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Discussion Starter #1
This is probably a good one for Enola or Gadget. I have a 96 3.4L motor that was completely rebuilt at 275K by an experienced Toyota Mechanic (side job). We installed headers to replace the stock manifolds and a cold-air intake was installed as well and about 5K ago plugs were replaced with E3 plugs.

Now at 299K I was driving to work and after the truck sitting for about 4 hrs, I went to start it up and it ran like ass. Rough idle, no power, etc. CEL on with intermittent flashing as I got it home.

CEL Codes: Random Misfire, misfire on cyls 2, 4 & 6

Plugs look ok, replaced crank pos sensor, cam pos sensor, new wires, CAT is ok (can see light through it & it was replaced back in '05).

Toyota buddy thinks leaky injectors or ECM. Could not find any vacuum leaks; removing cat does not improve symptoms. Once in high RPM things smooth out but still lacks power and runs rough. Fuel deliery seems to be fine but I'm at a loss.

I tore apart the intake plenum, removed and "DIY-flushed" the injectors with seafoam/gas mix; no evidence of leaks and spray pattern is now uniform for all injectors.

Any ideas? I haven't reassembled anything since cleaning the injectors.
 

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Mambeau / Admin
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No codes are being thrown other than misfire codes - right?

When - and how many times - has the timing belt been changed on this engine?

Once it started this misfiring behavior, it's been doing it continuously - right?
 

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Discussion Starter #3
You are correct, only misfire codes thrown. Random misfire and cyls 2,4&6. I'm essentially down one entire bank with contestant CEL that flashes intermittently at random intervals.

Timing belt has been done regularly and was last replaced at engine rebuild with Toyota oem parts (belt, tensioner and bearing).

Once it started these symptoms, they did not go away. I've been trying different things to get it fixed beginning with the potential obvious and inexpensive first. Once I clear codes, the truck throws the same codes within minutes.
 

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Mambeau / Admin
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There are all too many things that could cause a misfire condition.

Since this is an older Taco - what about the emissions / EGR stuff? Problems with the EGR system could cause a misfire.

Other culprits might include the MAF sensor and the engine coolant temp sensor. Have you checked them?

The fact that the misfires _seem_ to be concentrated on one bank makes me wonder if it could simply be a problem with your ignition wiring leading to that bank.
 

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Discussion Starter #5
I bought the truck used in San Diego back in 2000 from the dealership. When I moved back there in 07 and had to get it smog tested, it failed because it only had one Cat. When rebuilding it, I don't recall it having any EGR stuff on there and the headers replaced the stock manifolds. It's not throwing any emissions codes....never has before since I've owned it.

You bring up a good point on MAF (how does one determine if it's good or bad?)
 

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Discussion Starter #6
Also do you have a diagram of where the coolant temp sensor is located?
 

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Discussion Starter #7
Update: I pulled the plugs....passenger side (1,3,5) we're burned up pretty bad on the electrode end. The drivers bank (2,4,6) we're dark as night and carbon fouled to hell.

I put fresh plugs in (E-3 replaced under warranty) cleaned the MAF, swapped the injectors to opposite sides and put everything back together. Oh and the fuel filter was replaced.

The truck fired up and there's no change. It runs like ****, no power and barely idled before dying. I started it back up, drove 100 yes down the road parked in the driveway and it wanted to idle at 2,000 rpms. I went inside, came out and the truck will crank but won't think about firing. Any ideas? :selfbonk::brickknoc
 

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Mambeau / Admin
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Here (attached) is an illustration for the 1996 5VZ ECT location.
 

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Mambeau / Admin
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After the plug (etc.) changes, were the misfire codes still all localized in one bank? If so - was it the same bank as before?
 

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Discussion Starter #10
The truck didn't throw any codes....it was only running for about 3 minutes total. I pulled into the garage and I can't get it to start again. Btw thanks for the diagram of the ECT sensor.

If I can get it running, I'll wait for it to throw a new code and see if anything moved around.
 

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Not sure but could it be timing issue? TDC isn't really position correctly which caused misfiring in the first run?

Just thinking out loud.
 

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Mambeau / Admin
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Yep - it could very well be something out of synch with the timing components. However, there are too few clues available to pin it down to that ...

I'm hoping it's not the ECM.
 

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Yep - it could very well be something out of synch with the timing components. However, there are too few clues available to pin it down to that ...

I'm hoping it's not the ECM.
totally agree. It can be various issues at hand without narrowing down the basic
 

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Discussion Starter #15
Have not checked compression as the entire motor was rebuilt 20k ago. I'll pull out the injectors again along with the fuel rail and make sure there isn't anything in the rails that could clog the fuel delivery. I'll also have the injectors sent to Dr. Injector for cleaning and remanufacturing. While I'm in there, I'll look at timing too.

I do recall about a month prior that the truck overheated due to a failed radiator which has since been replaced. Could that have damaged the ECT Sensor? After the overheat, it ran fine the. One day, it crapped out and hasn't been the same since.
 

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Hey I dont know if you fixed the problem yet but I know from working at toyota that these foreign engines dont like aftermarket sparkplugs....sounds stupid but its true they run best on OEM plugs. Im not sure if you tried that yet but theyre cheap enough give it a try.
 

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Discussion Starter #18
Update:
I pulled everything apart. Fuel Rails are clear. New plugs and new ECM. Truck starts and runs but no change or improvement. I pulled the cat out and it just made the truck louder but it still ran like crap, no new codes have been thrown.

Going to drop off injectors tomorrow to be flow tested, cleaned and rebuilt/replaced. I'll also look for an ECT sensor to replace as well.

The last time I ran the truck (about a week ago) the cat was glowing but again, no codes or change in how the engine ran.
 

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Mambeau / Admin
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Have you checked the compression yet?
 

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Discussion Starter #20
So I think that I've got it fixed. I dropped my injectors off at Dr. Injector late yesterday afternoon and they were ready before noon today.

Two injectors were bad and bought re-manufactured injectors for $49.00 ea,, cleaning and new o-rings/seals was $24.99 ea. Results from flow testing: remaining 4 injectors were flowing 12-14% less fuel (105mL) with a ****ty stream that wasn't atomizing the fuel properly. After cleaning and matching the flow rate, all six were running at 120mL.


I also saw that the engine jumped timing, I'm guessing on the crank because the cam gears were both retarded by about 10-15°. Used an awesome trick that I read about so I didn't have to take out the tensioner, I just backed the bolts off about 3/8" which gave the belt enough slack to adjust the cam gears and reset the belt (same trick can be used for changing out a water pump if yours takes a ****).


I'm going to run some seafoam through it to get all the carbon build-up out of there. I started it tonight and it seemed to run pretty strong, throttle response is awesome. Taking it for a drive tomorrow.
 
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