Intermittent O2 reading

[Dont fake it break it]

What are the IAC counts at idle now? Can you disable the idle bump up when the scanner is connected? The idle IAC count doesn’t matter if the idle is bumped up. I forget if that’s a prom programming or not but I can do it in tunerpro.

I actually wanted to try tuner pro but I wasn’t really sure how to get everything I needed. I hear it’s for an older operating system and you got a download this or that in order to make it work and it sounded more trouble than just buying a scanner. I have not yet figured out if it’s possible to disable the idle bump. Here’s what I just recorded.

About a minute later I got this one

And finally, do you have any idea what these are supposed to be telling me?

thanks!

 

[bp71k5]

View attachment 339765
I actually wanted to try tuner pro but I wasn’t really sure how to get everything I needed. I hear it’s for an older operating system and you got a download this or that in order to make it work and it sounded more trouble than just buying a scanner. I have not yet figured out if it’s possible to disable the idle bump. Here’s what I just recorded.
View attachment 339764
About a minute later I got this one
View attachment 339765
And finally, do you have any idea what these are supposed to be telling me?
View attachment 339766
thanks!

Other than the idle being high, looks ok in the first picture, gets pretty lean in the second.

tunerpro works fine on newer OS. Just install it, but a cable, get a few settings files and run a data log. That said, the scanner data is pretty clear it’s running lean so I’d not mess with tunerpro if you don’t need to. Gotta figure out why it’s lean, or whether it thinks it’s lean.

I’d let BigBlock72 help you out further, as he has helped me out in the past. Only thing o might suggest is to look at the plugs and see if they indicate a really lean condition. That might point you to whether there’s a vacuum leak making it think it’s running lean vs actually running lean.

Mines a retrofit tbi so I don’t use all the vacuum fittings on the throttle body, but the rubber caps always seem to degrade and crack after just a few months. You might try checking all those to make sure they aren’t leaking.

 

[bigblock72]

View attachment 339765
I actually wanted to try tuner pro but I wasn’t really sure how to get everything I needed. I hear it’s for an older operating system and you got a download this or that in order to make it work and it sounded more trouble than just buying a scanner. I have not yet figured out if it’s possible to disable the idle bump. Here’s what I just recorded.
View attachment 339764
About a minute later I got this one
View attachment 339765
And finally, do you have any idea what these are supposed to be telling me?
View attachment 339766
thanks!

Glad you figured out the IAC issue.

Seems a little odd the engine is at 1000 RPM but the IAC is only at 33 or 60 counts?

What scanner are you using? Some scanners will put the computer into aldl mode that forces the idle to 1000 rpm and will cause other weird issues. I wonder if that is possibly what is going with the fuel trim issue. The software engineer that set up these old computers apparently had an issue with illegal drug use. I have no idea why you would design something to change its behavior simply because someone is looking at what its doing.

Have you driven this without the scanner?? I wonder if it will run ok now that you fixed the IAC wiring.

Do you have the original injectors kicking around somewhere? I wonder if the wonderful chinese NAPA injectors are bad or have the wrong flow rate, probably should keep them around until this is straightened out.

 

[Dont fake it break it]

Other than the idle being high, looks ok in the first picture, gets pretty lean in the second.

tunerpro works fine on newer OS. Just install it, but a cable, get a few settings files and run a data log. That said, the scanner data is pretty clear it’s running lean so I’d not mess with tunerpro if you don’t need to. Gotta figure out why it’s lean, or whether it thinks it’s lean.

I’d let BigBlock72 help you out further, as he has helped me out in the past. Only thing o might suggest is to look at the plugs and see if they indicate a really lean condition. That might point you to whether there’s a vacuum leak making it think it’s running lean vs actually running lean.

Mines a retrofit tbi so I don’t use all the vacuum fittings on the throttle body, but the rubber caps always seem to degrade and crack after just a few months. You might try checking all those to make sure they aren’t leaking.

Yeah I replaced all the vacuum lines thinking I must have a leak somewhere although it did test 17-20 lbs At the throttlebody which I read was normal. Theoretically speaking, one of the things I’ve been trying to figure out is why would the computer think it’s running lean when it isn’t?

 

[bp71k5]

Swapping back to the old injectors might be a good option like mentioned above. Could also increase fuel pressure to see if the problem gets better. Both of those might point to something.

 

[Dont fake it break it]

Glad you figured out the IAC issue.

Seems a little odd the engine is at 1000 RPM but the IAC is only at 33 or 60 counts?

What scanner are you using? Some scanners will put the computer into aldl mode that forces the idle to 1000 rpm and will cause other weird issues. I wonder if that is possibly what is going with the fuel trim issue. The software engineer that set up these old computers apparently had an issue with illegal drug use. I have no idea why you would design something to change its behavior simply because someone is looking at what its doing.

Have you driven this without the scanner?? I wonder if it will run ok now that you fixed the IAC wiring.

Do you have the original injectors kicking around somewhere? I wonder if the wonderful chinese NAPA injectors are bad or have the wrong flow rate, probably should keep them around until this is straightened out.

Yeah kind of kicking myself for not following the step one in double check all your connections. Honestly I think it’s always idle that high and yes, I definitely have forward with the Bass idle adjustment screw. I follow the adjustment procedure end it ends up right there after putting it in gear between 600-700. The scanner is the Actron 9500. I hear you on the design flaw for sure. I had the WTF look on my face for about an hour when I realized it was actually preventing me in someway from resolving my issue by feeding me bad information.So I drove it last night and it ran fine but still picked up a lean code. And yes, I still have the old injectors. I didn’t have any real reason to think they were bad other than not being able to resolve the suspected fuel delivery issue. They were really the only thing I never replaced and so I figured what the hell. I actually never throw anything away on purpose. I could probably rebuild a junkyard motor with all my old, used, but probably still working parts.I’ve suspected a vacuum leak for sometime because while on the break at a long light, I will have to pump the brake once just to regain pressure. It doesn’t go straight to the floor or anything but if I’m on it for more than say 30 seconds, it will start to sink. .

 

[Dont fake it break it]

Swapping back to the old injectors might be a good option like mentioned above. Could also increase fuel pressure to see if the problem gets better. Both of those might point to something.

Swapping back to the old injectors might be a good option like mentioned above. Could also increase fuel pressure to see if the problem gets better. Both of those might point to something.

I hear you on that and will try it for the sake of ruling it out but my doubt is because I had the lean condition before I even began the rebuild. To recap, I’ve replaced rod and crank bearings But original cam and crank, rings but kept pistons and rods, rehoned cylinders, New pushrods and lifters, machined and rebuilt heads, Delhi plugs and wires, MSD coil and distributor cap, all new sensors and almost all new pigtails, New exhaust manifolds, new check valves on secondary air system, And now we built throttlebody.. and now we built throttlebody. Really wishing now I would have just sucked it up and gotten flow matched injectors for another 75 bucks but believe me when I tell you the bill was adding up on what was supposed to be a budget build. A point my girlfriend keeps reminding me of. LOL.

 

[dyeager535]

Disconnect your brake booster hose as close to engine as possible, plug it, and carefully go for a drive.

A leaking booster is a vacuum leak. It's got a one way valve on the hose, so it CANNOT bleed down if the valve is good, that leaves a leaking brake booster.

A test for the booster I've seen from GM manuals is to idle the truck in park, without touching the brake, for a couple of minutes. Leave the truck sit. Go back 45 minutes later, and without starting it, pump the brakes. You should get 2-5 vaccum assisted pedal depressions before you lose assist. If you dont, the booster or the hose to it is leaking and need replaced.

A leaking (internally) master cylinder will also require you to "pump up" the system when the pedal is depressed for long periods. When it finally let's loose and you are at an intersection, it's a bit scary.

 

[bigblock72]

Yeah kind of kicking myself for not following the step one in double check all your connections. Honestly I think it’s always idle that high and yes, I definitely have forward with the Bass idle adjustment screw. I follow the adjustment procedure end it ends up right there after putting it in gear between 600-700. The scanner is the Actron 9500. I hear you on the design flaw for sure. I had the WTF look on my face for about an hour when I realized it was actually preventing me in someway from resolving my issue by feeding me bad information.So I drove it last night and it ran fine but still picked up a lean code. And yes, I still have the old injectors. I didn’t have any real reason to think they were bad other than not being able to resolve the suspected fuel delivery issue. They were really the only thing I never replaced and so I figured what the hell. I actually never throw anything away on purpose. I could probably rebuild a junkyard motor with all my old, used, but probably still working parts.I’ve suspected a vacuum leak for sometime because while on the break at a long light, I will have to pump the brake once just to regain pressure. It doesn’t go straight to the floor or anything but if I’m on it for more than say 30 seconds, it will start to sink. .

A vacuum leak on a TBI system will generally not make it go lean because the MAP sensor compensates, the vacuum leak will however cause a high idle. Don't go too far down the vacuum leak rabbit hole.

I didn't realize the lean problem was happening before the engine rebuild, I'm wondering if this has the correct PROM in the computer. Pull the computer and check the code on the PROM itself and verify that it is for a 350. if it is then it might be time to just burn a chip for it and move on with life.

 

[Dont fake it break it]

A vacuum leak on a TBI system will generally not make it go lean because the MAP sensor compensates, the vacuum leak will however cause a high idle. Don't go too far down the vacuum leak rabbit hole.

I didn't realize the lean problem was happening before the engine rebuild, I'm wondering if this has the correct PROM in the computer. Pull the computer and check the code on the PROM itself and verify that it is for a 350. if it is then it might be time to just burn a chip for it and move on with life.

So the map sensor will compensate a vacuum leak by applying more fuel and therefore raising the idle? I get that and are you saying that the map sensor values in some of the snapshots of the scanner are within normal range?Also could explain 10 mpg but hell, it was only 14 mpg in 1987. The scanner shows a prom ID 4411, but I haven’t been able to locate a ID guide online for that vehicle.

 

[bigblock72]

So the map sensor will compensate a vacuum leak by applying more fuel and therefore raising the idle? I get that and are you saying that the map sensor values in some of the snapshots of the scanner are within normal range?Also could explain 10 mpg but hell, it was only 14 mpg in 1987. The scanner shows a prom ID 4411, but I haven’t been able to locate a ID guide online for that vehicle.

4411 is AFBX printed code for a L05 5.7l with M40 trans. It is the correct chip....Have you changed the distributor yet? I had one of these years ago that set lean codes and putting a distributor in it fixed the problem. I think the pick-up coil was weak or the module was freaked out. If the distributor doesn't fix it your only options are a new chip or raising the fuel pressure.

The idle is raised by the additional air from the vacuum leak, the MAP compensates because the vacuum level in the intake changes, computer doesn't care otherwise.

 

[Dont fake it break it]

4411 is AFBX printed code for a L05 5.7l with M40 trans. It is the correct chip....Have you changed the distributor yet? I had one of these years ago that set lean codes and putting a distributor in it fixed the problem. I think the pick-up coil was weak or the module was freaked out. If the distributor doesn't fix it your only options are a new chip or raising the fuel pressure.

The idle is raised by the additional air from the vacuum leak, the MAP compensates because the vacuum level in the intake changes, computer doesn't care otherwise.

Well good news on the chip I guess. No I didn’t change the distributor because I couldn’t find any real damage. The teeth looked good And it’s fun OK but that’s the extent of my knowledge about it. It’s not stock because I looked up the part number and I think I remember it came from AutoZone. I did replace the module and used the high temp grease on it. That would suck to buy a new dizzy after that and the rotor/cap but I will if it comes to it. Speaking of which, the only pigtail connectors that I did not change are the ones going to the module. I bought them but one doesn’t look quite right. I don’t suspect anything being wrong but it was more of a preventative maintenance thing. They stay plugged in even though the clips are broken but I couldn’t tell you more than that about them or their performance. By the way, I’ve got what I think might be a rod knock. Funny considering the new bearings but maybe one is in the oil pan and I just don’t know it yet. I’ve been meaning to take a look but wanted to resolve the other issues and get it smog first because I’m on borrowed time. Any chance that’s related? I’ve heard about knock sensors picking up noises like that and making adjustments to timing and such and I think I read that the computer will allow a predetermined amount of knocking or missing before it makes adjustments or something. Any thoughts on that?

 

[bigblock72]

Well good news on the chip I guess. No I didn’t change the distributor because I couldn’t find any real damage. The teeth looked good And it’s fun OK but that’s the extent of my knowledge about it. It’s not stock because I looked up the part number and I think I remember it came from AutoZone. I did replace the module and used the high temp grease on it. That would suck to buy a new dizzy after that and the rotor/cap but I will if it comes to it. Speaking of which, the only pigtail connectors that I did not change are the ones going to the module. I bought them but one doesn’t look quite right. I don’t suspect anything being wrong but it was more of a preventative maintenance thing. They stay plugged in even though the clips are broken but I couldn’t tell you more than that about them or their performance. By the way, I’ve got what I think might be a rod knock. Funny considering the new bearings but maybe one is in the oil pan and I just don’t know it yet. I’ve been meaning to take a look but wanted to resolve the other issues and get it smog first because I’m on borrowed time. Any chance that’s related? I’ve heard about knock sensors picking up noises like that and making adjustments to timing and such and I think I read that the computer will allow a predetermined amount of knocking or missing before it makes adjustments or something. Any thoughts on that?

The knock sensor can pick up engine noise but it will only affect timing it can not cause it to run lean. Try putting a new distributor in it, use your current ignition module as a spare since they do fail fairly often. The connectors on the module will not cause these issues, if they had a problem the engine wouldn't start or set a code 43.

 

[Dont fake it break it]

The knock sensor can pick up engine noise but it will only affect timing it can not cause it to run lean. Try putting a new distributor in it, use your current ignition module as a spare since they do fail fairly often. The connectors on the module will not cause these issues, if they had a problem the engine wouldn't start or set a code 43.

Fair enough, I’ll do it. Any recommendations??

 

[Dont fake it break it]

Disconnect your brake booster hose as close to engine as possible, plug it, and carefully go for a drive.

A leaking booster is a vacuum leak. It's got a one way valve on the hose, so it CANNOT bleed down if the valve is good, that leaves a leaking brake booster.

A test for the booster I've seen from GM manuals is to idle the truck in park, without touching the brake, for a couple of minutes. Leave the truck sit. Go back 45 minutes later, and without starting it, pump the brakes. You should get 2-5 vaccum assisted pedal depressions before you lose assist. If you dont, the booster or the hose to it is leaking and need replaced.

A leaking (internally) master cylinder will also require you to "pump up" the system when the pedal is depressed for long periods. When it finally let's loose and you are at an intersection, it's a bit scary.

Scary? When idling at 1800 that’s an understatement!!
Well a new 6 dollar check valve feels waaay better already! There’s also a canister looking thing on that vacuum line between the booster and the throttlebody. What is that? It’s not a check valve unless it’s broken. Definitely allows airflow both ways.

 

[diesel4me]

If it is a black plastic thing that resembles an old style universal gas filter,in between the hose from the intake to the booster ,it is probably the charcoal canister dewhickey GM uses to absorb fuel vapors,to prolong the life of the rubber diaphragm in the brake booster..

 

[Dont fake it break it]

If it is a black plastic thing that resembles an old style universal gas filter,in between the hose from the intake to the booster ,it is probably the charcoal canister dewhickey GM uses to absorb fuel vapors,to prolong the life of the rubber diaphragm in the brake booster..

Interesting, never heard of it. I figured that was the check valve and the one on the booster was just simply a fitting for the hose. Cool, one more potential vacuum leak. LOL.

 

[bp71k5]

Interesting, never heard of it. I figured that was the check valve and the one on the booster was just simply a fitting for the hose. Cool, one more potential vacuum leak. LOL.

theres also a black round sphere GM used on older trucks that’s a vacuum reserve. I bought an aftermarket version and it leaked fairly quickly so ditched it. Just beware.

 

[Dont fake it break it]

theres also a black round sphere GM used on older trucks that’s a vacuum reserve. I bought an aftermarket version and it leaked fairly quickly so ditched it. Just beware.

It took me years to figure out what that was. So I could pull that hose going to it and cap it off and have no ill affects?

 

[Dont fake it break it]

Also now while in park and I hold the throttle down steady at any RPM it will hold for a couple seconds then drops. Immediately comes back up and drops again. Over and over. Going to check the fuel pressure again but not sure what that is symptomatic of.
Fuel pressure is 13 - 14 after the filter.
TPS is good. 5 V reference signal. 14 V ground. Steady consistent increase and decrease with throttle even holds steady at any position with no fluctuation.