I'm using WinALDL to capture data from an '88 GMC 1500 350 truck (747 'puter). When the truck is warm on a hot day (80°F+) it will all of the sudden die, but thru a slow death.

50K on a rebuild, and I watched the timing mark with a timing light while the engine was dieing and it was still getting spark.

Any suggestion. BTW the O2 sensor is original (200k) and engine is tuned and runs good.


Condenced data file for ease of readability.

Time IAC MAP RPM O2 BLM R/L cnt
20.9 51 28.8 900 0.239 133 2
22.1 51 28.4 925 0.305 133 20
23.3 51 28.4 925 0.248 133 38
24.5 51 28.8 900 0.239 133 56
25.7 51 28.8 900 0.265 133 74
26.9 51 29.2 925 0.239 133 92
28.1 51 28.8 925 0.243 133 110
29.3 51 28.8 900 0.248 133 128
30.4 51 28.8 900 0.265 133 144
31.6 51 29.5 875 0.208 128 148
32.8 52 63.5 350 0.194 129 148
33.7 52 63.5 350 0.194 129 148
34.9 113 84.2 0 0.186 128 0
36 145 84.2 0 0.186 128 0



Original data file

Time PROMID IAC Coolant SPEED MAP RPM TPS INT O2 Batt Knock BLM R/L cnt
20.9 9821 51 82.9 0 28.8 900 5.5 128 0.239 13.7 2 133 2
22.1 9821 51 82.9 0 28.4 925 5.5 128 0.305 13.7 2 133 20
23.3 9821 51 82.9 0 28.4 925 5.5 128 0.248 13.7 2 133 38
24.5 9821 51 82.9 0 28.8 900 5.5 128 0.239 13.7 2 133 56
25.7 9821 51 82.9 0 28.8 900 5.5 128 0.265 13.7 2 133 74
26.9 9821 51 83.5 0 29.2 925 5.5 128 0.239 13.6 2 133 92
28.1 9821 51 83.5 0 28.8 925 5.5 128 0.243 13.7 2 133 110
29.3 9821 51 82.9 0 28.8 900 5.5 128 0.248 13.7 2 133 128
30.4 9821 51 83.5 0 28.8 900 5.5 128 0.265 13.7 2 133 144
31.6 9821 51 82.9 0 29.5 875 5.5 128 0.208 13.5 2 128 148
32.8 9821 52 82.9 0 63.5 350 5.5 128 0.194 13.2 2 129 148
33.7 9821 52 82.9 0 63.5 350 5.5 128 0.194 13.2 2 129 148
34.9 9821 113 82.9 0 84.2 0 5.5 128 0.186 13 0 128 0
36 9821 145 82.9 0 84.2 0 5.5 128 0.186 13.1 0 128 0

 

What's up with the coolant temp looks like it suddenly got cold (if raw readings) or hot (if converted)
I would look at this first maybe replace the sender.

 

That's not temp, that's MAP readings...

It looks like there's a sudden shift in pressure.

I'm taking a stab at the interpretation, RPM drops, pressure should increase do to rpm count dropping, ie less vacuum.

Is this the changeover point to closed loop? Sounds like it doesn't want to idle meaning IAC should be checked. Trying to idle at 350 rpm sounds a little low.

 

Yup, I misread "speed" for rpm wnen following up the chart...

 

looks like a fuel problem... the o2 is confined to readings <.3 volts. Looks as though its going real lean and then dying. Should bounce all over the place somewhere between .1 and .9 volts as the comuter monitors and adjusts the fuel flow.

 

i suppose also that the o2 could be bad as well. I dont really know what they do when they go bad but i suppose it cvould give low readings and cause the engine to run real rich.

 

The enigne is idling fine (for minutes) and then it takes a dive. The throttle is at it idle setting (constant 5.5).

The O2 sensor is low but I'm getting about 18 L/R crossing. So that shows the O2 sensor is good. But again one should see some higher reading.

My BLMs are higher (130's to 160's through out the SD map) indicating my fuel map is lean. But if the O2 sensor is "flakey" this would affect BLMs.

I'm thinking the O2 sensor is tired. But on a WOT run I see the O2 voltage at ~.8 volts. So wassup???

Wide Avg BLM
RPM \ MAP 20 30 40 50 60 70 80 90 100
400 0.0 128.0 129.2 0.0 140.0 0.0 0.0 0.0 0.0
800 133.4 146.3 143.2 143.3 148.0 0.0 0.0 0.0 0.0
1200 135.0 143.0 152.9 151.6 143.8 0.0 0.0 0.0 0.0
1600 135.1 148.5 153.7 151.3 143.9 141.8 138.0 0.0 0.0
2000 137.3 142.9 146.5 145.5 141.6 139.6 138.0 0.0 0.0
2400 136.9 147.4 148.2 145.7 142.2 140.5 138.0 0.0 0.0
2800 134.3 158.5 159.0 153.5 134.1 131.0 126.0 0.0 0.0
3200 135.3 152.7 154.7 150.1 137.3 139.5 0.0 0.0 0.0
3600 0.0 156.0 150.5 146.2 136.3 0.0 0.0 0.0 0.0
4000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
4400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
4800 0.0 0.0 0.0 133.0 0.0 0.0 0.0 0.0 0.0
5200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
5600 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
6000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
6400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

 

I suppose you could just replace the o2 sensor. It is pretty old and a new one never hurts. It looks as thought eh engine is getting too much air (Huge major vacuum leak) or not enough fuel (could be many things). Is it possible to get some data of the truck doing this in closed loop when the engine is warmed up? It would be interesting to see what the computer does to react to the engine dieing down. From what you said, the computer is trying to compensate for thw lack, or apperent lack of fuel. Even though ive never heard of the injectors going bad on the tbi units i guess its always possible. The thing about it looking ok at wot probably means that its not your fuel pump. Im sure the other guys around here will have more ideas.

 

It's a lean condition. If anything you want to be richer than 14.7:1 at idle. The car will enter open loop at idle after a couple minutes and that's why you don't see the o2 cross counts moving. It's showing a lean problem, BLMs should be tuned for around 128, 126 is a good value but low 130's is fine and probably better for gas milage if you haven't enabled highway mode in the ecm.
So back to the lean problem, replace fuel filter, make sure injectors are getting enough pressure and then make the stock FPR into an Adjustable FPR. Increase the pressure until the BLMs go to 128, the open loop idle o2 volts should then be above 400mv.

 

Vehicle was in closed loop during the "test". The 83 temperature is in C or 181°F.

the O2 counts are increasing, just not when it is about to die.

 

if so then why isnt the intergrator coming up to compesate for the lack of fuel. Does anyone else see that as well? It looks like its stuck at 128.

 

dimented24x7 - very good point. There are about 18 Rich/lean crossings per data point and I perceive that as closed loop feed back. WinALDL had a check in the Closed-Loop "box" that says the computer is in closed loop. But you are right, the INT should be higher than 128 is the engine is lean.

So the INT should be changing if the 'puter was in closed loop.

 

I think you have a TPS problem but with 200k on the original O2 sensor i would change it out.

Lonnie

 

The engine is idling, so seeing non-varying 5.5 for a TPS reading is correct.

Also at WOT, the TPS would read 98.9, so the TPS is working. U might be looking at a wrong column. The hypertext web stuff won't put spaces in correctly.

 

TTT

 

Do you have a friend that has a truck with the same Throttle body and sensors?

It would be nice to swap it on and see if it solves your problem.

Keep us posted

Lonnie

 

It looks to me like the problem is with the O2 sensor. The values should be above and below .45. I have a similar problem. my O2 values fluctuate between .15 and .33 and the engine stalls. In my case, I have independant dual exhausts with no cats and the sensor mounted in the exhaust pipe. I plan to change to a heated sensor.

John