Thanks George


vic

 

You sound like you want formal printed guidance so that's what I put together for you. I'll be glad to help you with this further, let me know after you digest this service info. On the issue of a fourth "failed" MAF, that's approaching 0% probability. This is most likely a MAF system problem. I suggest that you exhaust the P0101 diagnostic instructions first.


George

 

George,

I have done more testing based on the service manuals info you provided me and thank you, I decided to buy the used service manuals you found on e bays. I did gag a little at the price of $300 for the 3 volume set.

one of the tests was to do a wot acceleration and check the maf readings—I did it while recording the data, indeed it showed maf readings in the neighborhood of 17 pounds per min ( 130 gms per sec). So I don’t think the p0101 is at that end of the spectrum. I haven’t had a chance to do much more testing.

However, I did get my fuel pressure gauge working and got some good readings on fuel pressure, also it hasn’t had any bad starting times even now with OAT down in the low 20,s.

I would love talk with you privately about your pre retirement experiences, as I suspect we have some similar experiences. If you worked for Harris semi, I did consulting for Harris Farinon years ago. I tried sending you a “private text message” but your in box was full.

regards,

vic

 

Yes, your WOT MAF reading is good.

1. What is it at idle?
2. Did you pass all of the other tests in the diagnostics?
3. Do you have any freeze frame data that shows any other parameters out of spec when you set a P0101 code?
4. Are you convinced that you have no vacuum leaks, exhaust restrictions, air horn leaks, fuel trim issues, TPS issues, Reference voltage/ground issues?
5. How about compression?

George

 

I have not done a compression test , my tester is more than 50 years old and probably not reliable. It is the old rubber seal type, which has to be hand pressed in the plug hole until you get 3 compression strokes. Very difficult at my age.

I do have some freeze frame data, which I’ll try to add in another post. I didn’t see any obvious error indications from it.

Your question about leaks is a good one, I’m not sure!!! But I have done brake cleaner spray tests all around the air input path, and I don’t have a smoke source to test for leaks that way. I’ve wondered if some path behind the maf is leaking, like through the pcv valve or the hose from bank 2, which has no way to block air other than to disconnect and plug with a rag or other means.

The evap I.m. has set so I don’t think their is leak from that source.
The EGR valve was replaced within the last 12 months, and the EGR I/m has been set so I assume it’s not a leak source.

as for your question about idle maf, it is a little low just as the a.c. Compressor turns off, but the freeze frame data occurs at 46 mph not any where near idle. But again it’s a manual trans and I think the inova 3160 reader has a delay in it which could be masking the exact time of the dtc occurrence. I.E. if it occurs during a gear change and the throttle is released but the tester sees it after the throttle is repressed after the clutch is released. Does this make any sense? Is the freeze frame timing only dependent upon the pcm and not the reader?

Have been so busy that I haven’t done all other suggested testing ( Dianne has to be driven to P.T. several times a week), but will let you know as I get that data.

vic

 

Hi George,

I have the freeze frame data, it was caused by a P0101 DTC. I know the stft’s look high ,but I replaced the old fuel spider using poppet valves with the newer design (ac delco) which has wires and a solenoid replacing the poppet valves at the end of the fuel lines in the intake port.
I know that old poppet valve data rarely exceeds 10% positive or negative.

I forgot to add that I test the TPS sensor every week or so and it is linear from either 0.3 % or 0.0% up to 100% . It seems to report the 0.3% when it is warmer, and 0.0% when it is colder OAT. I also watch the ECT versus when the system goes to closed loop, usually about 136 F for ECT.

Freeze Frame Data:

fuel system 1 & 2———-closed loop

calc load————41.1%

ECT——————168 F

stft. bank 1———neg 11.7%

ltft bank 1———neg 4.6%

STFT bank 2—-neg 17.1%

ltft bank 2———neg 4.6%

MAP—————18.3 inches Hg— don’t know how Snap on reports map

RPM—————2384

speed————41 MPH

MAF————-7.768 #/min—58.73 gm/sec

TPS————-32.1%

OAT was in the high 40’s or low 50’s.

 

Your fuel trims are too large. Bank 2 is just short of setting a code. What are they at idle and at 2500 rpm, in park, engine warmed up?

Large negative fuel trims indicated that the O2 sensors are telling the engine computer that the sensor driven fuel delivery is resulting in a rich mixture that must be corrected to lower emissions and save the cat. Most common causes:

High fuel pressure
Leaking injectors
MAF
Exhaust leaks
Compression issues
Misfire
Bad O2 sensor
Bad ECT sensor
Intake restriction


George

 

I’ll get you some data today,but my recollection is that they are reasonable while driving on the flats at 45 mph.

maybe the answer lies elsewhere than maf! But can you confirm my calculations for maf at 2500 rpm’s?

2500/2 times 262 cubic inches = 327.5K cubic inches of air per min. Air at my altitude should be about 34.7 micro pounds per cubic inch yielding 9.5 pounds per min at 100% volumetric efficiency. I don’t know what GMC considers a good number. My maf is reading 7.8 pounds per min at 2400 rpm’s.

Here are the fuel pressure readings after I got the pressure gauge working: at the rail.

time. Pressure

0. 60

3 min. 50

15 min. 50

20 min. 50+. It went up slightly

restarted the test by running fuel pump for 3 sec

21 min. 54

29 mim. 54


35 min. 54 psi

40 min Test terminated still 54.


I sure hope it’s not leaking injectors as it is a brand new ac delco fuel spider. Never seen a misfire issue on obd reader.

Will get data today, but you may not get it until late your time.

 

George,

I did the data you requested, I did it while doing 3 things at once so I hope you can read my handwriting. The data is the second two columns, and the ECT was just 7 degrees below max at idle. Also note that after dropping back to idle from about 2500 rpm’s, the fuel system went open loop for a few seconds, then went to CL. I think I read that the fuel system will return to OL under certain conditions like low ECT or cold O2 sensors.