaced the injectors, what remains is:

1. Wiring harness
2. ECU
3. other sensors that ECU listens to determine injection quantity (which?)

Even though I can't see anything specifically wrong with the wiring harness ( it is not visibly melted at the EGR pipe location), it appears to be in generally poor condition and my bet is on this as the cause.

Plan:
I have ordered new injector connectors, wire, shrink butt connectors and plan to replace at least the injector part of the harness. I read some hints that folks have done this before - can someone give me a hint where to start? Should I go all the way back to the ECU connector and pull new wires from there? Or splice into the existing harness in the engine compartment (before the heat exposed EGR pipe location)?

If anyone has any other hints on what to try, I'd really appreciate that! Thanks!

 

[Irish Reiver]

Have you checked for any codes? Also worth checking the temp sensor in the head that feeds the ECU (not the dash guage). Having a Toyocom ECU reader would be a good help here.

 

[blinkerfluid]

I'd check the fuel EVAP system, its solenoid is wedged b/w the intake manifold IIRC and the canister is right besides the battery. canister has a one way valve if I remember correctly - check that system, it may be causing a vapor lock / high pressure inside the fuel tank situation. Have you tried removing the gas cap when this happens?

 

[Malleus]

You didn't mention that the check engine light (MIL) was lit, so I assume you checked and there are no engine fault codes.

Since you state that this only happens when the engine is hot, why isn't that the first place to look?

The numbers on the troubleshooting matrix are the order in which to inspect that potential symptom. Items 1 and 2 are oil leak and fuel quality, respectively. Since you didn't mention any significant oil leak and since we don't regularly mix sand in our gas (as some countries do), the ECT (EG-243) is the first place to start.

Since the problem doesn't happen when the engine is at normal operating temperature, your problem description is "engine compartment is hot", my guess is that the fan clutch isn't working properly. You should still verify there are no problems with the ECT circuit, but draining the clutch and refilling with heavier oil would be a good thing to do, since you don't know the history of the truck.

The ECT circuit inspection procedure is on pg EG-299, but since the engine runs fine unless it's hot, I would suspect that circuit and the sensor are working properly.

ECM voltage values are listed on ppg EG-234. The complete fuel system (SFI) troubleshooting procedure is on ppg EG-218 to EG-320.

The engine coolant temperature (ECT) circuit controls the fuel cut rpm and the circuit opening relay. This is described in the service manual (EG-320). If you don't have one, you can download it for free from the Resources section.

FWIW, there are 20 items on the list; "fuel injector" isn't one of them. If you're not convinced that this is the correct procedure to follow, you can verify the injector voltage during idling 9-14 VDC (pg EG-241). If it falls below this range, there is a problem in the injector circuit.

 

[Malleus]

There is another possibility, related to the hot operation. The A/C circuit is designed to shut off when the engine exceeds the temperature setpoint. If this circuit, or its sensor, isn't operating properly, it can adversely affect the normal engine operation. The inspection and repair procedures for that circuit are also in the service manual, but I would only look there after checking the 20 items in the troubleshooting matrix off the list.

The last thing I would do is to try to rewire the injector circuits. But that's just me.

If I was inclined to do that, I wouldn't splice butt connected wires into the existing terminals, after I replaced the connector housings, though. I'd crimp new terminals onto the new wires and stuff them into the new connector housings. Ballenger Motorsports has new terminals, connector housings and housing seals, from Sumitomo, for much less than Toyota sells them. The wiring harness repair manual list all the relevant information; it's also in the Resources section.

 

[Malleus]

For a little background, the ECT sensor is an input to the VAF (you can see this on the circuit diagram, pg EG-206). The VAF directly controls the circuit opening relay, which in turns controls the fuel pump, through the fuel pump relay and fuel pump resistor.

I suspected this was the root cause of the problem, since you mentioned spraying brake clean into the air intake, which means you're modifying the VAF air input to the control system.

You also mentioned you have an aftermarket VAF, which could be a problem, but I suspect isn't the cause of the "hot engine" operation fault. If I had to spend money. it'd be on a replacement VAF. Contact @slow95z.

 

[OrangeCrusher]

Wow - so many helpful response so quickly! Thanks!

To clarify a few questions:

1. CEL is not on. I have not recently read codes (can it have codes without the lamp on?)
2. There is no pressure building in the tank.
   1. The previous owner had disconnected the EVAP system (the two hoses connecting the canister to the vacuum circuitry below the intake manifold had been pulled off). I reconnected it (after replacing all the old brittle vacuum hoses below the intake), but haven't specifically tested if it's working correctly now. Also, the hose from the tank to the canister looks pretty rotten - it's most likely leaking somewhere. It's definitely on my list to replace, but I don't think enough air could be sucked in through this small hose to cause the severity of the symptoms. I also tried pulling off the hose to the tank at the canister and blocking the canister inlet with my finger - that did not change the poor running condition.
3. When this happens, the coolant temperature indicator in the dash is showing normal operating temperature. So it is not "overheating" in the conventional sense.
   1. I have seen the dash coolant temperature go to an elevated indication (say 75% up). This was while going up one of the steep canyons here in Utah on the Interstate, at 70mph and pretty much full engine power (full throttle, 4,000rpm) and 90degrees outside. Everything was working fine then. So I don't have indication that the coolant temperature per se is correlated with the symptoms.
   2. The fan is not obviously dysfunctional (it is running and pushing through air. No idea if it should be more though?)
4. The A/C is out of order currently bc of a leak, and has not been on during any of the test drives related to this issue.

Malleus - thanks for the pointer on the ECT and the FSM troubleshooting procedure in general! I have to admit that I have not followed that yet. I will look at this today and report back!

 

[OrangeCrusher]

One additional symptom that appeared yesterday:
Towards the end of a 4 hour offroad trip that was driven entirely in low range, and during which the issue above persisted the majority of the time, the "diff lock" indicator in the dash came on for the first time. I had never seen this indicator light up in this rig before. It was flashing on / off with an inconsistent pattern, and did not stop doing so even when I switched back into high range and driving for miles on a gravel road. (The 1993 version doesn't have a separate switch for the center diff lock. This rig has no front / rear lockers).

I think it's probably another wiring issue, but probably not directly related to this?

Btw the reason I think it's a wiring issue: Pretty much all wiring / connectors down there seems rotten. E.g. I replaced the transmission position / NSS wiring earlier this week (no gear indication in the dash before). The connector was very corroded inside, some of the wires fell out of the connector, and the wires looked like they had water in them at some point (copper strains not shiny but black/green/dull).

 

[slow95z]

I haven't had a vfm in years, I get one and it's sold that day. Sorry man but that's a damn near impossible part to find

 

[Malleus]

Wow - so many helpful response so quickly! Thanks!

To clarify a few questions:

1. CEL is not on. I have not recently read codes (can it have codes without the lamp on?)
2. There is no pressure building in the tank.
   1. The previous owner had disconnected the EVAP system (the two hoses connecting the canister to the vacuum circuitry below the intake manifold had been pulled off). I reconnected it (after replacing all the old brittle vacuum hoses below the intake), but haven't specifically tested if it's working correctly now. Also, the hose from the tank to the canister looks pretty rotten - it's most likely leaking somewhere. It's definitely on my list to replace, but I don't think enough air could be sucked in through this small hose to cause the severity of the symptoms. I also tried pulling off the hose to the tank at the canister and blocking the canister inlet with my finger - that did not change the poor running condition.
3. When this happens, the coolant temperature indicator in the dash is showing normal operating temperature. So it is not "overheating" in the conventional sense.
   1. I have seen the dash coolant temperature go to an elevated indication (say 75% up). This was while going up one of the steep canyons here in Utah on the Interstate, at 70mph and pretty much full engine power (full throttle, 4,000rpm) and 90degrees outside. Everything was working fine then. So I don't have indication that the coolant temperature per se is correlated with the symptoms.
   2. The fan is not obviously dysfunctional (it is running and pushing through air. No idea if it should be more though?)
4. The A/C is out of order currently bc of a leak, and has not been on during any of the test drives related to this issue.

Malleus - thanks for the pointer on the ECT and the FSM troubleshooting procedure in general! I have to admit that I have not followed that yet. I will look at this today and report back!

1. Yes the codes are stored in the ECM. It doesn't care if the light works or not. Does it come on when the key is on, before the engine is started?

2. By "the tank" do you mean the fuel tank? It should not have any pressure in it. BTW, I don't believe your problem is a fuel delivery problem, per se. I think fuel delivery is a symptom of the problem.

3. The engine temperature gauge is all but useless. It is correct twice: when the engine is cold and after it's overheated. Toyota designed it that way to keep people from annoying the dealers when the engine temperature rose near the setpoint. If you want it to work, see @RavenTai's gauge modification. The 3rd generation OBDII folks can use a Bluetooth reader to get the engine coolant temperature, but the '93 and '94 models don't have that luxury.

4. Whether the A/C works or not is irrelevant; the circuit still works because the sensor is still in the head and still connected to the ECM.

 

[Malleus]

One additional symptom that appeared yesterday:
Towards the end of a 4 hour offroad trip that was driven entirely in low range, and during which the issue above persisted the majority of the time, the "diff lock" indicator in the dash came on for the first time. I had never seen this indicator light up in this rig before. It was flashing on / off with an inconsistent pattern, and did not stop doing so even when I switched back into high range and driving for miles on a gravel road. (The 1993 version doesn't have a separate switch for the center diff lock. This rig has no front / rear lockers).

I think it's probably another wiring issue, but probably not directly related to this?

Btw the reason I think it's a wiring issue: Pretty much all wiring / connectors down there seems rotten. E.g. I replaced the transmission position / NSS wiring earlier this week (no gear indication in the dash before). The connector was very corroded inside, some of the wires fell out of the connector, and the wires looked like they had water in them at some point (copper strains not shiny but black/green/dull).

It's probably a loose connection at the transfer case. Unless it's a problem with the combination meter display.

 

[OrangeCrusher]

For a little background, the ECT sensor is an input to the VAF (you can see this on the circuit diagram, pg EG-206).

@Malleus Thanks for referencing this circuit diagram!

I'm not seeing the ECT sensor as an input to the VAF, though.

As I understand it:
THA - Temperature Air
VC - Voltage constant (just measured, 5V)
VS - Voltage output of the air flow sensor (just measured, circa 1.6V at idle - I guess it will fluctuate with the sawtooth pattern)
E2 - Earth 2?
FC - Fuel control?
E1 - Earth 1?

And then further in the diagram for the ECT:

THW - Temperature water?
E2 - Earth 2 (shared with the VAF temperature, and the EGR gas sensor - California only)

 

[Malleus]

The VAF, ECT and EGR gas inputs are tied together at E2, and connected to the ECM. This grounds the circuit.

 

[OrangeCrusher]

I realized I had actually ordered an OBD1 bluetooth reader (Toyobd1), but never installed it. I hooked it up today and took it for a drive. After the drive I let it idle, and within a few minutes the issue occured.

I recorded it on the video here:

Few comments:

1. As far as I can tell, the rich / lean label in the app is inverted. The oxygen sensors are actually stuck lean when the app shows them as stuck rich (outputting <0.1V, measured with voltmeter earlier today)
2. The ECT temperature showed reasonable values throughout the day. All the way from warm up, to straight driving (typically at 93-97degC - a bit high but not unreasonable)?, and up to 103degC when climbing a rather steep section of interstate. I don't know if it's a good comparison, but my other car (BMW X5 Diesel) shows pretty much the exact same coolant temperature profile across this drive, including the elevated temperature during the climb.
3. I drove it for about 60 miles before this, including an elevation gain of >3000ft in there. So it definitely had to some work, and had no issues while driving
4. The issue visible here is not purely restricted to idling. Throttle response is also very poor to the extent that often you can't get it moving at all.

 

[Malleus]

Two things:
1) 93°C =199°F, which is too high for "normal" driving. I don't know what "straight" diving is. Speed and outside air temperature, and whether the A/C system was on or not (I know you mentioned yours didn't work), are the variables that are required to make an accurate assessment of the cooling system, but I think your clutch is not working properly.

You shouldn't see more than 185°F (or 85°C) during around town, stop and go driving, with ambient air below 90°F. Normal idling temperature should be around 176°F (80°C). It should be less at highway speeds. This is what a properly working cooling system should do; you'll get a wide variety of "real world" experience with other temperatures.

I don't remember you mentioning whether or not you have verified that your thermostat is working properly. Also, the ECT sensor has to be validated; the procedure is on page EG-299.

I have a '95 with a one year old head (and a very clean cooling system and new fan clutch), and 300k on it and another '95 with the original head on it and 230k on it. Neither operate above 185°F. Granted, I'm at 300-ft MSL, however, the refreshed head engine made it to the eastern continental divide and back soon after it as installed, in the summer, and performed similarly. I also have a '94, with 300k on it, that performs similarly, with OEM parts.

2) I take "idling" in the troubleshooting matrix to include steady state operation, since no other steady state operation is listed, and this is obviously a potential fault condition.

Also, I included the EGR gas temperature sensor circuit because you never stated whether or not your 80 was a California model or not. It's really irrelevant; the 3rd generation 80s all have the EGR gas temperature sensor in them, and the logic is the same.

 

[Malleus]

While you're at it, you can (easily) verify the ignition coil operation (IG-16) and the distributor operation (IG-17), just to rule those out. I don't remember you mentioning that the coil and/or distributor had been replaced or verified. Both can be subject to faults at high temperatures, but neither would cause a high engine operating temperature.

For the purpose of identifying operating conditions with respect to the service manual, these are the definitions used:
"Cold" engine is -10°C (14°F) to 50°C (122°F)
"Hot" engine is from 50°C (122°F) to 100°C (212°F)
The thermostat opens at about 180°F (between 176° and 183°F).

 

[OrangeCrusher]

Interesting on the coolant temperature, thanks @Malleus !
I didn't realize it should be 80C / 180F, that's quite a difference. This morning, after a short drive, the ECT reads the same temperature as yesterday (93-97C), even though it is much colder outside. So because the temperature appears to be elevated constantly, I think it has to do with the thermostat rather than the fan.
I know it's not always accurate, but I quickly measured the temperature with an IR camera this morning, and it reads the same as the ECT (about 93C).

So based on that I have ordered a thermostat. Would be great if it's only that!

 

[OrangeCrusher]

Thermostat bypass pipe - 93C
Radiator return hose - ~20C

 

[Malleus]

If it's stuck closed, that'll cause problems, for sure.

 

[OrangeCrusher]

I was able to source the thermostat (Aisin) and gasket locally, and put it in this afternoon. The replacement was about the easiest job ever - so accessible! The old thermostat appeared to be of the same type, also had 82degC opening temp stamped into it. There was a bit of gunk on it but nothing dramatic.

It's a partial success - it's running circa 10degC cooler now (typically 88C instead of 97C before).

However - the rough running issue is still there In exactly the same way as described above. Got nearly stuck at the grocery store, and then it started again with 3 minutes of idling once I got home.

The only additional things I learned:

• I can stop / reverse the situation by blowing air on the fuel rail pane (from the front aiming between the cylinder head and the intake manifold) using a leaf blower. I assume that cools whatever is heat affected
• the situation also rapidly improves if I can get it driving - I assume the headwind has the same effect as the leaf blower.

I think I'm done with this today and get back to it tomorrow