Another diagnostic challenge (answer posted)

[Jeremy airjer W]

You'll love this one!

96 Toyota Camry, 2.2 liter, 280k miles

Customer complaint: Sever lack of power/hesitation and the check engine light is on

First things first I took this one for a test drive approximately 3 miles through city streets and back on the freeway. No issues.

I scanned for codes and found a P0302 (cylinder 2 misfire). I could see the misfire every once and a while on the scan tool but could never feel it.

My visual inspection revealed a plethora of new parts. Cap, rotor, wires, O2 sensors, and coolant temp sensor. HMMM!

Out of curiosity I swapped #2 and #3 plugs and wires. No change. I knew if I couldn't feel it the customer wouldn't feel it so I called the customer for more insight. The customer insisted that it would not accelerate, would sometimes stall, and there was no question that I would notice it. We decided it was best to test drive with the customer.

We drove for about 5 miles and sure enough it started acting up. It was backfiring, there was no power, the tach was bouncing up and down and we barely made it back.

My first thought is secondary ignition. I hooked up a spark tester in line from the coil to the coil wire and let it run. Spark was initially strong but would appear to degrade slightly (would turn from blue to orange). With the rapid firing from the coil it was hard to say if spark was ever missing. so I thought with the amount of miles on the original coil and the hot soak of the drive time it was a coil degrading. NOT!

New coil didn't effect it at all. So know what. This is where it gets interesting. The coil is controlled by the igniter which receives a signal from the PCM. With the lab scope connected to the input from the pcm, the out put to the pcm, and the control for the coil I let it run. I had a solid 5 volt square in and out and a good solid control of the coil. The only thing that was weird is when it acted up the control of the coil would not line up with the signal from the PCM. Also the time of the coil soak as well as the width of the signal to the PCM would get wider. AHA! The igniter is bad. NOT!

So I start over this time I check spark at a plug wire. Sure enough spark is intermittently missing so I know I'm on the right track with it being ignition related. At this point I'm stumped and call for a group meeting. It was suggested to check timing and to unplug the knock sensor (this engine also had a lower end/rod knock). No difference with the Knock sensor unplugged. We did find that timing was all over the place when the vehicle acted up.

I should note that when the vehicle acted up it was like a light switch. It ran great and then bang it would run bad. there was no in between.

The solution still has me stumped but after the repair the car ran great, never missed a beat, and has not been back.....yet!

So, What do you think?

[hunt fish repeat]

[PoorWordUsage] gremlins again, no question about it!

[Surface Tension]

You replaced the distributor? As to which part in the distributor went bad is still a mystery?

[Jeremy airjer W]

Not the distributor. The only thing in the distributor is a cam sensor. The vehicle will run with it unplugged. A 95 would have the crank, cam and coil in the distributor. The ingniter would still be external.

[thkime]

I had very similar symptoms on my 99 tacoma with a v6, finaly found a loose screw holding the pcm ground to intake manifold by the underhood diangnostic port, tightened that up and it ran great, until I threw a rod through the block a couple months later

[Scott K]

Was the windshield wiper loose?

[Surface Tension]

Was the windshield wiper loose?

Wow you took my 2nd guess, well that and a loose gas cap.

[efgh]

Did you check the muffler belt? Pluged cad.

[Surface Tension]

Being it had 280k on it, you probably told them a timing belt was long over due which justified a hunch so it wasn't just throwing new parts at it?

When the engine was cold the stretched belt constricted enough to keep the timing correct.

As the engine warmed the belt stretched and that created a miss.

Or I could be wrong and your going to tell me that engine went to a timing chain. LOL

[CAMAN]

Low blinker fluid?

[Jeremy airjer W]

Good gues Frank and although entirely possible not likely.

These belts will get so sloppy they will start to slap the trimming cover and never miss a beat. If the belt had jumped a tooth than there would be a running issue hot or cold.

CLUE:Since you brought it up the timming belt had recently been done at another shop and the problem started a couple months later

[PierBridge]

I'm going with a key-way installed incorrectly in crank shaft sprocket or warn groove in the crank shaft from not tightening balancer bolt or camshaft sprocket aliment pin missing or broken?

That's all I got and its probably going to be something stupid like you tightened the battery cables or switched the washer fluid to the purple stuff from the blue washer fluid....

[Jeremy airjer W]

your right it is something stupid!

I'll post the answer probably tomorrow.

[Macgyver55]

Did this involve an incorrectly done previous repair?

[PierBridge]

Did this involve an incorrectly done previous repair?

I'm assuming so... how about they left something under the valve covers, tool, socket? Oh wait you don't have to mess with the valve covers on a Yota when doing the T-belt.

[Jeremy airjer W]

Did this involve an incorrectly done previous repair?

getting warmer!

the timing belt was done correctly but there may have been an issue with the reassembly of the other pieces/parts........

[CAMAN]

Something with the alternator or serpentine belt not assembled properly?

[Jeremy airjer W]

Here is the answer...

Remember I said "I had a solid 5 volt square in and out and a good solid control of the coil. The only thing that was weird is when it acted up the control of the coil would not line up with the signal from the PCM. Also the time of the coil soak as well as the width of the signal to the PCM would get wider."

What I didn't mention was if the signal from the PCM was changing (the time in between getting wider). Truth is I don't know. Once I saw the signal from the PCM was good I automatically assumed everything in to the PCM was good and everything out was good. I decided I needed to find out if this was true.

While the vehicle was acting up I hooked up the lab scope to the signal wire from the crank sensor where it plugs into the harness under the alternator. While tapping into the wire the vehicle stalls, odd! I start the vehicle with the test lead in place and the signal was erratic to say the least. I grabbed the test lead to see if it had a good connection and the vehicle stalled. Aha! A pattern, now we are getting somewhere.

I start the vehicle again, this time with the test lead removed and wiggle and twist the connector. Nothing happens? I bumped the harness that goes to the alternator and bam the car dies.

That's when I finally figured it out.

When they did the timing belt, instead of removing the retainers that hold the crank sensor harness in position along the timing cover they cut the retainers and removed the harness from the cover. Upon re-installation instead of routing the harness along the passenger side of the alternator they wrapped it around the drivers side. This is where the exhaust manifold burnt the harness to a crisp. When the engine got hot it would intermittently ground the two wires, the engine would miss the wires would unground and back to normal until they grounded again. Again it only did this with the engine hot. Ran like a champ cold.

The customer had asked me on the test drive if I thought it could be the crank sensor. I was positive it was not. Either they work or they don't. I was right, however when I saw the wider signals I should have investigated further instead of jumping to conclusions.

[1johntimm]

Wow, good job tracking it down!

[dairyman]

Yep--------it always gives you a good feeling when a problems kicks you in the behind and then your able to get it fixed

[jmd1]

nice job, got to hate gremlins and the out of obvious issues. i had one on a fire truck one time. this truck was stationed in a bad part of town where the thieves would break in to the station both while the crew was there and not. so to give a bit more assurance, they put a car alarm on the truck. long story short, during the night the alarm would start going off on its own. they brought it to the shop where i started digging in and could not find the reason. after pulling nearly every wire from the harness looking for the short, i ended up in the back of the truck at the A/C compressor. this was a rear engine mounted truck. Disconnected A/C and the thing seemed to be fixed. Replaced compressor and found that the winding inside the clutch had shorted, the fact that the alarm folks tied into the ac wire allowed the alarm to sound if the clutch started grounding out. Just crazy and weeks literally of tracing wires.

[Macgyver55]

The first place I always look when diagnosing weird problems is anywhere a previous repair was recently made.

Too many times a guy will shortcut thinking "oh that doesnt matter" or its "no big deal" when in reality most of it does matter. Harnesses are run certain places for a reason, retainers are used for a reason and often we find it was something simple that someone thought didnt matter that caused a lot of headaches/expense afterwords.