91 2LTE. Error code DTC-4 (engine coolant temp sensor) Troubleshooting (1 Viewer)

[Rosters]

Try to trouble shoot but do not have any diagnostic information (such as voltage) or manuals. Can anyone help?
I have been through the various threads in all forums here and explored attachments that had manuals or links.
Member GTSSportCoup was very helpful but sill no success No success. Can anyone provide direction?
Getting excessive white smoke on start. Been through just about every portion of the engine and cannot find the issue but the error code is new
The sordid history is in the 90s forum ("91 Prado Cold Start") if you want to share my pain
Thanks

 

[GTSSportCoupe]

The engine coolant temp sensor won't cause the sort of problems you're having I don't think. But it does cross over the north american coolant sensors; so is easy to replace. It's worth a try! Toyota part number for it is: 89422-35010 It's located under the intake manifold in the side of the engine block. Bit of a PITA to get at.

Can you make a point form list of all the work you've done to try to solve this problem? I'll review it and see if I have anymore suggestions.

 

[jmylie]

Dumb question, where did you get the error code from?

Is there a obdc connector?

 

[GTSSportCoupe]

Dumb question, where did you get the error code from?

Is there a obdc connector?

You jump a couple pins in the diagnostic connector, and the check engine light flashes codes. T1 to E1 or something like that. Only the electronic injection motors have this ability.

 

[Rosters]

The engine coolant temp sensor won't cause the sort of problems you're having I don't think. But it does cross over the north american coolant sensors; so is easy to replace. It's worth a try! Toyota part number for it is: 89422-35010 It's located under the intake manifold in the side of the engine block. Bit of a PITA to get at.

Can you make a point form list of all the work you've done to try to solve this problem? I'll review it and see if I have anymore suggestions.

yes good point.
I will make a list and post later this afternoon
thanks for the suggestion and effort, as always I am grateful for your help

 

[Rosters]

yes good point.
I will make a list and post later this afternoon
thanks for the suggestion and effort, as always I am grateful for your help

The engine coolant temp sensor won't cause the sort of problems you're having I don't think. But it does cross over the north american coolant sensors; so is easy to replace. It's worth a try! Toyota part number for it is: 89422-35010 It's located under the intake manifold in the side of the engine block. Bit of a PITA to get at.

Can you make a point form list of all the work you've done to try to solve this problem? I'll review it and see if I have anymore suggestions.

91 Prado 2LTE 66K miles. hard to start and large volume of white smoke (gas smell) on startup. Smoke disappears after 2-3 minutes of driving. Drives very well, no power loss. See video below of current level of smoke
Work to date
1. New head (1 month before I bought)
2. Replaced air and fuel filters
3. Engine thermostat replaced
4. Injectors rebuilt seals replaced. checked function 3 times.
5. Timing checked. ok
6. Fuel pump rebuilt and tested. ok
7. Fuel lines replaced- tested for air intrusion. ok
8. Cooling system tested for hydrocarbons. ok
9. Cylinder Compression test (1 -438, 2-360, 3-400, 4-395)
10. ECM tested. Ok
11. wiring harness tested. ok
12. engine run on nurse tank. no change in smoke issue
13. glow plugs tested twice. ok
14. EGR bypassed
15. pump timing checked. ok
16. two error codes DTC 5 (pump resistor) cleared. DTC 4 Engine coolant currently an issue.
17. Oil is clean, not overheating, good power.

 

[GTSSportCoupe]

Running through your list, even though compression is within factory spec, I think it could still cause these start issues. I had similar compression on a 2LTE in the past, and it would start almost that bad if it did not glow it three times.

So here's what I'd do:

First, measure voltage at your glow rail (to ground) at cold start when someone turns the key to 'on'. You should get 11V for ~7 seconds. If this is happening, your glow system is definitely working. Don't actually start the motor; just time the glow cycle to make sure it's the right period of time. At the 7 second mark, you should hear the glow relay open. Turn the key back off.

Once you're confident its working, do three glow cycles in a row. Turn key to 'on', wait 7 seconds for relay to open. Turn key back to off for about 2 seconds. And repeat. Do this three times. Then start the motor. Does it start cleaner?

Once my old low compression 2LTE was warmed up it ran fine and had decent power. Tons of blow-by from the bad compression though. So, one other test you could do to see if your compression problem is the bottom end, is remove the oil filler cap with the engine running, and set it back on the hole. If it bounces around a bit, your blowby is normal. If it flies right off; you've got problems.

One last thing. You say you removed your EGR system, but did you remove the throttle plates in the throttle body? If the EGR system is partially failed, and these are fully closed at startup, it'll starve the motor of air and cause this problem.

 

[Rosters]

91 Prado 2LTE 66K miles. hard to start and large volume of white smoke (gas smell) on startup. Smoke disappears after 2-3 minutes of driving. Drives very well, no power loss. See video below of current level of smoke
Work to date
1. New head (1 month before I bought)
2. Replaced air and fuel filters
3. Engine thermostat replaced
4. Injectors rebuilt seals replaced. checked function 3 times.
5. Timing checked. ok
6. Fuel pump rebuilt and tested. ok
7. Fuel lines replaced- tested for air intrusion. ok
8. Cooling system tested for hydrocarbons. ok
9. Cylinder Compression test (1 -438, 2-360, 3-400, 4-395)
10. ECM tested. Ok
11. wiring harness tested. ok
12. engine run on nurse tank. no change in smoke issue
13. glow plugs tested twice. ok
14. EGR bypassed
15. pump timing checked. ok
16. two error codes DTC 5 (pump resistor) cleared. DTC 4 Engine coolant currently an issue.
17. Oil is clean, not overheating, good power.

Running through your list, even though compression is within factory spec, I think it could still cause these start issues. I had similar compression on a 2LTE in the past, and it would start almost that bad if it did not glow it three times.

So here's what I'd do:

First, measure voltage at your glow rail (to ground) at cold start when someone turns the key to 'on'. You should get 11V for ~7 seconds. If this is happening, your glow system is definitely working. Don't actually start the motor; just time the glow cycle to make sure it's the right period of time. At the 7 second mark, you should hear the glow relay open. Turn the key back off.

Once you're confident its working, do three glow cycles in a row. Turn key to 'on', wait 7 seconds for relay to open. Turn key back to off for about 2 seconds. And repeat. Do this three times. Then start the motor. Does it start cleaner?

Once my old low compression 2LTE was warmed up it ran fine and had decent power. Tons of blow-by from the bad compression though. So, one other test you could do to see if your compression problem is the bottom end, is remove the oil filler cap with the engine running, and set it back on the hole. If it bounces around a bit, your blowby is normal. If it flies right off; you've got problems.

One last thing. You say you removed your EGR system, but did you remove the throttle plates in the throttle body? If the EGR system is partially failed, and these are fully closed at startup, it'll starve the motor of air and cause this problem.

very good
will go ahead and run the above tests today
will report back
Best

 

[Rosters]

ok did the above testing which then led to my mechanic isolating cylinder #2 (low compression) . Cold start, Bingo! no smoke. repeated the test several times. Looks like the head has to come off. Fuel delivery route is now off the table. hopefully we get the head off, reviwed and machined next week.

 

[GTSSportCoupe]

ok did the above testing which then led to my mechanic isolating cylinder #2 (low compression) . Cold start, Bingo! no smoke. repeated the test several times. Looks like the head has to come off. Fuel delivery route is now off the table. hopefully we get the head off, reviwed and machined next week.

I'm glad to hear you're getting somewhere with it. So you're saying that doing multiple glow cycles got you a clean startup?

Sadly when the cylinder heads crack on these, water/coolant can sit in the cylinder bores if the problem is not dealt with quickly. This can rust and pit the cylinder bore; causing bad compression. This is how my LJ78 came to me. I lived with it for a few years, and eventually swapped out the short block for a known used good one. It was a lot of work, but made such a huge difference at start up.

 

[Rosters]

sorry I was offline for a few days
To clarify, the multi glow cycles did not produce much difference in smoke issues. My mechanic (for reasons unknown) isolated the low compression cylinder and the engine started and ran without any smoke. Head is now off, pics attached. I'm far from the expert on this but am told the majority of the valves are leaking with some damage to cylinder (top) of walls. Who ever carried out several months ago (before I bought it) would have seen this so its disappointing. in any event, I need to move forward with repairs.

 

[GTSSportCoupe]

That pitting is what happens when someone runs a cracked head for too long. The coolant/water leaking in causes the pitting. As horrible as it looks, the pitting at the top of the cylinder bores is probably not what is causing your compression problems. It's more likely the rings of rust in the cylinder bores. My first short block was damaged in much the same way. I replaced it with another one that had good compression.

Anyhow, I'd say you're either looking at over-boring and rebuilding that block, or doing an engine swap of some sort.

Is that cylinder head OEM Toyota, or an off shore one?

I recently uploaded an album of me correcting this same problem a couple of years ago for my truck: 2LTE semi-rebuild

 

[Rosters]

That pitting is what happens when someone runs a cracked head for too long. The coolant/water leaking in causes the pitting. As horrible as it looks, the pitting at the top of the cylinder bores is probably not what is causing your compression problems. It's more likely the rings of rust in the cylinder bores. My first short block was damaged in much the same way. I replaced it with another one that had good compression.

Anyhow, I'd say you're either looking at over-boring and rebuilding that block, or doing an engine swap of some sort.

Is that cylinder head OEM Toyota, or an off shore one?

I recently uploaded an album of me correcting this same problem a couple of years ago for my truck: 2LTE semi-rebuild

just a note to say thanks for all your help. I finally got the head repaired. Just a little smoke on start but mostly eliminated. Drives very well.
BTW: I did some spring cleaning and have several old parts (from my 71FJ40) that I was going to post in the classifieds. Not looking to make any money, some of the parts are beat up but wanted to at least see if I could help others on the forum. Would like to give you first dibs by way of thanks.

 

[GTSSportCoupe]

just a note to say thanks for all your help. I finally got the head repaired. Just a little smoke on start but mostly eliminated. Drives very well.
BTW: I did some spring cleaning and have several old parts (from my 71FJ40) that I was going to post in the classifieds. Not looking to make any money, some of the parts are beat up but wanted to at least see if I could help others on the forum. Would like to give you first dibs by way of thanks.

Hi @Rosters ; that is very kind of you! I'm not in need of anything, but I certainly appreciate your thankfulness! I'm sure there are some other fellows out there who'd be happy to have some 40 parts.

Glad to hear it runs better now! I ran my first block for years just fine with similar cylinder bores to yours. It never got any worse. Downsides were minor with a little bit of smoke on start up and a little above average blow-by and oil loss. I think you made a good call keeping the short block for now. Good luck with it.