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1997 T100 RWD Auto
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72 Posts
Discussion Starter #1
I sort of delved into this issue a little on my head-gasket job thread:
https://www.toyotanation.com/threads/replacing-single-head-gasket.1659842/

But I felt like I should start a new thread, since this problem is (I do not think) related to me changing head-gaskets.

The problem:

If I clear all codes and drive for roughly 20 miles or so, I will get a CEL with code P0301 (misfire on 1).
I can repeat this and it will always happen t he same way. I currently do not have a gauge where I can see real-time (but it is on my get-list).

So far, I have:

Swapped plugs, coil, and injector with 3...same result..problem did not move over to 3. I also used new o-rings when moving the injectors.
Checked for vacuum leaks using carb-cleaner. This method helped me find all the cracked vacuum hoses I had (and replaced). It is not showing any more vacuum leaks.
Cleaned MAF and throttle body.
Cleaned all grounds (including the brown grounds by the diagnostic port)

My guesses as to what might be causing this are:
semi-broken wire on the harness that breaks the circuit during driving ?
..or
I noticed that injector 1 does not seem as tight as the other injectors. I can wiggle it a little more freely than 3 and 5. Could my fuel-rail be slightly bent upwards on the end with injector ...so it is not tightening down as much as the other injectors....


Any other hunches? I read one post where a guy found a nick on the tone-ring of his crankshaft, which caused a random misfire. I might pull that lower cover off so I can look at it just to rule that out, but that seems like an obsure thing to happen.
 

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'97 TC & '97 T-100
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246 Posts
Sounds like a PITA...

Well, Bam already suggested to check grounds on the intake by connector. There is one more on the back side of the intake that held by small screw that you have to use stubby to screw in.

There is also another test I would probably do - cylinder leak down. Tool is readily available in Harbor Freight for 30 bucks. (link below)


Other than that... maybe pull up wiring manual and check continuity and short to ground of wires going to #1 injector.
 

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1997 T100 RWD Auto
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72 Posts
Discussion Starter #3
T
Sounds like a PITA...

Well, Bam already suggested to check grounds on the intake by connector. There is one more on the back side of the intake that held by small screw that you have to use stubby to screw in.

There is also another test I would probably do - cylinder leak down. Tool is readily available in Harbor Freight for 30 bucks. (link below)


Other than that... maybe pull up wiring manual and check continuity and short to ground of wires going to #1 injector.
Thanks for the suggestions. Yes, it is sort of a PITA. In my mind I now refer to the CEL as the HBL (High Blood Pressure Light)

The local NAPA lets me borrow tools, and they happen to have a nice Leakdown Tester. In fact, I used it a few months back to determine head gasket issues after over-heating.
 

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1998 T100 SR5 2WD
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13,575 Posts
Since we've isolated the issue to be with only cylinder #1 and not the injector, coil, or spark plug, it's gonna come down to wiring. The injector should be gitting 12VDC at all times when the ignition key is on. It's the ground that's switched/pulsed from the ECU that fires the injector. ;)

The wire fer injector #1 is white/red stripe. It should be a straight connection from the injector connector to the ECU. According to my 1998 EWD, it looks like that wire is on the ECU connector D, pin 10. You'll have to do a continuity and resistance test from there to the injector connector to make sure there aren't any issues with the wire. The other suspect would be the power splice connector E3 but there are many other items running off of that connector that would be affected if that was the issue. Still wouldn't hurt to inspect it from there to the injector connector. You can also inspect the wiring harness connector just to make sure the wire isn't just hanging on by a thread or the insulation. ;)
 

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1997 T100 RWD Auto
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72 Posts
Discussion Starter #5
Since we've isolated the issue to be with only cylinder #1 and not the injector, coil, or spark plug, it's gonna come down to wiring. The injector should be gitting 12VDC at all times when the ignition key is on. It's the ground that's switched/pulsed from the ECU that fires the injector. ;)

The wire fer injector #1 is white/red stripe. It should be a straight connection from the injector connector to the ECU. According to my 1998 EWD, it looks like that wire is on the ECU connector D, pin 10. You'll have to do a continuity and resistance test from there to the injector connector to make sure there aren't any issues with the wire. The other suspect would be the power splice connector E3 but there are many other items running off of that connector that would be affected if that was the issue. Still wouldn't hurt to inspect it from there to the injector connector. You can also inspect the wiring harness connector just to make sure the wire isn't just hanging on by a thread or the insulation. ;)
Thanks Bam! That is good info to explore. Luckily I own a fairly decent volt/ohm meter with an audible continuity tester. I will check wiring and also do the leakdown test like CreoX suggested.
 

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1998 T100 SR5 2WD
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13,575 Posts
Another thing to check is that the connector hasn't been compromised. Is the socket contacts the same distance apart or does it look like one or both are bent and loose? ;)
 

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1997 T100 RWD Auto
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72 Posts
Discussion Starter #7
It is possible that I have found the issue.

I was googling around and found some guys on youtube who were chasing down an identical issue as mine: random misfire on cylinder 1 after 20 miles or so. They were blasting the problem with what some people call the "New Parts Canon", replacing everything they could think of with new parts, starting with plugs, wires, injectors, MAF Sensor, both o2 sensors...etc.
Finally they identified some play in the crankshaft, and figured out the play was causing random misses on the crank-shaft sensor.

I checked my crankshaft, and do not have play; however, I took out my crankshaft position sensor to clean the connections and found it was covered in mud and debris. On top of that, the plastic part that bolts the sensor to the engine was cracked and fell to pieces when I pulled it out:

283140



When I was doing the timing belt this summer, I failed to pull that sensor out and inspect it. Also I sprayed out the area to clean it up before putting the new timing belt in. I must have blasted all that debris onto the sensor.

I am ordering a new sensor. Meanwhile, I am cleaning this one up and seeing if I can epoxy the bolt hole back together so I can test if it fixes the issue, but it looks like a likely culprit.


Stay tuned.....
 

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1997 T100 RWD Auto
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72 Posts
Discussion Starter #8
Well, still having the same issue after replacing the Crank Sensor. However, the crank sensor really did need to be replaced, so I am glad I ran across it now and not after it falling out on the road somewhere.

I think my next move will be to tear down to the timing belt and have a look at things to see if anything is out of whack.

@CreoX I think you mentioned you had discovered a timing belt issue some time ago. Can you point me to where that thread is?
 

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1998 T100 SR5 2WD
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13,575 Posts
I would check the wiring first before you start tearing things apart especially that fuel injector wiring harness. ;)
 

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1997 T100 RWD Auto
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72 Posts
Discussion Starter #10
I was planning on just taking the covers off so I can inspect the timing belt and such. I think I can do that without removing the crankshaft or the timing belt.
But you are right, wiring would be great to remove from the list of suspects.
 

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1997 T100 RWD Auto
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72 Posts
Discussion Starter #11
I am still chasing down this misfire. So far I have done the following (with no change):
  • Replaced Camshaft and Crankshaft Postion Sensors (both needed to be replaced)
  • Checked timing belt and timing marks (looks good)
  • Jumped the wires to cylinder 1 fuel injector back to the firewall, with a new pigtail on the wires
  • Replaced spark plug wires (needed to be replaced)
  • Replaced faulty Evap VSV wich was stuck open
  • Swapped out coils, spark plugs and fuel injectors with cylinder 5 (did this previously with cylinder 3)
The truck runs fine and is getting 20 ~ 21 mpg. My fluid levels are not changing at all. I did a compression check and it looks fine.

Any ideas on where to look next? I have been trying to avoid using the new parts canon. So far I have only replaced parts that clearly needed it.

In my county we do not have to have smog inspections except at time of purchase, so I am not under any pressure to solve this.

I do not have a live OBD2 Reader, so I am thinking I should invest in that next so I can try and figure out if there is a particular event that triggers the misfire. I was looking at the UltraGauge Blue, but might have to settle for something slightly cheaper from Amazon. Does anyone have a favorite model for a Bluetooth OBD2 Reader?
 

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1995 T100 2WD
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1,761 Posts
I guess I should introduce the same misfire, I could use 20-21 mpg:)
I think BZP is or has experience with the Ultra-Guage scanner.
But I'm pretty sure he has more than one:)
 

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1997 T100 RWD Auto
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72 Posts
Discussion Starter #13
I guess I should introduce the same misfire, I could use 20-21 mpg:)
I think BZP is or has experience with the Ultra-Guage scanner.
But I'm pretty sure he has more than one:)
Are you saying that you have the same misfire? or are you saying you should try to get that misfire so you can get better mpg?

I am driving a 2wd automatic. I imagine it gets better mileage than a 4wd
 

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1995 T100 2WD
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1,761 Posts
I haven't taken it on any trip in a long time so it spends it's life as my daily driver mainly around town.
Avg 16-17 mpg. I run 89 octane (Chevron).
Years ago I used too make long road trips regularly and I did get 20-21 when using my cruise control.
Mine has just over 200k on it.
3.4, 5 speed. I'm the original owner and only driver it's ever had.
 

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1998 T100 SR5 2WD
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13,575 Posts
The Ultragauge I have is the stand alone display version. I don't have any experience with the UG Blue with the app. I do use my stand alone UG to provide basic numbers on from my OBDII sensors like fuel trims, O2 readings, hard and pending codes with reset capabilities, MAF readings, coolant and intake air temps, and gas mileage. ;)

I just returned from a trip to Kansas and the best I got was almost 31 (30.7) mpg at 65 mph hand calculated (actual miles traveled/actual gallons filled). Most of the highway miles I have are near 26 mpg or better. Best I ever got was almost 35 mpg (34.91) at 65 mph but with the AC off. ;)
 

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1997 T100 RWD Auto
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72 Posts
Discussion Starter #18
The Ultragauge I have is the stand alone display version. I don't have any experience with the UG Blue with the app. I do use my stand alone UG to provide basic numbers on from my OBDII sensors like fuel trims, O2 readings, hard and pending codes with reset capabilities, MAF readings, coolant and intake air temps, and gas mileage. ;)

I just returned from a trip to Kansas and the best I got was almost 31 (30.7) mpg at 65 mph hand calculated (actual miles traveled/actual gallons filled). Most of the highway miles I have are near 26 mpg or better. Best I ever got was almost 35 mpg (34.91) at 65 mph but with the AC off. ;)
Wow. This is probably a whole other thread, but it would be great to read about how you got there.

I did notice an uptick in my gas mileage after doing head-gaskets, timing belt, water pump and hunting down vacuum leaks.
 

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1995 T100 2WD
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1,761 Posts
Wow. This is probably a whole other thread, but it would be great to read about how you got there.

I did notice an uptick in my gas mileage after doing head-gaskets, timing belt, water pump and hunting down vacuum leaks.
Lets just say BZP's T100 doesn't look like ours anymore :)
 
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