1st TBI Conversion Help Needed

[MtBraun]

Here's my thread from Gearhead EFI. Thought I'd post here to see if anyone has thoughts.

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?6859-First-Conversion-Help-Needed!

Scroll to the end of the thread that explains my current problem and what I've done. Thanks in advance!

 

[1987 GMC Jimmy]

It sounds like it's in field service mode, which is really weird because that can only happen when it's on. It can't reflect FSM when the engine's off. I'd check to make sure the wire for your diagnostic circuit that goes to the ALDL isn't grounded somehow and/or somewhere.

 

[MtBraun]

I ended up scrapping the DIY cable in favor of one from AFI. Need to reburn my chip to eliminate ESC, and once that's back I'll try to fire it up.

 

[4WDKC]

Did you do the Zif socket and sf512 chip mod?

 

[MtBraun]

Did you do the Zif socket and sf512 chip mod?

I don't know what that is. Please elaborate.

 

[MtBraun]

I got everything hooked up and it starts and idles really nice. We took it for a long drive and it seems to have an off idle (maybe 1000 rpms) stumble or dead spot. It sometimes will die. Other times you can feather your way through the dead spot. Once its past the dead spot the engine seems to run really well. I suspected it may be due to the TPS, and tested the base setting at .59. There is no dead spot in the TPS as I slowly open the throttle. It does only go to 4 volts at WOT whereas I thought it should be closer to 4.5. But I'm a little stumped on the dead spot. All the searching I've done suggests a problem with the TPS. Thoughts?

 

[1987 GMC Jimmy]

Hmm, that doesn't sound right. I'm thinking 4.5-5V. It's been a while since I played with my TPS sensor, but I know the one that I have on right now is a cheaper replacement. It maybe a good idea to invest in a higher quality part when you do get a new one. That idle voltage is within spec but higher than I like to see, as well. I bored out the holes on mine to tilt it so it'd be as close to .5V as possible. I think I got it to .51V if I remember correctly, and it was at .59V initially. I would just get a new one because of the funky numbers.

 

[4WDKC]

I don't know what that is. Please elaborate.

Thats a no you havent dotn the mod. The chip burning equipment for a stock style tbi chip is expensive and only works 1/3 of the time. Installing a newer style socket to the circuit board in the ecm allows for use of a newer style chip that is cheap and works everytime. If you can solder you could make the mod yourself or contact Dave W. on gearhead to see if he will mod it for you.

I dont see any information about the engine, your stumble could be not enough fuel causing a lean condition.

 

[4WDKC]

Hmm, that doesn't sound right. I'm thinking 4.5-5V. It's been a while since I played with my TPS sensor, but I know the one that I have on right now is a cheaper replacement. It maybe a good idea to invest in a higher quality part when you do get a new one. That idle voltage is within spec but higher than I like to see, as well. I bored out the holes on mine to tilt it so it'd be as close to .5V as possible. I think I got it to .51V if I remember correctly, and it was at .59V initially. I would just get a new one because of the funky numbers.

those voltages are what mine were before modding also

 

[MtBraun]

Thats a no you havent dotn the mod. The chip burning equipment for a stock style tbi chip is expensive and only works 1/3 of the time. Installing a newer style socket to the circuit board in the ecm allows for use of a newer style chip that is cheap and works everytime. If you can solder you could make the mod yourself or contact Dave W. on gearhead to see if he will mod it for you.

I dont see any information about the engine, your stumble could be not enough fuel causing a lean condition.

I'll check out the mod, but I've had several email convo's with Dave W and he hasn't mentioned the circuit mod. From everything he's told me my setup should work fine for a stock application.

I suppose I could get the cable, download Tunerpro and log some data. That should tell me right away.

I checked all vacuum lines and the TBI base gasket with starting fluid and I don't get any sign there is a vacuum leak. No EGR to hassle with either.

 

[MtBraun]

[QUOTE="
I dont see any information about the engine, your stumble could be not enough fuel causing a lean condition.[/QUOTE]

I tested fuel pressure at the filter only since the fuel pressure regulator does not have a test port. I have 12.5 psi with key on and running. I did the fuel pressure regulator rebuild kit anyway. The injector spray pattern appears uniform.

 

[4WDKC]

Wait you have a stock chip and no egr?
What about A.I.R. pump/tubes?

If you dont have these installed and are using a stock chip the ecm is expecting to see these items to function and changes the tune to operate with them, without their input the truck doesnt have the right calibration to run correctly. For example the ecm could enable the air just off idle to give clean readings to pass emissions in a stock vehicle. Not a problem when the AIR is there but when removed the ecm is expecting to see the correct reading at the o2 sensor, without the fresh air the doesn't know its not getting the fresh air and thinks its an overly rich condition when its not but, it still pulls fuel trying to get the voltage right causing your stumble.

 

[MtBraun]

Wait you have a stock chip and no egr?
What about A.I.R. pump/tubes?

If you dont have these installed and are using a stock chip the ecm is expecting to see these items to function and changes the tune to operate with them, without their input the truck doesnt have the right calibration to run correctly. For example the ecm could enable the air just off idle to give clean readings to pass emissions in a stock vehicle. Not a problem when the AIR is there but when removed the ecm is expecting to see the correct reading at the o2 sensor, without the fresh air the doesn't know its not getting the fresh air and thinks its an overly rich condition when its not but, it still pulls fuel trying to get the voltage right causing your stumble.

Sorry for the confusion. My chip has been re-burned to eliminate EGR, AIR, and knock.

 

[4WDKC]

Having knock removed can be dangerous, definitely get you a scanner or a cable for a laptop so you can see the live data.

 

[MtBraun]

I changed out the TPS and it seemed to drive MUCH better. We still need to drive it some more but hopefully I have this nipped. I was able to get the base TPS setting to .54 and figured that was close enough. And I figured out why it would only go to 4.0 volts at WOT. The linkage from the donor vehicle must have had some more room in between the throttle body and the mounting bracket, because on this truck the plastic sheathing is preventing the throttle plates from opening all the way. Should be an easy modification and we don't plow snow at WOT so no rush. While I was checking things I pulled plugs 1-3-5-7. They are below, from left to right. Not sure what is up with 7. These plugs have about 100 miles on them.

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