2F TBI w/cam rough idle/running rich (1 Viewer)

[Kalino_74]

Hey Guys, need a little help. I'm running a rebuilt 2F with unknown performance cam with a TBI conversion. Using all sensor including VSS. I have a rough idle and have to advance the timing quite a bit so it won't backfire through the TBI. Other than the rough Idle and rich conditions it runs really awesome and has tons of power. I could just leave it be but I really want to find the issue. I've read through countless hours of TBI threads on all the TBI forums and I'm still dumbfounded. I'm running stock astro van chip and I know if I want perfection I need to have a chip tuned for my exact application. I was just thinking someone might have someone might have gone through this already and maybe has some knowledge they could pass along.

After checking fuel pressure, wiring, injectors, O2 sensors and all other sensors I might have narrowed it down to the MAP sensor. Although I'm only throwing the MAP isn't throwing a code I did notice that I'm only getting 12-14 hg vacuum which I've read is on the low side. Thinking the computer is dumping extra fuel giving me the rich conditions code 45. I'm going to try and use a vacuum pump and see if it changes when pressure to say 20hg's. IF it makes a difference then that just might be my problem.

There also seems to be a lot of different chips used in various years of the S10/Astro van with the auto trans. Can anyone tell me what stock chip number they have had success with? (Example ADUL) If I can't figure this out I'm going to bite the bullet and go with the dymamic EFI set up so I can adjust the chip on the fly but I have to learn how to use the software and figure out what all the tables mean. Thank you in advance for you help.

 

[Downey]

Hard to trouble shoot from where I sit, but a couple things that come to mind real fast are:
(1) The MAP sensor has to match the ECU/chip, you could have a mis-match.
(2) What distributor are you using (i.e. what are your ignition electronics???).
(3) Best results we ever got during months of TBI testing with the federal testing lab at AAA was when we used a bone stock Chevy S-10 chip for an automatic tranny in the stick shift Landcruiser---don't ask why, I don't know

 

[White Stripe]

I installed a air fuel ratio gauge on mine. That has helped a great deal to pinpoint issues and dial it in. If the map sensor is lazy it won't throw a code, they do tend to go bad time to time. Also, make sure your TPS is adjusted correctly.

 

[Kalino_74]

Hard to trouble shoot from where I sit, but a couple things that come to mind real fast are:
(1) The MAP sensor has to match the ECU/chip, you could have a mis-match.
(2) What distributor are you using (i.e. what are your ignition electronics???).
(3) Best results we ever got during months of TBI testing with the federal testing lab at AAA was when we used a bone stock Chevy S-10 chip for an automatic tranny in the stick shift Landcruiser---don't ask why, I don't know

Downey thank you for chiming in. To keep everything the same I used everything off a 1989 Astro van for the exception of a heated O2 sensor. I figured I might need that due to running Mark's offroad header.

I'm using the modified 78-87 Toyota distributor

I purchase a ECM out of an 89 Astro van and I can't remember which prom was in it at the moment but It was the factory prom. Do you have any prom numbers that you all used in testing that was for the S10 or Astro van?

 

[Kalino_74]

I installed a air fuel ratio gauge on mine. That has helped a great deal to pinpoint issues and dial it in. If the map sensor is lazy it won't throw a code, they do tend to go bad time to time. Also, make sure your TPS is adjusted correctly.

White stripe that's a good idea to install a air fuel ratio guage, I will have to look into that for sure. I did adjust the TPS to I think .59 or .60. I read somewhere that was the correct perameter's but it could very from vehicle to vehicle. I bought spare sensors to have just in case so I've swapped out the MAP already to see if it made a difference. No luck. Tomorrow I will try the vacuum pump on the MAP and see if that makes a difference at idle. It runs awesome at all other RPM's, it just stubles at idle.

 

[White Stripe]

So it has a rough idle? Or it just stumbles off of Idle when accelerating?

 

[Kalino_74]

So it has a rough idle? Or it just stumbles off of Idle when accelerating?

I guess I would describe it as a rough idle. It would stumble and backfire through the TBI before I advanced the timing. Once I advanced the timing it has great throttle response. One think I noticed when timing it with the brown wire disconnected the timing mark would jump around on me. I figured it was due to it idling poorly.

 

[Downey]

All "matching" S-10 OR AstroVan components are alright, AND the MAP sensor must match your chip/prom. When testing we used GM chip #16082087. Might want to make sure the Pick-up coil inside your Dizzy is operating properly (since Dizzy modification), and have to make sure you did not loose "home base" when removing the vacuum and mechanical advance from you 1978-87 Landcruiser Dizzy..

Your 02 sensor works with the VSS to control those idle functions, but it sounds like you have both in play ???

 

[White Stripe]

I guess I would describe it as a rough idle. It would stumble and backfire through the TBI before I advanced the timing. Once I advanced the timing it has great throttle response. One think I noticed when timing it with the brown wire disconnected the timing mark would jump around on me. I figured it was due to it idling poorly.

Well if you have a chip with a timing curve made for a v6 chevy, your going to have to move the distributor around and try different distributor timing. V6 chevy has a different timing curve than a 2f. So your only going to be able to get it to run ok. If u do a ebl upgrade to the chevy ecu that will make it flashable and give u easier tuning.

 

[jcj_78FJ40]

After checking fuel pressure, wiring, injectors, O2 sensors and all other sensors I might have narrowed it down to the MAP sensor. Although I'm only throwing the MAP isn't throwing a code I did notice that I'm only getting 12-14 hg vacuum which I've read is on the low side. Thinking the computer is dumping extra fuel giving me the rich conditions code 45. I'm going to try and use a vacuum pump and see if it changes when pressure to say 20hg's. IF it makes a difference then that just might be my problem.

I think you are right on track with this. I had a 5.7 with a terrible idle surge and finally figured out it had 5.0 injectors installed. I figured it out by putting a Vacuum pump on the map sensor and a vacuum gauge on the TBI MAP port. I adjusted the vacuum on the map sensor until I had max vacuum on the gauge and the idle smoothed out. There was quite a variance between the (2) gauges so I knew something was off with the fuel delivery.

I expect your right. The GM ECM will be looking for 20hgs. If it's only seeing 14 then it will beat itself up trying to get it up to 20. Unfortunately, I don't think a "cammed" 2f will pull sufficient vacuum for a 4.3 ECM. It would certainly be a good first step If you can determine the max vacuum that your engine will pull at idle. If this is the problem then maybe the chip can be reprogrammed.

Another hint;
If you decide to try this, start by hooking your vacuum pump up to the vacuum gauge and make sure they are both reading the same values. I figured this out the hard way

 

[Kalino_74]

All "matching" S-10 OR AstroVan components are alright, AND the MAP sensor must match your chip/prom. When testing we used GM chip #16082087. Might want to make sure the Pick-up coil inside your Dizzy is operating properly (since Dizzy modification), and have to make sure you did not loose "home base" when removing the vacuum and mechanical advance from you 1978-87 Landcruiser Dizzy..

Your 02 sensor works with the VSS to control those idle functions, but it sounds like you have both in play ???

I made sure to purchase all new sensors for the same vehicle that way I didn't get them mix matched but I will look over them again to make certain. I've rechecked the pick up coil and my gaps to make sure they are in spec. I modded another GM HEI dizzy that I had used on another project and I had the same results. So I'm thinking my dizzy is good but I won't rule it out. I do have a heated O2 sensor as well as the VSS.

 

[Kalino_74]

I think you are right on track with this. I had a 5.7 with a terrible idle surge and finally figured out it had 5.0 injectors installed. I figured it out by putting a Vacuum pump on the map sensor and a vacuum gauge on the TBI MAP port. I adjusted the vacuum on the map sensor until I had max vacuum on the gauge and the idle smoothed out. There was quite a variance between the (2) gauges so I knew something was off with the fuel delivery.

I expect your right. The GM ECM will be looking for 20hgs. If it's only seeing 14 then it will beat itself up trying to get it up to 20. Unfortunately, I don't think a "cammed" 2f will pull sufficient vacuum for a 4.3 ECM. It would certainly be a good first step If you can determine the max vacuum that your engine will pull at idle. If this is the problem then maybe the chip can be reprogrammed.

Another hint;
If you decide to try this, start by hooking your vacuum pump up to the vacuum gauge and make sure they are both reading the same values. I figured this out the hard way

That's a good idea to hooking up the vacuum pump to the vacuum gauge. I'm thinking if the MAP is the culprit then I will have to go the EBL route so I'm able to tune it. I'm just going to have to teach myself how to do it. I'll let you know the results of the vacuum pump test.