Hi Guys!
My STR ECM is hunting, or surging, with a 2-5 hundred range of surge. Sometimes it does it, sometimes it doesn’t. But often enough that I suspected a vacuum leak.

So I tried propane and got no change in RPM anywhere.

Next I broke out the Hookah, got some good smoke (and a little buzz lol), found a tube, disconnected here and started blowing smoke.


Hose used to connect to vacuum system.

When I apply smoke, I see some smoke coming from this area:



Looking from passenger side, down into area of throttle body. Larger vacuum line moved after checking it. Trouble light cage seen in the top of the image, used to light the area. Corner of passenger side intercooler shown in the bottom half of the image.

Using an inspection camera, I can see the connection of the two vacuum lines to the throttle body and the smoke isn’t coming from there.
the smoke seems to be coming from deeper and more forward of this area.



Yellow arrow shows the two line connections I can see, no smoke. Blue arrow shows the area I can see smoke, but cannot seem to see the origin os said smoke.

The vacuum routing diagram sticker seems basic, so I was wondering if there was a better vacuum line diagram out there to help me find the leak?

Smoke only seems to be coming from the passenger side area, none is seen coming from the other side of the same area.

Thoughts?

 

Are you chasing a particular issue? Like a P0171/174 code?

Several issues over the years with the design of the vacuum hose between the brake booster and the throttle body.

 

I don’t have any codes, just the hunting/surging and the smoke with a source I can’t seem to see.
The smoke seems to be coming from the passenger side, while the booster is on the drivers side.
That being said, I’m not 100% sure where the booster vacuum line connects to the throttle body.

 

The yellow arrow is pointing strait at the problem prone brake booster pipe push connector.
any vacuum leak needs remedying.
spraying butane or any flammable gas will not alter the rpm. As the ECM fixes the rpm instantly.
If you have a look at your short and long-term fuel trims via OBD it will tell you if there is an airleak.
and how bad it is with percentage. and if you do the same test with butane while watching the fuel trims -
you will see the numbers change as the ECM alters the mixture due to your gas insertion. That’s how fast it fixes rich lean conditions .
but truthfully what you are explaining could well be the common TSB torque converter/transmission serge.
its well documented here .
does it only do it when cold ?

 

+1

First, check LTFTs, which should be close to zero - see threads on what to do for air leaks.

Second, especially if the LTFTs are out, watch STFTs as it hunts. Then if they're swinging around try spraying propane or the like sparingly and near each possible leak point. If you hit where there's even a tiny leak the STFTs respond instantly.

 

Thanks for the info, I agree it is accurate.

However I can’t help but think that the smoke test (combined with the surging/hunting) clearly indicates a leak.

The surging was not present when I bought the car, it has slowly come on over time and the engine temp seems to make little difference (cold or warmed up).

So it seems reasonable to conclude there is a vacuum leak, and the smoke shows me the area of the leak. But after spending some time with both a bright light and an inspection camera... I can not pinpoint the source. However I can’t see everything either because of all the stuff packed in this area.

This is why I asked about a better, more comprehensive vacuum line diagram for the 2003 STR with the SC 4.2L engine.

So again, I appreciate the info about LTFT, STFT etc. Sincerely I do.

But what I really need is a better vacuum diagram to help me track down the leak. Any one know of one they can link me to?

I thank you for your time

 

Humm..

As Andy pointed out a few posts back. The known vacuum leak issue is where your yellow arrow is in the photo. I know mine is an issue and I'll be fixing that over the winter. The press fit hose has an O ring that appears to bake over time and the hose loses any kind of seal to the throttle body. Since you have access to a smoke machine..try the same test and wiggle the hard plastic hose that runs from the booster to the TB and see if the quantity of smoke changes.

You mentioned the surging is in the 2-5 hundred range. Is this at idle or cruising? I'm thinking if it's at cruising speed that would represent a fairly substantial change in vehicle speed?

 

I should probably clarify:

The surging/hunting usually occurs when the engine RPM is between 1k-2.5k.

The surge range spans an average of 500 RPM. So, for example, the RPM needle will bounce between 1.5k-2k as I enter the highway and accelerate to cruising speed between 65-75mph.

Then it often seems to work itself out and the surging goes away. But sometimes it returns while cruising, more often when I give the engine some gas to accelerate.

Watching from another car you probably couldn’t tell anything is happening. But riding in the car it feels like I am slightly pumping the gas as I accelerate.

Speed itself doesn’t seem to matter, as it will do this accelerating up to 40mph on thoroughfares, and to 75mph on the highway.

I will check the seal on the booster line, and check everything again with some wiggling.

There is a seal between the supercharger and the elbow, and the bottom portion of this seal is one thing in the area that I can’t see. I’m hoping the smoke isn’t coming from there. I also know there is a line that runs under the super charger. I can’t remember if it’s a vacuum line or a coolant line, hoping it’s not that line.

Basically, I really hope it’s the Booster-to-TB line.

Would still really love a more comprehensive vacuum system schematic...

Would also love to have this become a resolved thread



Fingers crossed, will advise.

 

Sounds like TSB S307-14
but that would be as well as or perhaps instead of an air leak.

 

I had 0171 and 0172 codes and that $5 push connector was exactly what was leaking. The heat destroys the check valve in it after time. Took mine to O'Reily's Auto Parts and matched it with the photos on scree. Worked great...no more codes. You are right about the smoke test.

 

So this surging is both cold and fully warmed up?

Try using manual mode to shift through the ranges as you drive for the next couple of days and see if it changes the behavior?

I'm not doubting your vacuum leak diagnosis and I hope it's not the gasket you refer to. I'm hoping that since you have access to a smoke machine you do have access also to a scanner. If we are indeed dealing with a vacuum leak the fuel trims will show it as JagV8 suggested. Short fuel trim and Long fuel trim are a constantly changing number and different manufacturers set a threshold to determine how far they can be apart from each other and for how long. IIRC Most of the vehicles I dealt with in the era of our cars didn't like to see more than 9% difference for more than a few seconds at cruise. It is feasibly possible that a P0171 or P0174 could be in "pending" status as the PCM hasn't seen seen enough difference in the correlation of these two pid's to flag the check engine light. Let's look at your fuel trims and post back here.

 

Initially I would like to answer the questions. It does seem to surge/hilt less once engine/environment temps are warmer. But it doesn’t go away.

JagV8 is right, as are all of you.I work in Emergency medicine and the garage is too far away to be there and be on call. As I am on call this weekend all I can do for now is sit in the hospital parking lot and check things at warm idle. I will recruit a friend to watch the trims while I cruise around. I will propane suspect positions while observing the STFT once I can get back in the garage. Will update with that new info.

For now I can give you info seen on the iCarsoft in the parking lot at idle.

 

I got off work. It was hovering just above freezing, so I started the car and let her idle for about 20min to get a bit warmed up. Not hot, but warmed up a bit.



I hooked up the iCarsoft and pulled in the data stream for short term fuel trim and long term fuel trim, banks 1 and 2. Also pulled over the fuel rail pressure, intake manifold absolute pressure, MAF flow and a couple other fuel trims that ended up being useless.



I sat there snapping pics over the course several min, watching the STFT grow, then correct, grow, then correct as shown. Idle is a bit rough.



Starts as shown above...

STFT grows...

Grows...

Grows...

Then corrects...

Then starts growing again. Repeat.

I also had a print out of what the fuel rail pressure and intake vacuum should be, from the jagrepair +3000 page repair manual I found online. (Link at end of post)



Fuel rail pressure for my ‘03 STR should be 300kPh (500kPh at WOT) Intake vacuum should be 51-75 kPh.

Then I drove literally a few miles home (not where my auto workshop is unfortunately).

Checked iCarsoft again:








She did some surging most of the way home, and I never got above 40mph as this was all city streets between the hospital and my home.

Just providing the data I have thus far.
Link to the repair manual:

http://www.jagrepair.com/images/Auto...M-Workshop.pdf

 

Oddly, I work on 55psi being OK fuel pressure, which looks to be about 380kPa.

I don't see anything odd about those trims...

 

As jagv8 states . Your fuel trims are within tolerance.
And the fuel pressure is bang on too .
if you have a leak it’s a very small leak .
though I noticed your MAF is slightly high . It should be 4 to 6 gps .
6+- indicates a slightly dirty MAF sensor .
and it throws your trims off a little.

BTW the vacuum line pic you show does show all the vacuum lines in the STR .
there are only 3 . 1 for brake booster . 1 for supercharger bypass diaphragm . And 1 for the Fuel pressure regulator.

Plus the two bigger plastic ones one for the charcoal canister .
and one for the PCV .

i suggest you do a vacuum test on your boost diaphragm as that could explain both your symptom and where your smoke test was escaping.
there is also a short rubber bypass connector hose to check in the vicinity,
between the intake elbow connecting the supercharger to the charge hat .

 

Maybe we have an EGR valve duty cycle issue?

 

[QUOTE=Catfan01;2169777]Maybe we have an EGR valve duty cycle issue?

EGR . is not used or cycled till above 2500rpm
and you will see a p0420 if it fails a cycle test , or fails to open or close .
i doubt it will be that .

i'm still thinking it’s the widely documented transmission surge ,
not to be confused with the transmission lurch.
mine does it , it’s worse in winter . And although the engine might be up to temperature
the surge will not disappear until the trans is up to temp . 15mis later

 

With no codes and trims looking ok I feel I can assume that any vacuum leak smoke is showing is barely there and not my first priority. I’m not saying I won’t still work on finding the source of the smoke etc. But it seems this leak could be an incidental finding and not the source of the surging. If I find a leak I will update here to keep the thread relevant and helpful to others.

Meanwhile I will shift my priority to a transmission service (Solenoid, seal adapter, tube gaskets, that gasket between the computer and the solenoids in the valve body, pan gasket, pan and o-ring) and then get the aforementioned transmission software update from the dealer.
Once that is done I will update.

I do have questions about proper solenoids and where to get the new computer/solenoid gasket in the valve body. But I don’t want to tangent this thread away from its original topic too much.
I will start another thread if I can’t find the answers by looking at existing threads.
But until then, thank you once again for the help and info. This forum is awesome, as are all of you.

 

i think following up on a started thread is priceless .
but i'm not not telling you to go re-build your trans -, though you can try what you like .
and i can only recommend a trans oil and pan filter as a minimum and wise thing to do regardless .
but in fact this TSB it's widely known to be a torque converter orientated repair . so going through valves and seals my be in the wrong direction .
and that would only be if my assumption is correct .
you really should trouble shoot this further .
and if it turns out to be the surge you can in-fact put up with the harmless surge .
and maybe knock the j-gate shifter down one cog to see if this helps . for free.
because it mikes mine absolutely bearable . and operates perfectly after a short bit of patience .

 

Well, no one said rebuild the transmission. Or rebuild the valve body for that matter.
It seems, judging by this and a response on another thread specifically about the valve body service, that clarification is needed between a transmission rebuild and servicing the mechatronic valve body.

One is pretty easy if you are replacing the pan, the other is an epic transmission removal and rebuild job requiring lots of special tools and expertise I don’t have.

Now I admit that I miss things sometimes. But searching this site finds no apparent threads/how to’s regarding servicing the mechatronic valve body for the 6hp26 transmission in my 2003 STR. So perhaps I should go ahead and make a how to video and write up the process.

Currently the only videos on YouTube for the 6hp26 are for units installed in BMWs. So as soon as I verify transferable parts I am totally doing this.

So as to not hijack this thread, here the link to another thread I started about this valve body service:

https://www.jaguarforums.com/forum/s...0/#post2170206