Surging during warm-up then random misfire at idle.

[Georgeb]

It wants to run ok tonight. Here is a video of the vacuum guage on manifold vacuum.

 

[mistaake]

Did I read something about Bosch o2 sensors! Get those things outta there. They don't play nice with Chevy trucks!

 

[Georgeb]

Did I read something about Bosch o2 sensors! Get those things outta there. They don't play nice with Chevy trucks!

I dug through my reciepts. It is an NGK O2 sensor. Do they also cause problems?

 

[Georgeb]

It wants to run ok tonight. Here is a video of the vacuum guage on manifold vacuum.

So here is a link to the video. I couldn't upload from my phone so I had to wait till this morning. I want to do this with my better guage once I get it back.

https://youtu.be/I_brh5QT_5k

 

[Georgeb]

So I haven't completely ruled out an intake vacuum leak even though I have drenched it with carb cleaner and sea foam deep creep down both sided to the point its running off the engine. After keeping a close eye on the coolant level t seems to me to be using some ever, ever so slowly like maybe a cup in two weeks. If it's leaking it is evaporating so I cant find it. I don't smell it in the exhaust or otherwise and it doesn't smoke at all even on startup. I have heard of injecting propane into the crank case to find internal vacuum leaks but have never done it. It should be easy enough. Anyone have experience with this?

 

[HotRodPC]

Like this:

Yep, that's correct. The module gets power from the USB connection, so you just need ground and TX/RX to the ALDL port.

They are loaded into TunerPRoRT so it knows how to read the data coming from the ECM.

I should have known that! Will the free version of the software work for just the data logging/viewing I need to do?

Yep, the free version works great for data logging and diagnostics views.

WHATT !!! Now I know I want to go OBD1 TBI. I'm so sick of pumping the phuck outta the throttle and feather the pedal for cold idle take offs and ******** cuz I don't even feel like jacking and setting up choke. I'm almost jealous of my son's new 94 hoopty Dodge Ram 1500 4x4 w 225,000 miles. Thing sits over a week, he reaches in, doesn't touch a damn thing but the key and 1-2 revolutions it's running and he walks away.

 

[Georgeb]

Had some time this morning to run the truck through a warm up. When It started surging at idle I dissconnected the IAC and it didn't make any difference. Not sure what that means quite yet but it is another piece of the puzzle. I orederd thet adapter for connecting my PC to the OBD1 and will be plugging into it soon. At that point I can watch things more closely.

 

[Georgeb]

So I ordered the adapter to connect my pc to my truck and downloaded TunerproRT and all the files I need to connect and log data. After playing around with the software I am very excited to get it hooked up!!! Just waiting on my adapter so I can make my cable. Its coming from china so it will take a bit to get here. I can definatly see me tuning and burning new chips for this truck in the future.

 

[HotRodPC]

Should have it sometime this coming week huh?

 

[Georgeb]

I got it and have it working! check out the details on my other thread.
http://www.gmsquarebody.com/forum/showthread.php?t=13052

 

[HotRodPC]

So the end result to give closure to this issue for anyone who was following, did you get the problem fixed and what was it?

 

[Georgeb]

I did not get the surging fixed Now that I can read live data I was able to check and set my TPS to .49 VDC throttle closed and also verified the MAP output voltage with my hand held mighty vac at four different vacuum points. On my data stream I can see the rpm fluctuating, the vacuum fluctuating and the map voltage fluctuating all in correspondence with each other but I haven't figured out how it all fits together yet. The IAC was sitting at 90 steps most of the time and only moved one or two steps. Here is a snapshot of the problem area. It starts to smooth out around 90 deg F and the IAC begins to step down.

 

[Georgeb]

And here is a smoother idle at 95 deg F. It stays smooth like this from here on up. I haven's recorded a "cold" start yet but it idles rather smooth, then gets funky and then smooths out.

 

[Georgeb]

Here is an update. After working at getting my tps to read below five volts and checking the map sensor out. I recorded another log and with some help from a guy on the gearheads site it was determined that the iac counts were not where they were supposed to be at idle. It sat a zero steps so i made an adjustment to the idle stop screw to close the plates more. This got me to about ten steps on the iac. I also had the timing set to eight degrees advanced. Once I cpulled that back to zero mi iac steps went up to about fifteen. I recorded another log while driving hot and it was determined the mixture goes lean when I open the throttle and then recovers so I tested the fuel pressure. I had ten psi at idle so it was decided to try to raise the pressure a bit. I was able to crack the factort adjuster weld loose and turn the screw two turns which brought it up to twelve psi. the idle surge (only happens during warm up around eighty five degrees) is almost completly gone. I do however notice the engine seems to have developed a flat spot just off idle when taking off from a stop. If I give it more throttle it accelerates fine so I wonder if the fuel pressure is too high now. I ran without the egr with no noticable change in performance. I am going to try dropping the fuel pressure a bit and see what happens. The other thing I need to do is install bushings for the throttle shaft to reduce the play there. I am making progress!

 

[Georgeb]

Well, he flat spot seemed to increase and knowing there is debris in my tank I took the fuel filter off and back flushed it. WOW! that thing was loaded. Since I didn't have a new one I put it back on and will be picking one up after work today. On my drive to work this morning I noticed the flat spot has been reduced but is not gone. I should note the flat spot which happens around 8 - 10 % TPS position only happens when the engine is cold and goes away quickly as the engine warms. I have 12 PSI fuel pressure at idle even with a junked up fuel filter but that doesn't say anything for delivery or PSI while under load. Just may be running on the fine line of not enough fuel to satisfy the cold engine but enough when it's warmed up. Going to install a new filter and grab an extra for later. I do wonder if it's another component being flaky but I need to rule out fuel delivery first.

Edit: the gas does not come out of the tank like seen in the pic. This pic was of the contents of the filter flushed out. I am sure I didn't get it all out either.