Map Sensor and one other engine question

[jokershockey29]

Hey everyone, i have an 87, with a 350 with TBI. I have swapped map sensor, coolant temperature sensor swapped vacuum lines from map sensor. The tuck has no oxygen sensor because the previous owner installed headers and just cut the wire from the oxygen sensor and i can't seem to trace it so i can install a new one. On to the problem.. the vacuum line i installed is clear and i have noticed that there is gas in the line at the carb. any clues as to what would cause this or if its normal? I have no idea. Second problem is, the truck runs well, but after a bit of driving the engine begins to lope. if you let off the gas, no loping, if you hit the gas. no loping. It only happens when you are just cruising. I notice the rpm's jumping on the tack so i don't think its a trans problem but i really have no clue. Any help would really be really great. If you need more info just ask. Thanks guys
Brian.

[heavychevy79]

You need to restore the O2 sensor back to the system first, before going on a wild goose chase for querks, that may have been caused from having no O2
sensor anyway.

The stuff in the vac tubes could be crankcase gasses or steam.

[pig rig]

with no 02 the ecm thinks the engine cylinders are cold and its trying to lean it out and adjust your timing

is your tbi bolted to the intake or does it have a performance spacer in between and is your map in the factory location
if so try raising your map up

[rfmaster]

Make sure that MAP is mounted above the TB vacuum inlet with its inlet port pointing down. MAP sensors are damaged by moisture - this is the reason for such mounting requirement. What you are seeing are gas fumes - manifold mixture air+ gas.

In 1987 trucks used a single wire O2 Sensor. When switching to headers it is highly advisable to install a three or four wire heated O2 sensor (AFS-74). O2 sensor needs to be heated to about 600F for it to begin to function ie produce voltage. Headers run at much lower temperatures then cast iron exhaust manifolds. PO in his lack of knowledge cut of O2 wiring without realizing that O2 is an integral part of engine control system, which explains lousy performance. Also, see if you have trouble codes set (you should ) by shorting pins A and B of ALDL connector.
Look for purple wire (O2 sensor feed) in the wire loom which goes to Pin D7 of the ECM connector. For more info check out TBI retrofit thread.

//RF

[Damien]

Your truck runs well when it is cold, because the engine is running in open loop and ignores the O2 signal until the engine is up to temp. Once the engine is up to temp, it should go into closed loop. Your PCM is looking for the signal. Not finding the signal, it is running rich. This will wash cyclinder walls causing premature wear and dilute your oil with gas. I would look into getting a three wire O2 sensor as rfmaster said. One wire is your signal to the PCM, one goes to switched power, and the other is ground.

[jokershockey29]

alright thanks everyone for responding. My TBI does have a spacer between the carb and manifold so i will check the height of the map sensor first. What I'm seeing in the line is actual fluid sloshing around so hopefully that will fix that problem. I'll have to look into the 3 wired 02 sensor. I'm going to have to get the mig welder out and weld a bolt in the header somewhere because there is no hole for an oxygen sensor. Thanks for all the input and if any other ideas come up i would really appreciate it. Thanks again!
Brian

[Desert1957]

Originally Posted by jokershockey29

Hey everyone, i have an 87, with a 350 with TBI. I have swapped map sensor, coolant temperature sensor swapped vacuum lines from map sensor. The tuck has no oxygen sensor because the previous owner installed headers and just cut the wire from the oxygen sensor and i can't seem to trace it so i can install a new one. On to the problem.. the vacuum line i installed is clear and i have noticed that there is gas in the line at the carb. any clues as to what would cause this or if its normal? I have no idea. Second problem is, the truck runs well, but after a bit of driving the engine begins to lope. if you let off the gas, no loping, if you hit the gas. no loping. It only happens when you are just cruising. I notice the rpm's jumping on the tack so i don't think its a trans problem but i really have no clue. Any help would really be really great. If you need more info just ask. Thanks guys
Brian.

I'm a little confused , you said you have "TBI" but in the same posting your mentioning a carb? was that a typo? or are you refering to the throttle body? Anyway , I have an 87 with TBI all factory wiring , If you need wiring diagrams or pictures of something let me know , I will be glad to help....

PS: the posting about running in "Open Loop" is right on. these engines will run like Dog-sh*t without an O2 sensor hooked up...

Desert

[jokershockey29]

yeah i was just referring to the throttle body. I am having a hard time tracing the old wire for the oxygen sensor. I'm concerned about seeing gas in the vacuum line to the map sensor. I'm hoping its not a vacuum leak somewhere in the throttle body.

[jokershockey29]

well its been a while, but just an update. I installed a 3 wired sensor and the truck runs better. But, after a while i'm still getting an 02 sensor error. I have checked voltage and the ground and it all seems right. I have tried 2 different sensors and its the same with both. I'm not sure what to do now.

[rfmaster]

Which Error code are you getting ???

13 Oxygen sensor failure - output remained at 0.35-0.55 volts for more than 2 minutes after warm-up. Possible broken or burned O2 sensor wire.

44 O2 sensor reads < 0.250 volt for over 20 seconds while operating closed loop - mixture is running lean.

45 O2 sensor reads > 0.550 volt for over 50 seconds while in closed loop with engine running over 1 minute and throttle open more than 2% - Rich mixture.

//RF