*Need Help* TBI 489 running lean????

[Russ]

I could really use some help figuring out the fuel needs for the engine in my 88 crewcab dually. Specs are:

489 CI, 9.7:1 Compression
Edelbrock 6047 aluminum heads (110cc chamber, 290cc port, 2.19/1.88 valves)
Edelbrock 3764 TBI intake
Comp Cams XM262H camshaft (duration @.050": 218/224, Lift: .505/.515, Lobe seperation: 112)
CFM Tech over-bored 454 Throttle Body, adjustable fuel pressure regulator
Hedman Hedders
180 degree thermostat
3 wire O2 sensor

I have just recently put this engine in the truck and am in the process of trying to tune it. It starts up and idles fine. I put all new sensors on the engine when I built it and everything reads correctly on my scannner. My concern is that when I bring the rpms up to about 3000-3500 and watch the O2 sensor output, it initially starts climbing to about the .7 to .8mv range and then after about 15 seconds it starts dropping to the .2 range. The engine starts to cut out around the same time. The engine also speeds up when I let off the throttle. If I am interpreting this correctly that is telling me that I am running very lean? I did replace the fuel filter with no difference.

I am running the stock chip in the computer. I have done a lot of reading about the TBI and everything I read tells me something different. I had read that the stock computer should be able to compensate for up to a 15% increase in engine size. I am well below that at about 8% increase. But obviously I have improved the airflow through the engine, so I do not know if that is causing the lean condition.

I spoke with a fella named Brian at TBICHips.com yesterday and he is telling me that I need to replace both in tank fuel pumps with a higher capacity pump as the stock pumps will not be able to keep up with the engine. I am currently running about 15psi fuel pressure. If I replace the pumps how do I regulate the higher pressure? Is there someplace I can get a higher pressure spring for the regulator? I am using the stock regulator, I just modified it to make it adjustable.

He is also telling me that I need a custom chip for the engine.

I am not trying to build a race engine. I just want a good strong engine to be able to tow with. I am starting to think I may have gotten in over my head with this throttle body.

I apologize for the long post, but I have been fooling with this for a few weeks now and am running out of ideas. Any help would be greatly appreciated.

Russ

 

[HarryH3]

A stock TBI 454 only made around 250HP , so the program doesn't provide nearly enough fuel for your new engine. It isn't just the size of the engine that you need to be concerned with. The power output has a much bigger impact on the fuel requirements, especially with EFI. Those heads have made a BIG change in the power the engine will make, as has the cam. A different cam will also change the vacuum curve of the engine, which has a major effect on the MAP sensor. The MAP sensor is one of the major inputs used by the ECM to determine fuel requirements.

I'd start with looking at larger injectors, possibly higher flow fuel pump, and definitely a custom chip that is programmed to match the engine requirements and the injectors that you end up with. To get it running perfectly will require lots of datalogging time and probably several tweaks to the programming. Since you plan to tow with this rig, it will be VERY important to datalog the air/fuel ratio while pulling a heavy load. If the engine runs lean while towing it can melt the pistons.

 

[Russ]

I'll be honest with you, you are talking to someone who has trouble figuring out how to turn a computer on. I am no electronics wizard by any means. When you say data-logging? is that something that will require me learning how to burn chips? I am not adverse to learning, but am in the crawling stage right now when it comes to the EFI stuff.

I am running the 80-85lb hr (every site I look at has them listed differently) injectors now. Is there a bigger injector that I can run?

Thanks for the help and any more info you can give me will be greatly appreciated.

Russ

 

[HarryH3]

You're going to need to do a LOT of reading. A good place to start is over at http://thirdgen.org/techbb2/ Don't just go there and start posting questions, they'll flame you into orbit. Start reading the DYI PROM, and TBI forums and you'll start to get some ideas about what is ahead of you.

Unfortunately, computers are incredibly stupid devices. They will only do EXACTLY what they have been programmed for. Your stock 454 TBI computer is programmed to provide the correct air/fuel ratio under any circumstance, but ONLY to a stock 454. Your new engine has lots of changes, yet the computer knows nothing about them. It now has to be programmed to "know" how much fuel to deliver at a given temp, RPM, throttle angle, engine vacuum, etc. There are lots of variables involved, which the computer is recalculating millions of times each second.