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Help! Brain teaser for tuning gurus

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Wingnutt

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Well folks, the TBI fight continues. Finally got ALDL configured correctly and WOW! Lost of information, but it has me stumped. Here are the symptoms:

Surging idle (700-900prm).

Stinking rich idle.

Popping in exhaust during initial warm up along with black smoke (mixture waaaay to rich).

Hesitation when throttle is quickly opened.


Win ALDL data:

IAC readings: 40 no change at idle.
O2 readings: 0.03 to 0.80v bouncing all over the place.
RPM: surging from 700 to 900.
TPS: steady at .50v
Temp: 185 degrees

Flag data:

Idle/cool (at 185 degrees?)
DRP occured (wtf is DRP?)
Closed loop mode (huh ?)
Rich flag (no joke)
BLM enable (what is BLM?)

Error codes: (I disconnected the battery for 5 minutes before logging the data)

42: Electronic Spark Timing (EST)

44: O2 lean


That O2 reading has me stumped. If the engine is running rich, why am getting an O2 lean code? Also shouldn’t the IAC be doing something at idle? Like adjusting the mixture and maintaining a steady rpm? Also why is it in closed loop mode? With the temp at 185 degrees, shouldn’t it be out of closed loop mode? This is getting on my last nerve, can anybody help? /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/dunno.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/thinking.gif /forums/images/graemlins/dunno.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/thinking.gif /forums/images/graemlins/dunno.gif /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/1zhelp.gif TIA.
 
With all of that in mind, I would start with replacing the O2 sensor. It seems that if it is reading lean and still smoking black it is sending an erroneous lean condition signal to the computer which is trying to compensate by dumping fuel in. I don't proclaim to know jack about Injection though so maybe somebody else can help.
 
cybrfire, right on with your diagnosis.. the o2 sensor is causing an erroneous lean reading into the computer, hence compensating by adding more fuel.. replace the O2 sensor and it will get better!
 
Thanks y'all. That was my line of thought too, but I figured I would check with somebody a lot more knowledgable than me before I started blindly replacing parts.

Amybody wanna take a stab at the rest?
 
on the est code, has the little tan(?) wire that you unhook for setting timing hooked up? If it comes unhooked code 42 sets and without that it could f up ur timin and make it rich.
 
I checked it when I double checked the timing, gotta disconnect it so you can accuratly check the timing. That's why I'm stumped.
 
im willing to bet that EST code may be from when you set the timing before and you just now get it because it only happened once and did not reoccur to set the light..
 
Try replacing the egr valve. That thing can do some pretty weird stuff to TBI engines. My egr was bad, and my truck did all sorts of crazy mess. The idle was sporratic and would jump up and down, sometimes it would run ok, then sometimes it would backfire/sputter and die. Hope this helps.
-Harrison
 
[ QUOTE ]

DRP occured (wtf is DRP?)


[/ QUOTE ]
DistributorReferencePulse
I sure hope that DRP's are happening when the engine is running...
 
Ok lots of things to check, thanks. Does anybody know where the knock sensor is loacted?
 
Dont worry about the knock sensor with a code 42. Code 42 has nothing to do with the KS.
A bad pickup coil or Dist module or bad ground can set a 42.
42 is also set when you disconnect the wire to set the timing.

Replace the 02 the readings are way out of specs.

Yea when the engine is warmed up you should be in closed loop. In closed loop the ECM uses data from the 02 sensor to controll F/A mixture.
When cold the ECM operates in open loop.And pretty much uses a pre set program and a timer.

Do your problems start after the engine is warmed up?
If it runs fine when cold and gets worse after it warms up. I would strongly suspect the 02 sensor.
 
[ QUOTE ]
Ok lots of things to check, thanks. Does anybody know where the knock sensor is loacted?

[/ QUOTE ]

It is in one of the drain holes in the block, probably on the passenger side. It will be almost all the way down by the oil pan, side of the engine, dead center, just above where the pan bolts on.
 
Thunder,

I had the open/closed loop thing bass ackwards. Thanks!

It is runing way to rich when cold and gets better as it warms up. Hopefully it's the O2 sensor. HOWEVER, it was running OK with that crappy old factory TBI on it. Could it have hidden the bad O2 sensor?
 
With the ALDL hooked up.
What is the coolant temp sensor (CTS) reading when the truck is cold? Does it increase as the truck warms up?
When the truck is fully warmed up the CTS should read the normal operating temp somewhere around 185*-195* at idle.

Also cycle the TPS thru its range.It should go smoothly from .50V to somewhere around 5 volts at WOT. Do this with engine not started and Key on. I think you can do this test with ALDL. I can with my scanner.

**edit**
You mentioned it ran ok with the stock TBI. Are you running a diferent TBI now? Is it a POS Holley? If it is you prolly have leaky injectors.
 
Yea it's a Holley (the second one) and it's doing the same thing the first one did. I had a friend stop by last night with a '90 that has the same TBI on it and his runs great, although he paid to have his tuned for his truck (wadda a wuss!).

The Holley tech guys seem to think it's the fuel presseure, and I specifially asked them about the IAC count not moving at idle while the O2 reading said rich then lean (no response below 2200rpm or so) and he said that either the O2 sensor or the IAC could cause that. Sounded like he was reading from the troubleshooting guide.

I'll check the CTS cold tonight. I've checked the TPS and the voltage rise is smooth from 0% (0.5v) to 100% (4.6v).

Since the general concensis is a bad (origional with 150k miles) O2 sensor, I'm gonna pick one up tonight and see if that helps.

Of course by now I'm d@mned and determined to get this thing working correctly.

Thanks again!
 
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