samana76

Hello everyone. After two months of having my 951s in the shop for a head rebuild (with all original Porsche parts imported from Germany) and some other minor issues (see thread here: https://rennlist.com/forums/showthre...errerid=124230) I finally picked her up this past Thursday. I was really looking forward to going for a long drive this weekend but had to give-up this idea as the car is behaving a bit erratically.

Following are a few issues I have encountered these past three days in using her to which I hope I can get some insight from you much more experienced users.

The most worrying problem, and I think the culprit for most if not all the other problems, is the A/F mixture. Yesterday I hooked the A/F gauge and was astonished by what it was indicating. Please see the video here:


As you can see, at idle, the mixture bounces up and down a bit, but when I press the accelerator and lift off the needle goes down to 12 and then for a second or two it jumps up to 18 and then back to bouncing around the 14 mark. I am not very knowledgeable about this but it seems to me to be a very erratic behavior. Please also note that I had to have the head rebuilt because I burnt an exhaust valve in the second cylinder due to overheating issues, which was caused by lean mixture (this is what my mechanic told me).
What could this be caused by and how can I correct the issue, if it is indeed an issue?

Another issue, which I think is linked to the A/F one, is that there is slight idle hunting. You can hear the engine RPM go up and down a little and the idle needle very slightly hunting around 1000 RPM, but mostly you can see the oil pressure needle bounce. Please see the videos below:



Before I had burnt the exhaust valve and had the head rebuilt the idle was absolutely dead still (although a bit high at around 1200 RPM) and the engine hummed at a constant rate.
What could be causing this issue?

Again, another worrying issue is that there is a strong smell of exhaust fumes in the cabin now. It is so intense that it is nauseating. I don’t know if this is due to something not being tightened well. I don’t hear an exhaust leak anywhere and don’t smell the fumes in the engine bay, so I don’t know where it is coming from.
Any ideas where I should be putting my attention to correct this problem?

Finally, these past mornings when I started the car, a puff of smoke would come out from the exhaust. Just a grey puff when first starting the car in the morning. When starting it during the day after I had used it I did not notice any smoke. This might still be linked to the A/F issue.
Any suggestions regarding this issue?

Of course I will take the car back to my mechanic this week, probably tomorrow, but I would like to be aware of are the possible causes for these issues so to better discuss the problems and solutions with him. In the end I spent nearly $4000 between parts and labor for the head rebuild and minor issues and did expect to have a car that performed (and smelled) at least as good as before the problem occurred. I am quite disappointed at the moment, although I am sure everything will get sorted out – I just have to postpone my plans for my long (1500 mile) drive for another weekend.

I hope this post is not too long and I would truly appreciate all comments and suggestions regarding each issue.

Thank you all in advance.
Igor

Jeff N.

On your A/F ratio, you need to re-run the test and record the results under boost. Blipping the throttle and then seeing the A/F spike lean for a moment is not a problem. If you are at 18:1 ratios under boost, you absolutely have a problem.

The exhaust fumes are due some sort of exhaust leak. You need to take it back to the mechanic and ask them to check all the exhaust fittings for leaks. It's likely that something is not correctly assembled in the exhaust manifold area.

Idle hunting could be due a slight vacuum leak in the intake plumbing. Oil pressure is fine.

lart951

The wb readings are ok, 14.7 @ idle, it will go down as you accelerate to an optimal 11:3-11:7 under boost. Once you let go of the gas it will lean up for seconds and comeback to normal

dmcampbell

Yes, vacuum leak. If fact at idle, you should see close to 20 inches vacuum. O2 looks fine, but need to observe under boost in the 11's. Mike

Tom M'Guinn

Not sure how accurate that AFR gauge is, but it appears to be running around 14:1 rather than 14.7 as it would in closed loop mode. That would mean it is getting too much fuel (or too little air) at idle. Maybe that analog gauge just doesn't read that accurately, but assuming it's new and accurate, that's a clue on the surging idle. I go back to my post 27 in that other thread -- didn't sound like your issues were coming from a valve that burned out overnight -- sounds more like something in your engine management system is the culprit.

So, when the car was running fine before it started acting up, was the A-tune installed and working fine? Or did the problems start with the installation of the A-tune? Assuming A-tune was fine for a while, and assuming that AFR gauge is accurate, then I'd start by tracking down why the motor is rich at idle -- bad temp sensor, bad 02 sensor, bad AFM, sticky injector, clogged air filter, etc. If it started with the installation of the A-tune, then go back to stock to confirm it works fine in stock mode, then work with Rogue to figure out your issue with the A-tune installation.

Exhaust smell is a different matter altogether. It's almost surely unrelated to the engine management issues, but does not speak well of the shop to give it back to you like that. By the way, did you ask for the old valves back? You are entitled to get old parts back for this very reason -- to confirm they were really in need of replacement.

As for the AFR moving around, that's a normal pattern. The injectors are turned off completely when the engine is above about 1600 rpms and the throttle switch is closed, so your gauge will go full-lean in that circumstance, and will get richer when you hit the throttle etc. For steady-speed light cruising, look for 14.7. For WOT, look for something in the 11-12.5 range.

Other than A-tune, what else is non-stock on your car?

mikey_audiogeek

Exhaust smell in the car is usually due to the rear hatch not being closed properly.

eman930

Wow $4,000 for a head job? That seems really high, It's times like this Im happy Indo my own work.... your A/F looks good to me, Yoir idle issue is most likely due to a vacuum leak, Check the lines, Exahust smell could be a loose exhaust fitting, Or the rear hatch seal is bad and letting exhaust in, Check it out

samana76

Thank you all for your informative comments.

Indeed the A/F gauge indicates 14.3 at idle and never really gets close to 14.7. Also, I tried putting the FQS back to the default setting of 0 (Rogue_Ant suggested to move it to the number 2 setting a while back as I was getting a lot of 'popping' from the exhaust when lifting off after accelerating hard on track) to see what happens and I noticed very little difference at idle between the two settings. With the FQS at 0 the A/F gauge indicates 14.0, while at 2 (-3% fuel) it indicates 14.3

Regarding the vacuum leak, I could not find it anywhere. I checked all the tubes in the engine bay and sprayed starter fluid around the injectors, intake manifold, exhaust manifold and the various vacuum junctions but it would make no difference to the RPMs. In any case I will tell my mechanic to look into this.

Finally I checked the rear seal and it seems to me to be sealing very well, so I don't think it is that. I will tell my mechanic to recheck all the exhaust fittings as well.

x Tom M'Guinn Thanks for your detailed message. In addition to the A-Tune the upgrades I did are: Fabspeed performance exhaust package (3.0" maxflo mufflers with deluxe tip, catbypass with downpipe, and turbo outlet pipe), Pauer Tuning TiAL 38mm wastegate, Lindsey Racing manual boost controller with autometer Boost gauge, Innovate Motorsports Air Fuel Ratio gauge with wideband controller and oxygen sensor, NGK BPR7ES spark plugs, MSD Blaster 2 Ignition Coil.
The A/F gauge and sensor are new and recently installed so I do believe the gauge is accurate. When I installed the A-Tune the car ran fine for about two months. I tracked it and, although I was having the exhaust 'popping' issue (https://rennlist.com/forums/showthre...errerid=124230) it was running great - steady RPM at idle, no fumes in the cabin, strong engine. Unfortunately I did not have the A/F gauge hooked up, so I cannot say if there was indeed a problem which I was not aware of.
I will discuss the mixture problem with my mechanic. What I am starting to find strange is that it is too rich even after I reduced the fuel by 3% by turning the FQS to the #2 position.

Thank you all again for all your help and support with these issues. You are all great as always.
Have a good evening everyone.
Igor

INURGRL951

If you had a digital type gauge you would see it spike also it is just strange to see it on a needle type gauge like something has gone wrong.

samana76

Here's an update on the situation:

I got the car back a couple of days after I brought it in. The mechanic told me the air/fuel mixture reading on his instrumentation was correct and the idle was fine as well. However the odor of exhaust in the cabin was due to oil being burnt. He said that this had something to do with a PCV valve which was corrected (I don't think I understood this correctly however as I checked online and could not find any information regarding PCV valves in the 951). In any case the odor had almost completely gone away (a little is still present, I can smell it especially when stopped at a red light/stop) and the engine was running much smoother, so I was content with the picking it up.
This was last Thursday morning.

I drove the car maybe a hundred miles between Thursday and Saturday. I monitored the A/F gauge constantly and this is what I found:

At idle, after warming the engine, the gauge indicates 14.3, never more.
Cruising the gauge indicates 14.3, never more.
Full open throttle the gauge indicates 12.
On lift off of accelerator it pegs at 18 for a few seconds.
And now the really strange one, after a drive, even a short one, at idle the gauge indicates 13, never more. When I cruise it goes back to 14.3.

So the numbers are a bit off. However since the mechanic said that with his instrumentation the numbers are normal, I'm thinking the calibration of mine is a little off, although I really don't understand the difference in idle.

Then Saturday evening when I started her up to head back home the low oil warning light came on. I had to add 2 quarts of oil to bring it back to its maximum level! This is very odd as the oil had been replaced and topped off just recently (note that there are no visible leaks).

I did not drive it on Sunday.

Today it was running fine for maybe 80-100 miles, then as I was driving down a hill I let go of the accelerator and the exhaust started popping like crazy. When I pressed the accelerator again the engine started to run really rough - it was running on 3 cylinders! I think one of the spark plugs got fowled up in the decent. The indicated A/F mixture was 13.3. Luckily I was very close to the mechanic and so I drove it straight to him and am now writing these little adventures on this forum from the bus station.

I guess my questions at this point is, can anyone suggest a tuning shop knowledgeable in 944 Turbos in the bay area or even a bit farther where I can bring the car. I think my mechanic might not have a thorough knowledge of this particular model and can't pinpoint the problem.

Thank you all for taking the time to read and give me your opinions and suggestions.
Igor

URG8RB8

Igor:

If your mechanic told you that you have a problem with your PCV valve and he corrected it, you are in big trouble because:
A. He is a liar
B. Obviously knows nothing about these cars
C. Your $4K head job is probably all screwed up

Sorry for your troubles, but you need to find a better shop. Did you speak to Tom and Crazy Eddie about a good local shop? I have used CT Automotive (Campbell) in the past, when I was too busy flying around to do it myself. They are expensive but know the car very well. Everybody that works there owns and drives Porsches including two 951's. He has been there over 25 years which says something. Tony is the owner and the best mechanic is Ryan.

Tom M'Guinn

Some random thoughts...

I think you are wise to find a new mechanic. Your car does not have a PCV valve, so if your mechanic is telling you there is a problem with the PCV valve, he is at best wrong.

Did you ever get back the valves he claimed burned out (overnight)?

You seem to have a combination of problems with the car, some of which may be related to his work. Did you have low oil pressure before the work? The main pulley bolt needs to be torqued properly after the head gasket is replaced, or you can have oil pressure issues. I have to wonder if he has the 944 flywheel lock needed to torque the pulley bolt correctly?

If the oil burning smell is gradually going away, it may be due to oil spilled on the exhaust when the head gasket was replaced. Either way, hitting the recirc button on the dash helps keep engine bay smells out of the cabin.

Based on his other comments, if your brand new wideband is showing 14.3 at idle, I would believe that over a claim that his "instrumentation" is showing proper readings. It should flutter above and below 14.7, in "closed-loop" mode, and it does not sound like it is doing that. Sounds like it is running rich at idle and about right at full throttle. The 18 AFR when you let off the gas is normal. I'd be inclined to look at the fuel pressure regulator and the vacuum line that controls it to start.

I've always done my own work, so can't really give first hand feedback on local mechanics. Tony Heyer in Mt. View has always had a good reputation, but he does not seem to be a big fan of working on modified cars. Where are you in the Bay Area?

reno808

what the head decked?

Rogue_Ant

...these cars do not have a PCV valve. Perhaps he meant the AOS (air oil separator), but that is a red-flag.



Engine air fuels are dynamic. They will change, depending on what is being asked of the engine.
Under idle and part-throttle cruising, the computer attempts to target around 14.7. It does this by dithering around 14.7. The AFRs will swing a little richer, then a little leaner - with the average ideally being 14.7.
Full throttle can be anywhere from 13 to 11, depending on how much boost pressure, and rpm.
If you lift off the accelerator, then the DME turns off the fuel injectors completely until the engine RPMs come down to ~1500rpm. During the injector-off RPMs, your AFRs will read maximum lean (18 in your case). This is absolutely normal.
Additionally, the WBO2 sensor/gauge has a latency. Its display/data will always be slower than what is actually happening.

Your idle/part-throttle sounds a slight bit rich, but nothing really concerning. Check fuel pressure. With the car idling, remove the vacuum line to the FPR. Fuel pressure should be 43.5psi (3bar). It is fairly typical for aftermarket 3bar regulators to run a bit high. If the fuel pressure is high, then that would explain the slightly rich condition.


This is a concern - oil is going somewhere. I highly suggest checking the AOS hose connection, and make sure you mechanic did not incorrectly install it.
Additionally, burning oil will skew the WBO2 reading, and probably shorten its life.


This is also concerning. As I mentioned earlier, if you let off of the accelerator, the computer turns off the fuel injectors. With no fuel being injected, there should be no exhaust popping (the only thing in the exhaust should just be air). It sounds like you might have an injector that is/has failed...
This would explain the burnt valve (if that is so), and the exhaust popping. You should really pull the spark-plugs and take a look at what is going on.

samana76

Thank you all once again for your very valuable input.

The car is still with my mechanic. I haven't heard anything from him yesterday but hope to have an update today. In any case as soon as I get it back I will do the checks suggested (fuel pressure, AOS hose connection) and will take it to a specialized 951 mechanic as suggested (Tony Heyer in Mt. View or Ryan at CT Automotive in Campbell).

I'm located in Burlingame and am willing to drive even far to reach a very knowledge mechanic that can really sort my car out. It would be great if they had a dyno to run it as well. So if anyone has any other mechanic/tuner to suggest I would appreciate this input.

Thanks.
Igor