Misfiring in #5 & #7

Chewy

New Member
After completing my engine swap (97 1UZ into a 98 4Runner), the motor started right up but was misfiring badly. It seemed to smooth out at higher RPM's but shakes violently under light load (around 1200-1500 RPM). I was finally able pull the codes and came up with this:

P0300 - Random/Multiple Cylinder Misfire Detected
P0305 - Misfire Detected, Cylinder 5
P0307 - Misfire Detected, Cylinder 7

My friend and I did a little troubleshooting but kept getting the same misfires in # 5 and #7. Here's what we did:

-Checked continuity & resistance to #5 & #7 plug wires. Both checked OK.

-Inspected both spark plugs. Looked normal, but when compared to a known good cylinder (#3), they looked much cleaner.

-Swapped plugs with #3 and #5 to verify issue was not with faulty a plug. Checked good...no misfire in #3.

-Connected a test light to the #5 plug wire and started the car. It indicated good spark.

-Did a similar test with the #7 side, but put in a spark plug in place of the light. It also was visibly sparking correctly.

-Checked & cleaned injector electrical connectors.

I wish it were a simple matter of changing out some old components. But while I had this motor on a stand, I changed the caps, rotors, plugs, wires, etc. Everything was replaced with new. The plugs are Denso Iridium and can't exactly be gapped, but they looked the same when compared to a known good plug. Also, when I did the timing belt & tensioner, I triple checked to make sure I had it aligned properly. Plus, I think if it were off, there would be a few more misfires or problems?

After doing all this, we were pretty certain the ignition side of things was ok - the distributors were supplying power to the spark plugs. Not to mention, if something was up with a coil, distributor, or ignitor, it would manifest itself on #1/7/6/4 or #2/8/3/5, not 5 and 7...right?

We looked into the cylinder and saw it was a little wet. Not an obvious head gasket leak, but more like unburnt fuel. Both suspect plugs looked like they were working, and the presence of unburnt fuel made me believe the injectors were working as well. I had all the injectors cleaned and flow tested a while ago but hit them with a squirt of carb cleaner before installation to clean off the preservation oil.

I still need to do a compression check and maybe inspect the caps & rotors again, but have I missed something incredibly obvious? Anyone got any pointers?
 

Zuffen

Super Moderator
Staff member
Have you checked the cold start injector?

If the injector is leaking it can allow fuel to drain into a couple of cylinders.

Sounds a little like your problem.

This was the fault with a simillar problem which was solved in the last few days.
 

Chewy

New Member
Wasn't the cold start injector discontinued in '93+ 1UZ's? My motor is from a '97 SC400 and I don't think I remember seeing one...
 

Chewy

New Member
Did some more troubleshooting today and the motor is still consistently missing. I decided to concentrate on one cylinder at a time and chose #5 since it's a little easier to get to...

I did a compression check and it was strong at about 190. Next I checked the resistance on the crankshaft position sensor and the fuel injectors. Both were perfectly within limits. Finally, I checked the voltage of the injector wires at the ECU; spot on at 12V.

So now what? I'm beginning to think it may either be a fuel pressure problem or a timing problem. I'm installing a Walbro 190 this weekend so I'll see if that does anything. But I still have my doubts about the fuel pressure beign the cause. Actually, I'm beginning to wonder if I installed the timing belt correctly. When I replaced the belt & tensioner, I followed a few of the different write-ups on this site. On the timing belt drive pulley, I aligned the pulley notch with the dot on the oil housing. Then I aligned the two notches on the cam pulleys with the raised marks on the back plates. According to the directions, this was correct. But I remember when I went to align the belt's "crank" line with the bottom of the crankshaft pulley, the "cam" lines didn't match up with their marks on the cam pulleys. I thought it was strange, but was under the impression as long as the pulleys were aligned correctly, the belt could theoretically be put on any which way. Is this right? Also, if the cam pulleys were off by a tooth or two, would it cause two dead cylinders right next to each other?
 

KTAStrophy

New Member
Hi there,
I know this is a pretty old thread, but did you ever get to the bottom of this, I have exactly the same problem with my 95 LS400 1UZ. Initially thought it to be an ignition issue so due to being old I changed the the rotor arms, leads and plugs. Spark is lovely, compression is fine, I dont believe fuel to be an issue. I'm tackling timing belt and water pump this week. Just struggling to understand why 5 and 7 arent playing ball?!
 

gloverman

Well-Known Member
On early engines 5 and 7 are on same injector drive, and have a shared power supply join in the loom. Also check leads are reversed on the dizzy cap, Ive seen this heaps.
 

KTAStrophy

New Member
On early engines 5 and 7 are on same injector drive, and have a shared power supply join in the loom. Also check leads are reversed on the dizzy cap, Ive seen this heaps.
Thanks for the quick reply! I bought the workshop manual on ebay (email to you joby) and cant find a wiring diagram anywhere! Not to worry at the moment though as it appears I've found a squirrel has made a nest in underneath the intake manifold in the V of the engine, and I can just about make out both knock sensors have been snacked on! I wonder what else has tickled his fancy anyways I'm going to strip it all back and do a proper clean up and test everything as it comes apart. If those wires have been chewed then I'm betting the injectors haven't been shown mercy, it makes sense why those two are dead if they share the same feed. Thanks again. I'll keep you posted.
 
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