Another SBC TBI Problem Thread (1 Viewer)

[jcj_78FJ40]

First thoughts:
Cam shaft is not correct for the TBI set-up.

This is a good point. TBIs often don't do well with performance cams. This site does a good job with explaining TBI and cams-http://tbichips.com/.

Do you know what cam you are running? What was the base timing for your Gen 1 motor before the conversion?

A suggestion would be to see what the base timing you have now (with the timing wire connected) and compare it to what it used to be before the conversion. If the current timing is later, advance it to what it used to be.

It seems like a lot of guys were running ~15 degrees base timing with a mild cam. Overheating and backfiring can be caused by late valve timing.

 

[RAYJON]

Double check the engine grounds, a dirty/floating ground can cause all kinds of issues..

You seem to have done and tested everything else,

 

[PadreCruiser]

This is a good point. TBIs often don't do well with performance cams. This site does a good job with explaining TBI and cams-http://tbichips.com/.

Do you know what cam you are running? What was the base timing for your Gen 1 motor before the conversion?

A suggestion would be to see what the base timing you have now (with the timing wire connected) and compare it to what it used to be before the conversion. If the current timing is later, advance it to what it used to be.

It seems like a lot of guys were running ~15 degrees base timing with a mild cam. Overheating and backfiring can be caused by late valve timing.

Thanks so much for your response. I do not know what the base timing was for my Gen 1 motor before the conversion. When I put on a new timing gear set and chain during Conversion 2 I set up the gear set to zero and then when I had everything back together I timed it to 0* with the plug undone. I am sure that when it was carbed it was much more advanced. It does seem to want to run better when I dial in some advance, but it doesn't like to start as much.

 

[PadreCruiser]

Double check the engine grounds, a dirty/floating ground can cause all kinds of issues..

You seem to have done and tested everything else,

I have checked all the grounds I am aware of. I also ran other grounds from the back of the passenger head to the frame and body, and from the front of the passenger head to the battery. I really wanted it to be a grounding issue. I am sure it is something like this that I have just passed over. In my dreams there is one wire in the factory harness that I was supposed to connect somewhere that is just drifting around and shorting.
Problems like this are what make the TBI in a box kits so appealing.

 

[PadreCruiser]

Are you sure you have the correct injectors? The 4.3, 5.0 & 5.7 injectors are the same size but have different fuel rates.

Also, did you swap out the HEI dist for a EST dist? The EST modules are known to be problematic.

I checked out the injectors yesterday and they appear to be 350 injectors (orange posts).

 

[PadreCruiser]

This is a good point. TBIs often don't do well with performance cams. This site does a good job with explaining TBI and cams-http://tbichips.com/.

Do you know what cam you are running? What was the base timing for your Gen 1 motor before the conversion?

A suggestion would be to see what the base timing you have now (with the timing wire connected) and compare it to what it used to be before the conversion. If the current timing is later, advance it to what it used to be.

It seems like a lot of guys were running ~15 degrees base timing with a mild cam. Overheating and backfiring can be caused by late valve timing.

I looked at the base timing today with the Cruiser warmed up and it is just past the timing marks on the advanced side (mine goes up to 12*) so I am eyeballing around 13-15*.

 

[jcj_78FJ40]

How does it idle?

I can't imagine you haven't checked this but did you make sure there aren't a couple of plug wires crossed?

 

[TwelveGravity]

My issue was not so much a backfire issue but sputtering and with every repair I did it ran better but all in all the biggest problem was the aftermarket fuel pump. I put a fuel pressure gauge on while driving and could see it hesitate at times. Once I replaced this and actually could pull a good amount of fuel it started acting up again. Come to find out that I was sucking crud into the fuel pick-up line that was cutting off supply. I cleared that & cleaned the tank the best I could and didn't have a problem with fuel after.
Are you disconnecting the timing advance when you set & check your timing?
These have a timing advance on them that you have to disable to get proper timing.

 

[terrx]

Thanks so much for your response. I do not know what the base timing was for my Gen 1 motor before the conversion. When I put on a new timing gear set and chain during Conversion 2 I set up the gear set to zero and then when I had everything back together I timed it to 0* with the plug undone. I am sure that when it was carbed it was much more advanced. It does seem to want to run better when I dial in some advance, but it doesn't like to start as much.

TBI swirl port heads are fast burn and require less advance than older SBC heads.

I looked at the base timing today with the Cruiser warmed up and it is just past the timing marks on the advanced side (mine goes up to 12*) so I am eyeballing around 13-15*.

So what is base timing set to? 0 or "13-15" ? Base timing refers to tan/black disconnected. With it connected, 13-15 sounds about right for idle. Max is around 30 +/- 5 and all in by 3K RPM IIRC. I believe the tan/black wire connector is in a different location on 94/95 trucks. It may be buried in the harness somewhere. Are you disconnecting the right one?

Assuming you have a 7747 ECM, what's the broadcast code? It would be on a label.

 

[PadreCruiser]

How does it idle?

I can't imagine you haven't checked this but did you make sure there aren't a couple of plug wires crossed?

I have checked the plug wires several times and numbered the ends to make sure I wasn't tricking myself.
It does idle pretty well. You can start it and it will run just fine. The problems don't present themselves until you try to accelerate quickly, then you get the backfire through the intake. The overheating seems to happen when driving for more than 10 minutes. Hmm, did I put the right fan on when I went to a serpentine belt system (which I believe is reverse rotation)? I will go check my blades.
The difficulty restarting when warm is still a problem too, but it starts great cold.

 

[PadreCruiser]

My issue was not so much a backfire issue but sputtering and with every repair I did it ran better but all in all the biggest problem was the aftermarket fuel pump. I put a fuel pressure gauge on while driving and could see it hesitate at times. Once I replaced this and actually could pull a good amount of fuel it started acting up again. Come to find out that I was sucking crud into the fuel pick-up line that was cutting off supply. I cleared that & cleaned the tank the best I could and didn't have a problem with fuel after.
Are you disconnecting the timing advance when you set & check your timing?
These have a timing advance on them that you have to disable to get proper timing.

I am wondering about the fuel tank. I am using my stock 68 FJ40 one and it has a pretty small stock junction in the hose at the side of the tank. It might have some crud in it too. That is a good recommendation.
Yes, I did disconnect the timing wire when I timed it, 0*.

 

[BrianSanDiego]

I might have missed it but did you say if you've installed an air/fuel mixture gauge? They aren't cheap (less than $200) but holy-cow it can save you some headaches. You'd know on-the-fly if you're fuel supply is good, correct injectors, air/fuel map, etc... Get that stuff eliminated and you'd know to focus in on the ignition.

 

[PadreCruiser]

TBI swirl port heads are fast burn and require less advance than older SBC heads.



So what is base timing set to? 0 or "13-15" ? Base timing refers to tan/black disconnected. With it connected, 13-15 sounds about right for idle. Max is around 30 +/- 5 and all in by 3K RPM IIRC. I believe the tan/black wire connector is in a different location on 94/95 trucks. It may be buried in the harness somewhere. Are you disconnecting the right one?

Assuming you have a 7747 ECM, what's the broadcast code? It would be on a label.

The base timing is set to 0* with the tan/black wire disconnected. The timing when warm and idling with the wire connected is 13-15*. The tan/black wire was indeed in a different place, it is in the glove box on mine, because it was so close to the computer.
I do not have the 7747 ECM, I actually have the 7427. This is the one that has the ESC incorporated into the computer. I will see if I can figure out the broadcast code. Is it on the outside of the computer or on the inside?
Thanks for your help.

 

[PadreCruiser]

I might have missed it but did you say if you've installed an air/fuel mixture gauge? They aren't cheap (less than $200) but holy-cow it can save you some headaches. You'd know on-the-fly if you're fuel supply is good, correct injectors, air/fuel map, etc... Get that stuff eliminated and you'd know to focus in on the ignition.

I did not install an air/fuel mixture gauge, but I do have a bluetooth engine monitor and I am logging my data on ALDLDroid. So, I do have access to the O2 data. On my last run my wideband O2 was putting out a reading of 10.0 (WB02 AFR). I am not sure if this is 10:1, if so, then that means I am running rich, right? The 10.0 doesn't seem to change with throttle, so I am wondering if the data stream is correct.

 

[PadreCruiser]

Update, I checked my fan, and I put the wrong fan on it. I used the original standard rotation 18" fan because it was in better shape and fit my shroud, but when I did my Conversion 2, I converted to the serpentine belt system which runs in a reverse rotation. I have the correct water pump from a 1995 on, it but that just happened by chance, and I didn't even think that the thing ran backwards.

I did not install an air/fuel mixture gauge, but I do have a bluetooth engine monitor and I am logging my data on ALDLDroid. So, I do have access to the O2 data. On my last run my wideband O2 was putting out a reading of 10.0 (WB02 AFR). I am not sure if this is 10:1, if so, then that means I am running rich, right?

 

[Alz Toy]

I did not install an air/fuel mixture gauge, but I do have a bluetooth engine monitor and I am logging my data on ALDLDroid. So, I do have access to the O2 data. On my last run my wideband O2 was putting out a reading of 10.0 (WB02 AFR). I am not sure if this is 10:1, if so, then that means I am running rich, right? The 10.0 doesn't seem to change with throttle, so I am wondering if the data stream is correct.

Do u have access to a laptop, that u could download tuner pro from moates, and check blm's ( fuel ratio ) while driving? Has perimiters to uncheck fault codes ( auto trans vs manual, etc ), that might give u a better idea whats going on. Can download free, to try. That, along with some chips and a burner would get u started to tuning your own. Good luck

 

[terrx]

The base timing is set to 0* with the tan/black wire disconnected. The timing when warm and idling with the wire connected is 13-15*. The tan/black wire was indeed in a different place, it is in the glove box on mine, because it was so close to the computer.
I do not have the 7747 ECM, I actually have the 7427. This is the one that has the ESC incorporated into the computer. I will see if I can figure out the broadcast code. Is it on the outside of the computer or on the inside?
Thanks for your help.

I'm not familiar with the 16197427, but the broadcast code would probably be on a label somewhere. Perhaps even inside it. You're looking for something that tells what exactly it's programming is. If it came from a 5.7L (L05 presumably) that's a help. Anyway, the base timing should be set to match the initial timing programmed into the EPROM, and you could look up / verify it knowing the broadcast code, rather than assuming it's 0* which we're all recommending and it may be incorrect. If you go with Moates and tunerpro, you can set it to whatever you want then set the base timing to match. You're pretty much locked into Moates since your harness for the 7427 has a different pinout than the 7747. Without knowing much about the 7427 I still think you'd be much further ahead with a 7747 converted to EBL flash but that's another subject. I suppose you could swap harnesses or re-pin connectors if you really wanted to, but sounds like you know what you're doing with the 7427 and making progress.

 

[BrianSanDiego]

I did not install an air/fuel mixture gauge, but I do have a bluetooth engine monitor and I am logging my data on ALDLDroid. So, I do have access to the O2 data. On my last run my wideband O2 was putting out a reading of 10.0 (WB02 AFR). I am not sure if this is 10:1, if so, then that means I am running rich, right? The 10.0 doesn't seem to change with throttle, so I am wondering if the data stream is correct.

If that 10.0 doesn't change at all then it's not giving you the correct readout. The mixture is going to vary quite a bit depending on the throttle position and load. Yes 10:1 would be very rich but it would run. You'd want around 12:1 for max power and 15:1 for max MPG, and beyond those extremes it won't run very well. I'm not familiar with Tuner Pro, but if it could somehow get a real-time display or at least a data log from your O2 sensor, it would go a long way towards sorting out the injection.
B.

 

[jcj_78FJ40]

I have checked the plug wires several times and numbered the ends to make sure I wasn't tricking myself.
It does idle pretty well. You can start it and it will run just fine. The problems don't present themselves until you try to accelerate quickly, then you get the backfire through the intake.

Kinda sounds like a fuel delivery issue. I had very similar issues from a clogged fuel filter. They can clog up quick when your messing with the fuel system. Are you using high pressure hose (ethanol resistant)between the tank and the pump? I have read that low pressure hose may collapse with the higher pressure pump.

As someone mentioned, see if you can rig up your fuel pressure gauge while you are driving.

 

[PadreCruiser]

Do u have access to a laptop, that u could download tuner pro from moates, and check blm's ( fuel ratio ) while driving? Has perimiters to uncheck fault codes ( auto trans vs manual, etc ), that might give u a better idea whats going on. Can download free, to try. That, along with some chips and a burner would get u started to tuning your own. Good luck

Thank you so much. I don't have a windows laptop, but my cellphone is connected to my data stream through a bluetooth ALDL dongle. I am running an app called ALDLDroid so I can have both realtime and recorded data. So, I should be getting the same info as through tuner pro. I am saving right now to be able to buy the equipment to burn through Moates, just not there quite yet, but I am looking forward to that. My understanding is that ALDLDroid can be used to provide the data to burn chips using Moates BURN2, but I have not personally verified this.
I have BLM (Block Learn Multiplier?) data and it looks like it varies between 105 and 135.