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InDeep****Now
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49 Posts
Discussion Starter · #1 · (Edited)
Hey guys, my name is Mike. I have a rebuilt 4.3 TBI in my 89 S10 Blazer, and was hoping for some advice on a CEL I've been getting here lately. First off, I'll give ya the specs on the motor:

Bored over .060
Sealed Power Flat top 350 Pistons
Mild Comp Cam (duration=215 lift=.500)
MSD ignition module and pro billet distributor
high flow FlowMaster exhaust
Plenty of air w/K&N filter
I'm pretty sure the compression ratio may be 9.7:1 even though the builder says 9.5:1

Everything else is stock on the motor. Injectors and all. At first, everything ran great, although, setting it at performance settings timingwise (37 BTC) at the beginning of the first build caused some issues with the crank, and had to rebuild it again. Second time around, everything went good. Initial timing is set around 10, and advanced is somewhere around 32 BTC. Anyhow, I just drove the truck from NC to TX and everything went fine until I crossed TX line. I have run nothing but 93 octane in it, and the problem I am now having is a CEL that indicates problems with TPS or O2 sensor, although both are brand new. It only comes on above 60 MPH. I am thinking this may be a fuel related issue. Any comments or suggestions are welcome. I am going to install an adjustable FPR soon, and hope that may help solve this issue, but I am being told I will have to have the ECM reprogrammed. Don't understand as everything went fine to begin with and was good for 4 months until I came to TX. Everything is running fine, I mean, smooth idle @750RPM no hesitation, nothing. Just the damn CEL.

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WFO
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5,030 Posts
What are the code numbers? No change in the way it runs from before to after the cel is on? Always start out by checking for vacuum leaks and/or exhaust leaks when you get an O2 code. As well as the wiring.
 

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InDeep****Now
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49 Posts
Discussion Starter · #3 ·
What are the code numbers? No change in the way it runs from before to after the cel is on? Always start out by checking for vacuum leaks and/or exhaust leaks when you get an O2 code. As well as the wiring.
No change in the way it runs at all. No vacuum leaks as well. All lines have been replaced with new. While over 60MPH, if I throw it in Neutral for a few seconds, then back into gear, it drops. Then 1 minute later, get the code again. I believe the code is 13. My truck isn't with me right now as I have it in the shop getting an alignment. I can tell you that I had to extend the O2 sensor plug wire using 12 ga. wire and butt connectors. After the lift was put on, it was nearly impossible getting the factory harness to plug in. Not enough reach. But the problem never occurred up until 4 months after that was done.
 

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10,722 Posts
I'm surprised it runs at all with a cam that big. TBI doesn't like big cams or anything out of it's operating range. I did this same thing on a 92 4.3 in my chevy truck only I used a smaller cam that was computer compatible. I also added venom injectors, adjustable fuel pressure regulator, fuel pressure check bung, all new sensors and a edelbrock chip. Even the intake is a edelbrock unit. For about 6 months the truck ran like gang busters, couldn't believe the power it had. Then it just went away and I couldn't get it back after countless hours of trying. Finally, something in the TBI system went bad I yanked the heads, slapped on a set of 98 Vortec heads and a intake for a Quadrajet. Hot rodded TBI systems to work properly have to be tuned on a dyno and custom chip burned for the new system to work properly. If your running stock injectors it's running so lean it's likely on the verge of burning a piston. I still have all my TBI stuff and it's for sale for cheap if you'd be interested just shoot me a PM.
 

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InDeep****Now
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49 Posts
Discussion Starter · #5 · (Edited)
I'm surprised it runs at all with a cam that big. TBI doesn't like big cams or anything out of it's operating range. I did this same thing on a 92 4.3 in my chevy truck only I used a smaller cam that was computer compatible. I also added venom injectors, adjustable fuel pressure regulator, fuel pressure check bung, all new sensors and a edelbrock chip. Even the intake is a edelbrock unit. For about 6 months the truck ran like gang busters, couldn't believe the power it had. Then it just went away and I couldn't get it back after countless hours of trying. Finally, something in the TBI system went bad I yanked the heads, slapped on a set of 98 Vortec heads and a intake for a Quadrajet. Hot rodded TBI systems to work properly have to be tuned on a dyno and custom chip burned for the new system to work properly. If your running stock injectors it's running so lean it's likely on the verge of burning a piston. I still have all my TBI stuff and it's for sale for cheap if you'd be interested just shoot me a PM.
Actually, it runs just fine. Lots of power. Has no problem turning those 33s over if I wanted. The cam puts all my torque on the lower end, and mid range rpm for climbing/towing. it's not all that big.
Send me a pm on what's for sale and how much. I don't see why the chip wouldn't work for the setup I have. But ya never know. On that note, I've been running this setup for about 10 months...
 

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10,722 Posts
I ran the timing around 6 degrees advanced and let the computer do the rest.
Here's my entire combo
Block bored .030 decked .010
Entire rotating assembly balanced.
Flat top 4 valve relief coated skirt pistons. 1.560 comp height.
.030 thickness head gaskets. Quench distance .043
Stock TBI heads with Ferrea necked down SS intake and exhaust valves.
Milodon double roller timing chain
Isky hydraulic roller cam Duration @.050 .204 Intake .209 exhaust. Made for low end torque and towing. Computer compatible.
Matching springs, locks and retainers. Comp cams 1.6 roller rockers, Magnum push rods, Crane roller tappets.
Edelbrock Performer TBI intake with matching computer chip
Venom fuel injectors. Adjustable fuel pressure regulator with vacuum compensator. Fully ported TBI unit. TBI Pod spacer.
MSD Blaster II coil and MSD spiral core spark plug wires.
Dual exhaust into turbo mufflers.
Getrag 5 speed transmission with Ram clutch and pressure plate.
3.42 gears with posi traction.
When this combo ran right I could tow a 21 foot gambler bass boat and you could hardley tell it was back there. When the wiring in the TBI system stopped working correctly I converted it over to Vortec heads and a carb.
I'm not telling you what I did on TBI being hard to tune just to be spiteful or anything else of the sort, I'm telling you based on experience plus what many other rodders on this site passed on to me. The TBI systems computer is very limited and it can't learn much more than stock. When you used the larger cam the vacuum went down, the TBI system don't like to see lower vacuum to the MAP sensor, when it does it starts to throw codes you can't get rid of, that's why it's recommended it be tuned on a dyno and a custom chip burned for it on the spot. Also the larger cam makes the EGR system work differently because it's seeing more exhaust gas than it would in stock form since the stock camshaft is painfully small. I learned really fast after I did the build the stock injectors still worked, but once it got past half throttle, power did not pick up any, no matter how much more throttle I gave it. It was running really lean and I got lucky it didn't cook a few cylinders.
 
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