1990 Suburban TBI idle issue

[PurfsMcGurfs]

I don't think that a .030 over 5.7 is his problem. We had a 5.7 rebuild bored .030 10/10 crank in a '89 k2500 and it ran good until it lost a headgasket due to a shit head install.

The TBI system is different between a 5.7 and a 454 so it's a possibility that one had more room than the other. It's been a while but, I remember a lot of TBI trucks and TPI cars needed a new prom after mods like cams because of the map. OP says he has a different TBI, so he should swap that first and adjust the tps. That way it can be eliminated and it's either fixed or he'll need to figure out the cam specs. Everything else is basically new so it's down to the ECM or the TB. I hope it's the TBI, getting a prom for an unknown cam could be a bitch.

 

[M92PV4U]

Details so far:

• 1990 gmc v1500, tbi 5.7/700r4, 5.38 gears, ord 6" lift w/ shackle flip, 35" tires

The TBI system is different between a 5.7 and a 454 so it's a possibility that one had more room than the other. It's been a while but, I remember a lot of TBI trucks and TPI cars needed a new prom after mods like cams because of the map. OP says he has a different TBI, so he should swap that first and adjust the tps. That way it can be eliminated and it's either fixed or he'll need to figure out the cam specs. Everything else is basically new so it's down to the ECM or the TB. I hope it's the TBI, getting a prom for an unknown cam could be a bitch.

 

[Winchested]

Just have to datalog it with an al/dl to USB via laptop and send the bin files to tuner. It's fucking old tech so not many people doing it anymore.

Bill Hamilton Fuel Injection does it for us in the IH world.

454 had bigger injectors in the TBI compared to the 5.7. And fuel maps are likely completely diff.

 

[M92PV4U]

TBI CHIPS Home

TBI CHIPS Home

harristuning.com

 

[PurfsMcGurfs]

Oh, fuckin dumb. haha. I've been looking at suburbans with 454's lately for parts. It just auto applied in my brain since this thread was from a while ago.

 

[vrtillman]

Cool. I picked up an aldl so I can datalog since I for sure don’t have a clue what cam is in this. I’ll start reaching out to tuners and see what my options are. I looked into tuning these old bastards and it doesn’t seem to be as straightforward as what I’m used to with Hptuners. Like linux vs windows.

 

[ANGRYBLACK]

Cool. I picked up an aldl so I can datalog since I for sure don’t have a clue what cam is in this. I’ll start reaching out to tuners and see what my options are. I looked into tuning these old bastards and it doesn’t seem to be as straightforward as what I’m used to with Hptuners. Like linux vs windows.

I'm not sure of the ecm numbers but iirc there are a few Fwd car ecm's that you can use in place of what you have. The prom holds all the maps so you just have to swap in your old prom. If you need an ECM I have an 89 454 TBI ECM .

Iirc the difference in actual throttle bodies between the 454 and all the rest is bigger injectors and it flows 670 cfm unlike all the rest of them.

If you need an ECM mine is available. My injectors are frozen so it's all junk to me but good spare parts for another

 

[vrtillman]

I'm not sure of the ecm numbers but iirc there are a few Fwd car ecm's that you can use in place of what you have. The prom holds all the maps so you just have to swap in your old prom. If you need an ECM I have an 89 454 TBI ECM .

Iirc the difference in actual throttle bodies between the 454 and all the rest is bigger injectors and it flows 670 cfm unlike all the rest of them.

If you need an ECM mine is available. My injectors are frozen so it's all junk to me but good spare parts for another

I thought prom chips were 1 map/chip. Mine's a stock ECM & prom as far as I can tell. I reached out to harris tuning to see if he can work some magic without knowing cam specs and just datalogging. If that doesnt work, I'll hit you up since it might be a while before I can get the time to pull a junkyard motor and swap it in.

My brain is also telling me there's a fuel pump issue as I get a random misfire on acceleration which leads me to believe it's not getting enough fuel during WOT

 

[PurfsMcGurfs]

I thought prom chips were 1 map/chip. Mine's a stock ECM & prom as far as I can tell. I reached out to harris tuning to see if he can work some magic without knowing cam specs and just datalogging. If that doesnt work, I'll hit you up since it might be a while before I can get the time to pull a junkyard motor and swap it in.

My brain is also telling me there's a fuel pump issue as I get a random misfire on acceleration which leads me to believe it's not getting enough fuel during WOT

The prom will only have 1 map file on it. You'll have to swap proms to change mapping. Later EFI had more range in it's a/f mapping but TBI was primitive tech. If you can get a datalog it's not a bad idea to post it here, someone might spot something.

Misfire in acceleration could be fuel related but you had a new pump and filter so I'd look at the TBI unit first. Did you already try swapping the other TBI? That was the priority over the prom.

 

[ANGRYBLACK]

I thought prom chips were 1 map/chip. Mine's a stock ECM & prom as far as I can tell. I reached out to harris tuning to see if he can work some magic without knowing cam specs and just datalogging. If that doesnt work, I'll hit you up since it might be a while before I can get the time to pull a junkyard motor and swap it in.

My brain is also telling me there's a fuel pump issue as I get a random misfire on acceleration which leads me to believe it's not getting enough fuel during WOT

No problem. How old are your injectors? Sticking injectors was my problem. It misfired badly and had hardly any power.

 

[vrtillman]

The prom will only have 1 map file on it. You'll have to swap proms to change mapping. Later EFI had more range in it's a/f mapping but TBI was primitive tech. If you can get a datalog it's not a bad idea to post it here, someone might spot something.

Misfire in acceleration could be fuel related but you had a new pump and filter so I'd look at the TBI unit first. Did you already try swapping the other TBI? That was the priority over the prom.

I replaced it with the stock tbi fuel pump. I've got another on the way thats for a vortec moter since apparently those pumps put out more pressure. I've also got a 14lb regulator spring on the way which I'm going to put in the new tb since apparently low fuel pressure can be the root for a lot of problems.

No problem. How old are your injectors? Sticking injectors was my problem. It misfired badly and had hardly any power.

Injectors look fine, no visible drips or leaks and the spray pattern looks normal. I might pick up some spares at the junkyard if I can find time to get over there

 

[Winchested]

I replaced it with the stock tbi fuel pump. I've got another on the way thats for a vortec moter since apparently those pumps put out more pressure. I've also got a 14lb regulator spring on the way which I'm going to put in the new tb since apparently low fuel pressure can be the root for a lot of problems.


Injectors look fine, no visible drips or leaks and the spray pattern looks normal. I might pick up some spares at the junkyard if I can find time to get over there

Have you actually monitored the fuel pressure? Mine was maxed out at 12-13 psi but never had any issues.

 

[Cheepin]

Just have to datalog it with an al/dl to USB via laptop and send the bin files to tuner. It's fucking old tech so not many people doing it anymore.

Bill Hamilton Fuel Injection does it for us in the IH world.

454 had bigger injectors in the TBI compared to the 5.7. And fuel maps are likely completely diff.

454 also had bigger bores. I'm using a 454 TBI on a 406 with a small cam. No tuning and it runs fine.