Engine Hesitates when high load without shifting

I have a 2009 Cadillac CTS with 3.6 DI engine and 6 speed automatic transmission with 106K miles. Just recently I have noticed that usually around 50 mph if I give it partial throttle the engine starts to hesitate, sometimes badly. I can usually repeat this by putting the transmission in 5th and getting up to about 50 mph then stepping on the gas slightly while going up a hill. I have done some diagnostics but don't really know all the ins and outs of what I'm looking for. The car isn't throwing any codes. I have used bluedriver to get the data. Sorry if this is the wrong place to get help, but someone on the Cadillac forums told me this would be a good place to go. I have attached a few files, one with as much data as I could get. The hesitation was noticed during the last 20 seconds, for a period of about 5 seconds. The second file is something that bluedriver calls ModeSix (Not sure if that is standard terminology).

Hello,

I reviewed the log, It would have been nice to have the LTFT as well, but as far as I can tell looks like a dirty Mass Airflow Sensor.
based on what the O2's, RPM and STFT are doing.

If possible, clean the MAF, try and recreate the 10 minute drive test as close as possible and post another log file.

Thanks

Thanks! I already cleaned the MAF sensor. The car definitely ran smoother, but the hesitation still exists. I have a new one coming in that I plan on installing, but I'm pretty sure it won't resolve the issue as I had installed one for a quick ride and it still exhibited the hesitation. I will at LTFR pressure in my next test drive once the new MAF comes in. I can add all the data that bluedriver will record unless that's information overload.
Thanks!

That is info overload some trims were missing.

Ill post back which Data Parameters I want you to record.

The Bluedriver picks up data better with 6 or less PIDS, so we might need a two trip test lol

If anyone is watching this post, could you please post a fuel pressure spec for this GDI engine.

Thanks

I hope to see your MAF readings improve substantially.

Here's a graph of RPM Orange vs Fuel Pressure Blue where your hesitation occured, so I still wont rule out some type of fuel problem.

Interesting. Keep in mind to reproduce, which isn't completely necessary, but I know it'll usually happen, I do the following:
Get up near 50mph
Put the car in manual mode and force it into 5th gear
step on the gas about 20 to 30 %
Usually if I'm going up some sort of hill it'll start to hesitate.

When it's not in manual mode if the car fails to shift, as it loves to keep gears vs downshifting, it'll do the same thing. If I step on the gas any harder it'll downshift. I've noticed the minor hesitation in the past but recently it's gotten bad where the car jerks quite a bit when this happens. It almost always happens in the conditions I stated above though. In any other gear below 5 it seems to either shift or there's enough power to accelerate the car without hesitation.

Once you get me the data you want me to track and I get the new MAF sensor I'll do the additional runs. I really appreciate your help!

The Pids of interest will be

1. B1S1 voltage
2. B2S1 voltage
3. LTFT Bank 1&2
4. STFT Bank 1&2
5. Fuel Pressure in P.S.I............adjust your settings from metric to imperial for me please, tks
6. RPM
7. MAF

So, tests of importance will be, and BTW, feel free to send more than one log.

Warm operating engine.

1. hold at idle for minute, hold at 1500 rpm 1 minute, hold at 3500 rpm 1 minute

2. We need a wide open throttle test WOT, Best done in low gear for short burst, don't hurt anything. 5-10 secs should do. This one helps verify fuel delivery.

3. try and recreate your hesitation again, so it can be compared to the original test

Thanks

Paul

Weycraze wrote: That is info overload some trims were missing.

Ill post back which Data Parameters I want you to record.

The Bluedriver picks up data better with 6 or less PIDS, so we might need a two trip test lol

If anyone is watching this post, could you please post a fuel pressure spec for this GDI engine.

Thanks

I hope to see your MAF readings improve substantially.

Here's a graph of RPM Orange vs Fuel Pressure Blue where your hesitation occured, so I still wont rule out some type of fuel problem.

I can only find the low side spec: 55 to 60 psi koeo.

Looks like any information alluding toward diagnosing the high pressure side includes using fuel trim or the presence of a lean DTC.

Thanks Noah, I have that spec, so far I've only have STFT to look at until OP sends more data.

STFT slightly NEG then go POS at higher RPM/Load.

MAF seemed low to me 88g/s at around 3200.

B1S1 seemed a little sluggish as well, and the post O2's are just starting to switch infrequently, instead of holding steady.

When the OP gets more data, Ill boil them down in Excel for people to look at.

I'll try to get the measurements by Saturday. Also, what is B1S1? Is it possible that this hesitation is being caused by dirty fuel injectors? After getting the measurements I was going to try to add some BG44 to the tank. Thoughts?

Bank 1 Sensor 1(B1S1) Oxygen Sensor
Bank 2 Sensor 1(B2S1) Oxygen Sensor

These above 2 sensors the ECM uses for Fuel Control while in Closed Loop engine operation.

Bank 1 Sensor 2 (B1S2) Oxygen Sensor
Bank 2 Sensor 2 (B2S2) Oxygen Sensor

These above 2 are used to monitor Catalyst Efficiency.

Yes, it is possible Dirty injectors can cause performance/hesitation issues.

I like to use Seafoam in my fuel for everything!

We really need LTFT (Long Term Fuel Trim) data for both banks to go further.

Those 3 tests will provide the required info to proceed further.

So I got the part today and put it in. I suspect it's the wrong part because the car doesn't run nearly as well as it did with the old one so I'm returning it. I finally found the actual OEM part and have that ordered but it won't come in till the end of next week. I did run the tests that you asked while it was installed. Not sure this will help. Idle I did with the car in park. 1500 I couldn't maintain in park so I put it in manual and drove with it at 1500 rpm, same for 3500. I did the full throttle starting at partial as I had to get on the highway around a bend. The hesitation was easy to replicate, and it's at the end of the full throttle run recording.

I hate to be a pain, but the idle, 1500, 3500 need to be in park. just hold as best that you can! Idle and 3500 are the most important.

The WOT test sent the O2's rich so fuel delivery from the pump looks good.

Your Fuel trims are within 5%, which is very good. Except for the odd spike where Fuel pressure blips

Bank 1 LTFT at idle is -1.6, high RPM -2.3, so it's actually subtracting fuel, keep in mind these a very tight fuel trims that look pretty good.

Things that I don't like is the fuel pressure ups and downs.

If you're gonna install a new MAF. Post some more data and switch the Mass Airflow rate to Grams/ Second, keep the Fuel Pressure in PSI

Overall with the data I reviewed nothing blatantly stands out, other than what your fuel pressure was doing during the hesitation.

Let Me know which MAF you are using in the test data

Also, check your Mode 6 data on your bluedriver and look at the misfire monitors, are there any? if so post which cyclinders

I don't like what the Fuel Pressure is doing here on the WOT test after max rpm starts to drop

Paul

I'll get new data when the new MAF comes in. I'll be in Philly for work Wed/Thurs and I don't think the part is coming till Friday so I won't be able to post anything till next Saturday. Normally I'd say keeping 1500 in park shouldn't be an issue but the rpm would shoot up and then drop on it's own and if I tried getting it to go back up it'd shoot way above and then back down. It seemed really erratic.

Just some more stuff I see....

You RPM at idle is isnt very steady... MIN 531, MAX 660, +/- ~65 RPM

Fuel Pressure at idle same thing MIN 529, MAX 666

The Idle on this engine seems low to me.

MAF readings seem low too

Normally I'd say keeping 1500 in park shouldn't be an issue but the rpm would shoot up and then drop on it's own and if I tried getting it to go back up it'd shoot way above and then back down. It seemed really erratic.

This is the best info so far, I was wondering about this. If you've got erratic idle in park and no smoothness of rpm, it certainly wont be smooth in gear!

The list of possibles goes on for erratic idle, and most are beyond a Bluedriver's scope.

Funny you mentioned this, because this was my first thought after looking at the data OR you may have had a tranny shifting issue.

AT best, your fuel pressure seems erratic to me, this can cause your problem. My gut leans to a fuel problem, but it needs to be physically verified.

OK, I have some bad and good information. FIrst, on Wednesday on my way to the train station I had some serious issues. I had a blinking check engine light and bad hesitation at times. I immediately checked my codes and found a P0303. On Friday I pulled the ignition coil for #3 and found out that it was basically falling apart. It wasn't even 20K miles old as I replaced them all around 90k. Anyway I pulled all the bits and pieces out and replaced it with an older one I had. All the codes cleared. I also replaced my MAF with another one that they told me was the correct number. It seemed to run well but I noticed it smelled rich, sure enough when I ran a mode 6 it failed half the tests.

I finally replaced it back with the old MAF and ran all the tests. The car no longer is jerky but it still seems like it has a little light hesitation while under load with light throttle prior to shifting. In general it's much better though. Here's the results of the data you wanted. Not sure if you can see something else going on.

I'd really love to analyze the data, but I'll be away from my laptop for a few weeks.

When I can Ill post back

Paul

I also replaced my MAF with another one that they told me was the correct number. It seemed to run well but I noticed it smelled rich

How long did you run it with a new MAF? You would have to give it some time so the PCM re-learns the fuel trims and see if the rich exhaust smell goes away (which would be a good thing). If it stays smelling rich I would start suspecting fuel issues with a new MAF (provided it is sending good data to the PCM)

sure enough when I ran a mode 6 it failed half the tests.

Again, this would be time dependent on the PCM relearn.


After looking at all the data, which for the most part looks pretty decent( nothing stands out like a sore thumb), a few things I notice.

1. Possible Sluggish Pre-O2 Sensors. A scope is required to verify this. This will cause hesitation.
2. The Calculated Load seems unreasonably high at idle. (This is usually a MAF issue)
3. The Fuel Pressure Sensor is sending the PCM erratic info. Its either telling the truth, which would mean a fuel system issue, or it is not providing the correct info to the PCM. This will cause hesitation, rich/lean conditions.
4. The Idle seems a little low, which suggests vacuum leak on a MAF engine, however the fuel trims Do Not support this. A good throttle body cleaning may be in order.
5. The Idle RPM varies 130 RPM, which is quite a bit, it's "hunting" up/down. Fuel Regulation, Vac Leaks can cause this.
6. The fuel trims DO support an under-reporting MAF sensor.

It should be noted, most of the data that was recorded was missing either some LTFT info and STFT info, maybe a limitation of the Bluedriver and this makes it difficult to tell what the PCM is doing for Fuel Control.

I've attached a spreadsheet for you.

The new MAF was only in for a few days. Would you recommend that I put it back in and see what happens as I haven't returned it yet.

I was thinking that maybe some of the fuel issues were associated with a dirty fuel filter, unfortunately my car doesn't have a serviceable Fuel filter, I think you have to replace the fuel pump to change it. Let me know your thoughts and if you'd like any more data. I was thinking of just having my Pre O2 sensors changed out.

One more thing, something that I've always noticed is that whenever the compressor kicks on, which is often the engine shakes a bit. It's been like this for as long as I can remember. The Compressor runs very often as it uses it to remove moisture from the air. I can run another test with it turned off as there's an option to shut it off completely.

It would be nice to see some Fuel Trims with the new MAF.

I don't believe you have a fuel volume problem yet ( ie plugged strainer/filter), because the 02's stay pegged rich at WOT.

So, if you can do some testing with the new MAF, Record the Following;

1. LTFT 1&2
2. STFT 1&2
3. MAF ( Grams/Second)
4. Fuel Pressure (PSI)
5. Engine RPM
6. Calculated Engine Load
7. B1S1 &B2S1 Voltages
8. Throttle Position

This way I can compare it to the original data you sent, so grab an idle, 3000 rpm, and a normal test ride.

Its very possible you have a little culmination of issues going on, so far from what I've seen I'm leaning towards wonky fuel pressure readings.

If possible take one ride and just record;

Both Short & Long term fuel trim (both Banks) and rpm

I want to see some LTFT from bank 2, for some reason there isn't very much of it recorded.

Thanks