TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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-Saving up money to buy an EBL right now, should be into tuning my cam, heads, intake LO3 by the end of the summer.
My concern is that my engine is running like crap right now due to the lack of tuning (suprise, suprise). I don't even want to drive it on the road cos at higher RPM's the engine starts coughing and is really bogging down. I thought it was due to improper ignition timing so i took it to my mechanic to get it running better. He looked at it, but left the timing where I had it (advanced to 2) saying that it was all due to fueling and computer probs. He said tune it!!!
I know it's gonna be at least another month til I get the EBL and figuring in the learning curve of tuning, a long while to get things working like they should. I wanna hit some local shows and cruise-ins in the next couple months so I really want to at least make it streetable without the EBL. Any tips to cure the coughing-bogging down issues??
I was thinking about moding the stock FPR to bump up the Fuel Pressure a little bit. Would this help any?? Any other tips would be greatly appreciated! I wanna drive my L03 this summer!!!!!!!!!!
Not seeing any modifications and assuming none, I would start with a complete tune-up (replace all from rotor to plugs), pull the dizzy and re-align it with TDC in case it has jumped a tooth and check your fuel pressure at idle -> WOT.
Make sure when you check the timing with the EST wire disconnected and that you plug it back in after.
Use some starting fluid to check for vacuum leaks since that has a big impact on fueling.
Honestly, getting ebl and being able to use WUD and logging would take much of the guess work out.
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Not seeing any modifications and assuming none, I would start with a complete tune-up (replace all from rotor to plugs), pull the dizzy and re-align it with TDC in case it has jumped a tooth and check your fuel pressure at idle -> WOT.
Make sure when you check the timing with the EST wire disconnected and that you plug it back in after.
Use some starting fluid top check for vacuum leaks since that has a big impact on fueling.
Honestly, getting ebl and being able to use WUD and logging would take much of the guess work out.
-Distributer/rotor:Check
-Plugs: Check
-Set timing w/ disconnected EST: Check
-My Fuel Pressure at idle is 11 psi and dives down to 9-8 PSI at WOT
-I know my vacuum is messed up b/c my mechanic replaced my rear drum brakes while he was looking at the timing and they (brakes) still don't work very well at an idle-low speeds. He said it was a vacuum issue and told me to get an electric vaccum pump. I didn't know that the vacuum messed up the fueling too so maybe that's what's going on right now. Maybe I should get the pump before the EBL?
Last edited by Shakermaker05; 06-09-2009 at 09:55 PM.
Yes EBL will help you discover many things, you can also properly set it up for VAFPR.
Stock cam and vacuum issue?
As you go WOT FP should increase, are you sure you have a VAFPR? If not FP should stay steady.
My mechanic said my Vacuum problem was from the .480-.487 lift comp cam I put in, but the strange thing is, is that it worked fine 2 summers ago when I installed it. The car was streetable and ran very strong with the upgrade. It wasn't until last summer when I put the World Heads on 'til all this stuff went wrong. Upon initial start-up after the install I had about 10% of my normal braking power and I have not been able to fix the bogging coughing problem at higher rpms.
As for the fuel pressure: I don't have a fpr or a modded stock fpr. I just bought a summit fp gauge and installed it into the line right by the power steering pump and as mentioned above my fp is reading around 11 psi and is definitely dropping 2-3 psi upon reving the car up which is when it starts coughing. Sounds like it's a good thing I have a new Walbro 255 lph waiting to be installed. I was just debating whether or not to drop the tank or cut the access panel.
I'm running a LT-4 hotcam with .525/.525 lift and don't need a vacuum pump. The drop in FP indicates the pump can't keep up. It is common for the little piece of rubber hose in the tank to split causing the drop. Happened to me.
I've read that going to a 255 pump mandates a larger return line. Do some homework on that. I'm running a 190 and it is feeding my set-up well.
Drop the tank. I have done both. Since I have dropped my tank quite a few times now, I can get the whole job done single handed in a few hours. Just make sure the tank is empty. If not, jumper the fuel pump while the feed line is disconnected by the intake. I ran a air compressor hose from that to my girlfriends gas tank. When the tank is down, you could cut the access panel, but it requires also making mods to the hard lines that come out of the top of the tank, cause if you leave them the stock length there is not an easy way to pull the pump out without bending those lines. Remember to take the bolt out that holds the brake line T to the diff and the one that hold it to the frame. I forgot once and broke the line.
Put a vacuum gauge on it. It sounds like you have a leak. All fueling is done by referencing the VE table which is RPM vs MAP (Map is the inverse of vacuum). At a constant crusing rpm you should be around 15 and pegged at 20 during decel.
I've read that going to a 255 pump mandates a larger return line. Do some homework on that. I'm running a 190 and it is feeding my set-up well.
I've heard it both ways. I've had guys tell me to put in the different line and others have said not to worry about it. Kinda just scratching my head on that one right now too lol. It's looking more and more like I'll drop the tank to do the install. I will take your advise and look for vacuum leaks. It would be great if I could get around the vacuum pump as it's around the $200 mark at Summit : (
Last edited by Shakermaker05; 06-10-2009 at 12:50 PM.
My mechanic said my Vacuum problem was from the .480-.487 lift comp cam I put in, but the strange thing is, is that it worked fine 2 summers ago when I installed it. The car was streetable and ran very strong with the upgrade. It wasn't until last summer when I put the World Heads on 'til all this stuff went wrong. Upon initial start-up after the install I had about 10% of my normal braking power and I have not been able to fix the bogging coughing problem at higher rpms.
As for the fuel pressure: I don't have a fpr or a modded stock fpr. I just bought a summit fp gauge and installed it into the line right by the power steering pump and as mentioned above my fp is reading around 11 psi and is definitely dropping 2-3 psi upon reving the car up which is when it starts coughing. Sounds like it's a good thing I have a new Walbro 255 lph waiting to be installed. I was just debating whether or not to drop the tank or cut the access panel.
I missed your mods. Yea definally something wrong if you have only 11psi and it drops under load. I have no idea how it works without a FPR. Sorry I dident get it that you were debating about dropping the tank or not.
Last edited by thomas1976; 06-10-2009 at 06:29 PM.
I missed your mods. Yea definally something wrong if you have only 11psi and it drops under load. I have no idea how it works without a FPR. Sorry I dident get it that you were debating about dropping the tank or not.
That's OK man. I figured it was abnormal for the FP to drop under load, but I'm glad I got it verified on here. I bought the Walbro pump a couple months ago, but I wanted to do some research on the access panel vs tank drop to install it. I'm going to try and get it installed in the next coulpe weeks and try to figure out the vacuum issue. As stated above, I will keep you all posted as to the outcome of this situation.
I bought the Walbro pump a couple months ago, but I wanted to do some research on the access panel vs tank drop to install it. I'm going to try and get it installed in the next coulpe weeks and try to figure out the vacuum issue. As stated above, I will keep you all posted as to the outcome of this situation.
