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TBI Question

S

Shagnaz

1/2 ton status
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Jul 19, 2002
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Location
South Carolina, North Charleston
Just installed a 355 in my 90 K5. I put a computer cam (RV cam),Edlebrock performer(dual plane) intake, and everything else is basicly...basic. Nothing radical. Well, I get everything in, set the timing and it fires up. But I am only getting 15 in. lbs. of vac. I need 18. I play with the timing some, but end up too advanced. Another problem...won't idle. UP and DOWN.
Well, we thought it was the IAC. Well, we put a Holley 670 on it to be able to get an adjustable TPS also. Runs better, but NOW it breaks up at @ 2500 during normal driving, but WOT is fine.

Anyone have this problem or know why it would break up?

Anything will help. I am at a dead end.

One more thing. I set timing at 4 deg TDC. It calls for 0, but with that cam, figured I could advance base timing 4 deg.

Thanks...if any other info is needed, I can provide.
 
are you using the edelbrock tbi performer or a carb style dual plane performer? Are you throwing any codes w/ the ses light?
 
It's the carb dual plane w/ TBI adapter. I am throwing codes, but they are from the engine idling to low and no EGR. I try to idle the engine up, but seems like it gets bogged down. The idle is up and down? The idle air is working, but the comp can't seem to keep it at a constant rpm. I checked for vac. leaks, but none were found.
The TPS was set .5v +.
Anything?
 
i would drop the timing back to zero and check for vacuum leaks.Also was the timing chain set up pre-advanced or strait up?
 
I have heard bad things about using the adapter plates when using a tbi on a non-tbi intake. I would switch out the dual plane w/ a tbi intake/egr valve set up. Before you do that double check the specs on your cam, especially the lobe seperation, it needs to be at least 112 to get enough vaccuum, for the tbi computer to be happy. So if you have not enough lobe seperation and the adapter plate you probably need a custom chip. Also checkout www.thirdgen.org
thers lots of good tbi info there.
 
As far as I'm aware the timing must be at 0. The truck needs to be driven at a steadt speed 30/35mph I think for the IAC to 'find' itself and set up a base reading. Good luck. /forums/images/graemlins/thumb.gif
 
I set the timing chain straight up. It was a normal double roller chain.
I have the orginal style spark plugs in it right now for the 90 set up. The motor came out of a 84 Vette before I rebuilt it. I am going to change out the plugs to the 84 vette style, get a piston stop to find TDC(again), set the distrib, and then see where I am at.
The orginal set up that I had was a modified "fast burn" head intake (4 center bolt are vertical). I angled the center hole to work with the angled heads. Hope I am explaining everything clearly. I had 15 in lbs. of vac. I really didn't like that set up, so I went to the carb/adapter set up. Same vac. I am going to start from scratch with the timing, then move to the TPS. If that doesn't work...either go with a carb or replace the cam.
I am pretty much a dead end. I was even thinking of puting a vac. pump on the map to see if it would idle nicely. Just as a test.
The cam is just a computer cam. Either 112 or 114 duration.
Does anyone have a diagram of the Holley 670 vac. ports and what need to be used on what? I have the map on the back side of the TBI unit between the feed and return ports.

Thanks for all the help. Anything will help or at
least keep the mind thinking.

Thanks again
 
I assume you are using the stock computer out of your truck w/ a holley tbi. I would try a stock gm tbi w/ the stock computer and see what you get. I have to believe that your problem is with the mismatch of the holley tbi, the dual plane intake and the stock computer. Again you should either run the winaldl program to get the learn numbers to get a custom chip made or switch out the holley tbi / dual plane intake with a stock gm tbi and a stock or edelbrock tbi manifold. Your cam grind sounds computer friendly. One other thing is if you are running long tube headers and have the o2 sensor by the collector you will need to run a heated o2 sensor becuase the exhaust gas cools off too much by the time it reaches the sensor
 
I am going to try that heated O2. I did put it down at the collector. I also have a 160 deg stat.. The thirdgen site was saying that it wasn't a good thing to run a 160 b/c it will constantly run rich, which that is what it is doing at idle. So, I have a list of things to do and maybe this problem will be solved or I'll just slap a carb on it and be done with it.

Thanks /forums/images/graemlins/thumb.gif
 
Does it run this way when the engine is cold? I have a feeling it does. Does it also do it when it's hot or haven't you driven it yet? The O2 and thermostat have no bearing on anything if it does it when it's cold. You really need to scan the thing with winaldl to see what's going on.... BTW what are the codes it's setting?

Andy
 
You need to at least be running a 180 degree thermo. I have an RV cam in mine and I still had to end up putting a vac canister for my brakes to function correctly and it to idle better. /forums/images/graemlins/waytogo.gif
 
I don't know what codes it is setting and we are waiting for the adapter for the scanner.
Are you running TBI also with the RV cam. Did you run into the same problems. I haven't changed anything out yet, but will keep updates coming.
Did you ever put a vac gauge on you motor. What was the reading?

Thanks
 
One thing you should try is unplugging the IAC motor before you start the truck and see if the idle still goes all over. If it doesn't rev up and slow down you'll know the computer is controlling the speed and likely you'll need some programming or something else to make the ECM happy...

Andy
 
I have to agree here. Running a heated O2 with long tubes is NOT "required". In some instances perhaps, but I can say with certainty mine heats up fine, and I'm running long tubes.

I would certainly step back up to a 180* or 195* thermostat, it eliminates the chances for problems with the ECM, (which also really don't seem to be prevalent even with the 160* stat) and really doesn't net you enough gains to make it a worthwhile swap in the first place.
 
I have had the best luck with a 180 thermostat in my junk. I had problems with a 160 *overheating* my 454 but when I went to the 185 it's dead consistent.

Andy
 
This is a reply to everyone...
I went to move the truck into the garage yesterday and while it was cold, I tried to rev the motor alittle, but it was sputtering when I gave it gas. Don't know it it is b/c of the amount of fuel, or the plugs are just fouled out from running rich from the times before.
I am planning on working on it tonight and will post up anything that comes up.
Has anyone had these similar problems?

Thanks and keep the knowledge coming! /forums/images/graemlins/thumb.gif
 
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