3.8l VT hesitation / misfire under light load when warm

[Reuben Campbell]

Ok, so next update.
have got the wire sorted out. Its all happy again now.

Just push it in via the back when the plug is on. You can check the depth of the other pins so you know roughly how far it needs to go in - Thanks Ephect - thats basically what I did in the end. I also attached the plug to the dfi plate first where I can see it easy, then bolted the dfi and coils down last.

back to starting normally.
But now back to where i started over 2 weeks ago.

Speaking with a mechanic friend (in between his jobs at work) he has been looking at the o2 sensor readings and long term fuel trims.
o2 sensors are reading high voltage at about 800mv constantly - ie reporting a rich condition.
the long term fuel trim is sitting on the negatives (~ -15%) at idle and at 2500rpm -so rich conditions again.
both these explain the smell of fuel from the exhaust - its just blowing out the back.

Have also tightened up the fuel purge line from the TB to the purge line valve thingy behind the drivers side head to ensure no air leaks there (hose clamps on it) as it was a bit loose. - nil change

also clamped off the purge line just before the valve thingie in the engine bay, incase excess fuel was getting back to the motor via the charcoal canister purge line when it shouldn't. - nil change

 

[Lex]

Ok, so next update.
have got the wire sorted out. Its all happy again now.

back to starting normally.
But now back to where i started over 2 weeks ago.

Speaking with a mechanic friend (in between his jobs at work) he has been looking at the o2 sensor readings and long term fuel trims.
o2 sensors are reading high voltage at about 800mv constantly - ie reporting a rich condition.
the long term fuel trim is sitting on the negatives (~ -15%) at idle and at 2500rpm -so rich conditions again.
both these explain the smell of fuel from the exhaust - its just blowing out the back.

Have also tightened up the fuel purge line from the TB to the purge line valve thingy behind the drivers side head to ensure no air leaks there (hose clamps on it) as it was a bit loose. - nil change

also clamped off the purge line just before the valve thingie in the engine bay, incase excess fuel was getting back to the motor via the charcoal canister purge line when it shouldn't. - nil change

Whats the fpr (fuel pressure regulator) like?

 

[Reuben Campbell]

Whats the fpr (fuel pressure regulator) like?

I checked this early on in the piece.

I just checked it again, and decided that ill replace the hose as it was looking a bit shabby.

But no signs of fuel leaking back into the vacuum hose and into the intake manifold.

Also just sprayed brake cleaner around the seal joins again, looking for a vacuum leak.

My mechanic friend is convinced that its a vacuum leak somewhere.

As a summary of stuff done thus far

Replaced
Idle Air Control solenoid - new
Throttle Position Sensor - new
Mass Air Flow sensor - second hand
Crank position sensor - new
Cam Angle Sensor - New
Ignition leads - new
Intake manifold gaskets - new
Front crank seal - new (while the pulley was off - not related)
Coils - new
DFI plate - new
Spark Plugs - new
Air filter - new
Fuel Filter - new
oil filter and oil - new
PCV valve in intake - new
injectors - serviced with o-rings, filters and pintle caps. Ran brake cleaner through them with a injector pulse tool and sprays look ok.
belt tensioner - new (everything was apart so it made sense as I was avoiding it before - not related)
fuel regulator to plenum hose (old one was perished)

EGR valve - scrubbed out and appears to be moving correctly
intake manifold to throttle body hose (old one fell apart when removing it)
hose clamped purge line from purge sensor to Throttle body

clamped shut and checked connections for leaks - visual and with brake cleaner.
vacuum hose to brake booster
vacuum hose to purge line/charcoal canister

No error codes using Advanced Engine Diagnostics.
No dash lights on
No signs of fuel in fuel pressure regulator vacuum line
sprayed brake cleaner over all joins trying to find the leak - nothing yet.

Fresh fuel in tank (90% full)

02 sensors reporting rich fuel conditions
long term fuel trim reporting rich fuel conditions

Current symptoms
rough idle, which drops by 100-200 revs every couple of minutes and picks itself up again to normal idle
when accelerate anything above the lightest touch, the car shudders and produces no power.
when parked, you can bring the engine revs up to redline and it doesn't shudder, as long as you do it very gently.
strong fuel smell (reported by others) from the exhaust. - I have a terrible sense of smell

 

[Lex]

strong fuel smell (reported by others) from the exhaust. - I have a terrible sense of smell

Pull the plugs one at a time & inspect it, etc until all are checked.
I'd be checking the leads too?
Shuddering usually points to leads & spark plugs.

Try & determine which cylinder(s) are mis firing by taking one lead of at a time while engine is running.

This may even be mechanical as in valves & or springs? Had the rocker covers of?

Then there is all the parts you have thrown at it?
New parts are questionable these days.

Do you have all the old parts?

What condition are the injectors?
Are they leaking fuel into the sump? Pull the dip stick & have a smell.

If the injectors have been replaced, are the correct ones?
Vs injectors are not the same as vt injectors.

 

[Reuben Campbell]

Pull the plugs one at a time & inspect it, etc until all are checked.
I'd be checking the leads too?
Shuddering usually points to leads & spark plugs.

Try & determine which cylinder(s) are mis firing by taking one lead of at a time while engine is running.

This may even be mechanical as in valves & or springs? Had the rocker covers of?

Then there is all the parts you have thrown at it?
New parts are questionable these days.

Do you have all the old parts?

What condition are the injectors?
Are they leaking fuel into the sump? Pull the dip stick & have a smell.

If the injectors have been replaced, are the correct ones?
Vs injectors are not the same as vt injectors.

Thanks Lex for the tips - really appreciate the effort.
Ive got to head off to the fire shed for our friday night meet, so no more work for now.

The plugs and leads are all new (last 500km) - but will inspect them either later tonight or tomorrow morning for sludging or blackness

Ill also redo- the 'pull-a-plug-lead' test. When I did it initially every plug removed made it worse - ie all the cylinders have a working plug.
Its hard, cause it only shudders/misfires when revving the throttle suddenly.

The new parts - yep, i still have all the old parts. i could fit them back.

Injectors - I have serviced these with new o-rings, pintle caps and filters. Visually, they all seen to spray evenly. (ill update my list above)
No they haven't been replaced in my time.

Rocker covers - I haven't pulled them yet. This needs to be the next check. Ill aim to have this done tomorrow.

Ill update again tomorrow morning with the pull a plug test, plug condition and under the rockers.

 

[ephect]

Had a quick skim once the thread. I saw you planning on replacing O2 sensors. Did this happen?

Of not that's your next thing from a reputable auto store so you can take them back. Not ebay

 

[Reuben Campbell]

Had a quick skim once the thread. I saw you planning on replacing O2 sensors. Did this happen?

Of not that's your next thing from a reputable auto store so you can take them back. Not ebay

Nope not yet - I havent got to an auto shop to order them yet.
Ive got some 2nd hand ones from a wreck i can pull and use.

 

[Reuben Campbell]

So, Ive had to give up on this myself and have dropped it off to a local mechanic to see what he can find.

If he comes back with an answer, ill update here to let people know

 

[Reuben Campbell]

Well. The mechanic has rung me back with good news

the car is running fine and all fixed and running fine.

he says that No3 and No5 plug leads were not 100% clipped on causing them to short the plugs out intermittently when the engine moves during acceleration!
No 5 lead was a bit tight when I've installed it so was pulling at slight angle, enough to short when the engine moves.
No 3 lead , the spring was not sitting right, causing it to short intermittently as well.

That doesn't answer what the original problem was, but its since the new leads (the first thing I changed) were now contributing to the problem, once I replaced the offending sensor, It wouldn't have been any better.

Its also possible, that it was just old shi**y leads initially, and due to poor fitment on my behalf, I couldn't see the effect of the fix - this is plausible as there seemed to be an improvement in the issue after I did the leads several weeks ago, but its intreating to note that I have pulled and replaced those leads at least twice since the initial changeout and pulled them on/off trying to hunt down the fault several times.
I would have thought that i would have at least accidently made those plugs better at some point as I have never had this issue in the past when replacing plugs, or swapping out leads.

Ah well, all's well and ends well- just annoying that it took this long.

I pick the car up next Wednesday, and will give it a test run.