Hi George,
I got anew ac deacons fuel spider today,and installed it. Fuel pressures are back up at real close to 60 psi. The new spider is a real pain to install, the lines are really stiff and it has wires down to the injectors making it difficult to work with. I also found and replaced a vacuum line that ( think goes to the evap canister) had a bad/ weak end. Test drove the truck after resetting all dtcs, and it looked like it was working great. Then after 5 miles, engine hot/ normal temps took foot off the gas going down a short hill and it did it’s quick jump stall then every thing was ok but it threw the p0102 code. Drivability was better than before in my opinion. Speed was about 45.

I’ve changed the egr valve, changed the iac about a year ago because of high idle engine speed at red lights.

got any suggestions.

vic

 

What was your fuel pressure leak down at 10 min after key on after the new spider?


George

 

I can’t give you an accurate reading as my gauge hose seal is split. I can hook up the gauge with rubber hose and hose clamps until I can get a new replacement. But I can say that the engine starts in 1 second like it did before all these issues. The gauge is leaking at the Schroeder valve connection.

vic

 

Engine off, unplug the MAF sensor, start it and go for a drive and see if the problem goes away. Any repair history on the MAF or its wiring/connectors.

George

 

Hi George,

I have cleaned and checked the pcm connectors today and about 6 months ago. As for the maf connections, I have nor checked continuity from the maf connector to the pcm connector because I don’t know the PIN numbers at the pcm. With key on engine off, I checked the 3pins at the maf. Center pin is connected to ground with a dvm reading of about .34 ohms, and the minimum reading with shorted leads is very close to the same— cheap dvms don’t do a good job on low impedance measurements. One out side pin reads 5 volts, the other outside pin reads 12.3 volts, with the battery reading 12.7 volts.

As for driving with the maf disconnected, drivability seems better, but still has a few lurches/ short misses. The ses light is on. The lurch seems to happen mostly about 45 mph then with a tps drop going down a hill like the down side of a freeway overpass. The rpm’s drop down from about 1500 to maybe 1000. At 65 you don’t notice it or it doesn’t happen.

With the maf connected and the pcm dtc’s reset, the truck is getting worse with more lurches per similar drives. I did try putting E Z Turn on the seal at the plenum to air box connection. If you haven’t used E Z Turn, it is a gluey thick grease that is fuel resistant and almost makes a gasket adhesive. I haven’t driven it yet with this fix attempt. STFT LTFT’s seem to be getting better closed loop.

The maf’s seem to run from 0.56 #/min up to 13 as I shift through 5 speeds usually at 3 to 4k rpm’s.

Does this give you any more clues?

 

Your MAF wiring:

1. Blk/wht wire goes from the MAF to engine ground
2. Pink wire goes to fused 12v power
3. Yellow is the signal output to the PCM which arrives at pin 31 on the computer

Yes check continuity on that signal wire while moving things around as well as the quality of that ground and 12v power. The proper check of your MAF output is the reading at idle and the max reading right before a full throttle 1-2 shift. Those things should all be checked because of your MAF code but the fact that the stumble still happens with the MAF unplugged says that something else is happening to cause this.

We need the 10 min leakdown fuel pressure when you get your fuel gauge straightened out.

Key on engine off, look at your TPS output while moving the throttle back and forth and make sure that there are no glitches.

What are your fuel trims at idle and 2500 rpm?

Do you have any freeze frame data with your MAF code?


George

 

Yes freeze frame data always comes up maf=0.257, first dtc usually comes up at 0 mph, and a second can happen at 15 or 45 mph.

however, I put my digital scope onto the 12 volt lead and the 5 volt lead at the maf. I took pictures of the results, not sure how to get them to you. But I saw spikes in voltage on the 12 volts ( actually 14) that went up to nearly 18 volts. They occur about 1 per 3 to 10 cycles of the 2.2khz square wave maf signal. Maf freq goes up as engine speed is increased no significant waveform changes with speed.

I took one of my 2.2 uf electrolytic capacitors put it on my probes across the 12 volt lead to ground. It didn’t show much wave form improvement, but it stabilize the live data readings significantly. Haven’t driven it with this temporary fix as yet, but will some time today. It may be that this new maf is susceptible to transient while a delco one is not!!

got suggestions on how to send pic from my cell phone to you?

while doing these tests I have inova 3150 connected to dlc and was running engine from idle up as high as maybe 3k rpm’s, and one time I noticed that the inova read 0.257 maf for about 3 to 5 seconds. This was before I tried my capacitor trick.

my best guess is the inova has a slow sample rate and it hasn’t shown that reading when I’m driving and my wife is reading data to me.

so my conclusions are that it either a brand new maf susceptible to transients or it the pcm getting tricked into reporting the 0.257 maf reading.

 

To confirm since you did not include units:

The freeze frame data indicates MAF = 0.257 #/min = 1.94 g/sec at idle? If I have that correct do you ever see that value in live data? What is the normal idle value? What is the max value at a full throttle 1-2 shift?

Please report g/sec from now on, that's our language here.

Does the 12v power to the MAF (connected, back probed, meter leads on pink and blk/wht), truck running ever look wonky on a digital meter?

George

 

12volts on the maf pin looks solid on my scope, except for the spike glitch. Here in Nevada, we have little corrosion problems on grounds or other conductors. The earlier resistance from the maf center pin( ground contact) to chassis ground includes wire to pcm and ground connections on the pcm back to the chassis ground. It’s good.

my calculator says 0.257 #/ min equals 1.94 gms / sec. I drove the truck an hour ago and it threw the p0102 code 1 time only, but during the drive I tried full throttle for 5 sec then idle throttle until I felt the stumble several times— each time the stumble occurred the OBDII tester showed 0.257 #/ min on the screen for about 2 seconds. I drove 8 miles at speeds between 25 and 70 mph. Drivability was worse mostly at speeds of10 to 20 mph in my drive way.

STFT and LTFT’s are staying around - 3% with an occasional jump to -10%. They are better than when I had the bad “new” fpr, but they can be unbelievable. As for maf readings, idle readings now are about 4.5 gms/ sec. But max at shift seems to be lower than they used to be. Maf=60gms/ sec. A few years ago they would go to 90 gms/ sec.

Since the maf seems to always go to 0.257 #/min, 1.94gms/sec. Every time the engine stumbles is it possible that the pcm has a corrupted memory location in its routines?

Its one of the craziest problems I’ve encountered.

 

Yes that full throttle shift MAF reading is too low. You either have a MAF problem, wiring/power/ground problem, a PCM problem or an engine breathing problem. Have you had a volt meter on the 12v supply to the maf when you get that low 1.9 g/s reading at idle? Was it solid? Did you check the continuity from the MAF back to the PCM yet? The fact that you still have the problem with the MAF disconnected says that there is a MAF reporting issue but thats not your only problem.

Fuel trims are reported with all 4 numbers because we need to add the STFT and LTFT together for each bank to get the picture and see if those totals change at 2500 RPM.

I have been here doing this for 15 years and have seen maybe two legitimate engine computer replacements that fixed the problem. Statistically speaking that's the last possibility and the failure being one fuel cell programmed value is winning lottery ticket territory.

George