Flashing CEL after Throttle Body Clean (1 Viewer)

[benjrblant]

--Edit--
Solved below in post #14
--Edit--

Hi,

I spent the weekend doing some PM on my 1997 LX450. It had a P0401 code when I started, was due for new plugs, and had a very leaky VC gasket. I found a torn vacuum line, a likely suspect of the 0401 code so I stopped after the throttle body and did not go further into the EGR system or the intake manifold. I went as far as this:

I installed a new VC gasket, spark tube gaskets, new Denso spark plugs, distributor cap and rotor, new throttle body gasket, and a new air filter. Most of the vacuum lines I could reach were replaced. The engine oil and filter were changed. All parts are OEM. Reassembled:

I'm now getting a flashing CEL with the following codes:
P0300- Random multiple misfire detected
P0301- Cylinder1 misfire
P0305- Cylinder5 misfire
P0306- Cylinder6 misfire

On the upside, the P0401 seems to be gone. Woo?

I've looked over the engine twice, there do not appear to be any forgotten vacuum lines or electrical connectors and I've double checked the plug wire numbering.
I'm happy to hear any pointers or advice you can share regarding this.

Thanks!

 

[UltraFJ40]

that's perplexing. Did you use OEM wires and seat them properly? I think these Chinese crap are not good for carrying the current needed. "Just get by seems to be the slogan here".

I might be wrong but that's my belief.

 

[benjrblant]

that's perplexing. Did you use OEM wires and seat them properly? I think these Chinese crap are not good for carrying the current needed. "Just get by seems to be the slogan here".

I might be wrong but that's my belief.

The wires are Denso but not from Toyota. They are not new to this install and had been working well previously.

 

[gnarlytoes]

Try swapping the old dist cap and rotor back in one at a time and then both.

 

[Proven]

Did you anger a ground wire?

 

[BILT4ME]

The fact that you cleaned the throttle body will throw some codes for a bit.

Clear all your codes (if you don;t already own one....get a UltraGauge so you can read/clear codes on the fly.

Cleaning the TB will throw off the firing properly and throw codes on the O2 sensors for a bit. Run it for about 50 miles and that should clear everything out. Clear the codes before and after.

 

[benjrblant]

Try swapping the old dist cap and rotor back in one at a time and then both.

Good idea to isolate components that might be at fault.

Did you anger a ground wire?

I definitely angered something.
Pulling plug wires 1, 2, 3, 5, and 6 confirmed that these plugs are getting spark, and the dizzy cap only fits in one orientation so I couldn't have botched that!

The fact that you cleaned the throttle body will throw some codes for a bit.

Clear all your codes (if you don;t already own one....get a UltraGauge so you can read/clear codes on the fly.

Cleaning the TB will throw off the firing properly and throw codes on the O2 sensors for a bit. Run it for about 50 miles and that should clear everything out. Clear the codes before and after.

Codes were cleared with a scangauge and returned immediately. It seemed slightly smoother after idling for 10 minutes but that could've been me getting used to the rumbles.

I'll try running it for a bit, if it doesn't clear up I'll try the old dizzy cap then pull and inspect the spark plugs. Thanks for the help everyone!

 

[BILT4ME]

Good idea to isolate components that might be at fault.


I definitely angered something.
Pulling plug wires 1, 2, 3, 5, and 6 confirmed that these plugs are getting spark, and the dizzy cap only fits in one orientation so I couldn't have botched that!



Codes were cleared with a scangauge and returned immediately. It seemed slightly smoother after idling for 10 minutes but that could've been me getting used to the rumbles.

I'll try running it for a bit, if it doesn't clear up I'll try the old dizzy cap then pull and inspect the spark plugs. Thanks for the help everyone!

Is #4 not getting spark?

 

[benjrblant]

Is #4 not getting spark?

#4 is getting spark. All 6 are getting spark. I pulled #4 at the distributor to avoid removing the intake tube.

 

[gummycarbs]

What's the resistance from the front ground (on the bracket near the fuel regulator) to the battery? The ground wire is at a sharp angle, which could break strands, and the ground point doesn't look particularly clean.

 

[Tools R Us]

Not sure that it's your problem, but see some possibilities.

At location "A" the harness clip is broken, the harness needs to be held in place, if not is only supported by the pigtails/connectors. This clip failing is the #1 cause of harness dramas on the 1FZ motor. We check every one of them and if needed (very common), hold it with a couple of zip-ties, like this.

At location "B" some exposed wires are visible, over wrap missing. This is likely from the harness rubbing on the hot EGR pipe. If so, maybe a short? A short here can take out whatever wire(s) are randomly on that side of the harness, often injector(s). My first test would be to remove the clip remains, tie it back like above, confirm the harness is not touching the EGR pipe and see if the miss is reduced, if so, you know where the problem is. This can be done without taking anything apart,
takes some finesse, but doable.

At location "C" the injector pigtails are twisted around each other. Not likely a problem, but when it was apart, I would have unplugged one of them and routed it so they weren't twisted, have more slack. Low priority, but we have fought problems here, a real pain, so prefer to reduce the possibility.

At location "D" the harness clip is also broken/missing. If the harness isn't mounted, you are asking for problems. This one is a much less priority than the one marked "A" but while in there would have tied it to the mount.

 

[ZackR]

I'd put my money on an issue inside the fuel injector wiring harness where is passes the EGR. In @Tools R Us post this would be area B.

 

[inkpot]

Wiring failures in these 4 positions are The Most Common performance/ CEL problems that we encounter on 80s. Lots of 80s, including mine, more than once!

 

[benjrblant]

Solved: Plug Wires were incorrectly placed. Like an idiot and a total noob. After a day under the hood and a late(ish) evening, I guess I wasn't being as attentive as I should've been and missed this twice.

Thanks to everyone for their help and input, and to @Tools R Us for pointing out a number of potential problems waiting to happen. I'm ordering a heat shield for the wiring harness and securing it properly.

I've attached a section of the FSM for troubleshooting misfire codes that I found particularly helpful. Interestingly, the ECU detects a misfire by monitoring the speed from the camshaft position sensor and the crankshaft position sensor. If it detects a variation from normal in any 200 or 1000 revolutions, it will illuminate the CEL.

If it detects a significant number of misfires, the CEL will flash indicating that too much fuel is passing through the exhaust and there is a risk of overheating and destroying the cats. The takeaway here is that a vehicle with a flashing CEL and a noticeable misfire should NOT be driven lest you roast the cats.

 

[Proven]

Thank you for making a SOLVED post.

So many of these just stop and there is no closure.

Glad you got it figured out.

 

[benjrblant]

A big frustration is searching through the dozens of threads with similar issues only to find that it dies off with no recourse. I hope that this can help someone else in the future.

 

[Proven]

@benjrblant now tell me about that cool looking red light you are using.

 

[benjrblant]

@benjrblant now tell me about that cool looking red light you are using.

I think It's a Lil Larry that I won in a raffle. It's proven quite handy- magnetic base, pocket clip, and hi/lo/flashing red toggles.
LiL Larry

 

[woodsman 44]

Not sure that it's your problem, but see some possibilities.
View attachment 1684206
At location "A" the harness clip is broken, the harness needs to be held in place, if not is only supported by the pigtails/connectors. This clip failing is the #1 cause of harness dramas on the 1FZ motor. We check every one of them and if needed (very common), hold it with a couple of zip-ties, like this.
View attachment 1684209
At location "B" some exposed wires are visible, over wrap missing. This is likely from the harness rubbing on the hot EGR pipe. If so, maybe a short? A short here can take out whatever wire(s) are randomly on that side of the harness, often injector(s). My first test would be to remove the clip remains, tie it back like above, confirm the harness is not touching the EGR pipe and see if the miss is reduced, if so, you know where the problem is. This can be done without taking anything apart,
takes some finesse, but doable.

At location "C" the injector pigtails are twisted around each other. Not likely a problem, but when it was apart, I would have unplugged one of them and routed it so they weren't twisted, have more slack. Low priority, but we have fought problems here, a real pain, so prefer to reduce the possibility.

At location "D" the harness clip is also broken/missing. If the harness isn't mounted, you are asking for problems. This one is a much less priority than the one marked "A" but while in there would have tied it to the mount.
View attachment 1684211

Does anyone have the part number for the harness clip...its the red "A" in tools pic ?

 

[ZackR]

Does anyone have the part number for the harness clip...its the red "A" in tools pic ?

Does anyone have the part number for the harness clip...its the red "A" in tools pic ?

When I did mine I just used zip ties to secure the wiring harness. They seemed more reliable than the clip and easier to replace down the road.