I have a 1990 chevy 350 truck that I put an edelbrock intake and a 670 holley tbi on. It will run very rich and act like its got a huge vacuum leak when I first fire it up when cold. It will gradually get better until it goes away after about 3 min. Some times at 5000 rpm the motor will break up really bad. Other times the idle control motor will keep the rpm's at 1500 instead of the normal 550. The truck is fastest when the fuel pressure is at 8 psi. I tried running it around 12-15 like holley said but it just runs too rich and is very sluggish even after a couple of weeks. With the pressure set at 8 psi it doesnt pull any harder than it did before i put it on. All the sensors checked out ok on the scanner. Is it possible the computer isnt adjusting to the increase in air flow. I know that holley says its tbi is for 87-89 trucks but i wouldnt think it shouldnt matter. I dont know what to do. please help!

Mitch

 

I have the EXACT SAME problem with mine. I was gonna call Holley this week, but I got home too late each day this week.

 

Do you have any other mods to the engine or is the new tbi it? Do you have cold air induction or ram air or is this thing just under the hood? Did holley recommend this size for the 350 or is it something you just wanted? Lastly whether holley did or did not recommed this tbi for this engine why did you go so huge on cfm's? Reason is I have heard a few things about air flow. Like with anything there is a balance. The balance here is getting enough flow, which you seem to have, compared to the quickness of the flow. Volume compared to speed. If you have a huge intake the air will not pass through it as fast compared to a smaller intake where the air has to speed up to pass through. I read an interesting article some time ago and they mentioned that Nascar runs a mid-upper 300 cfm airflow. In their situation the air enters the intake much faster than it would into a 670 cfm. It sounds like at your top end the engine does not get the speed side (air speed) of this balance, sure it might get alot of air but it has to work to get it into the intake the air is not there ready to shoot into the cylinder by itself.

 

If you haven't changed much just remove the injector pod and put the stock one back on. See if that fixes your issues and returns the car back to near stock feeling. Just work backwards until you find the problem.

 

The motor is completely stock except for headers, the edelbrock tbi intake, and the holley tbi. Being that its a 350, i wouldnt think 670 cfm would be too much for the motor. Plus holley says it should work fine on stock 350 engines. Putting the stock tbi unit back on was actually my next step so I can see if the holley tbi is causeing the problem or if there is a problem somewere else. Id have already done that but I left my old one at advance and they sent it back as a core . So I gotta find another one now.

I shouldnt need a custom chip now should I? I know holley clams that the computer will adjust to the mods. Could I take a chip out of a ss 454 truck and put it in mine since the tbi flow the same to make mine run better? I tried emailing holley and they just tell me to make sure everything is pluged in right.

 

no a 454 chip won't work, it sounds like they lied. The ecm doesn't compensate very well to mods, it isn't a MAF system!
Get a stock TB and see if your problems go away. Then just swap the injector pod to see if it was just the injectors. Then check fuel pressure, TPS voltage, the normal stuff.