Idle issues on TBI Truck......

[Boaterbum]

Well, where do I start! I decided to try this out here, since I can;'t figure out the problem! I Have a 91' Chevy K2500, had a stock 350 in her, killed that at 150,000, (read: BIG HOLE and a 3 piece crank!)
Anyway, i found a 355ci, block, CHEAP, had to take it out to .060" though to clean up the scoring, went through the entire engine, ground crank, new pistons, rings, ALL bearings, Comp Cam, ect ect ect.. I have the stock heads on it for now, mainly because I wanted to be able to use the belt and accesories setup with the engine, though I did clean up the heads a bit, and put in tighter springs and new rockers and pushrods. The pistons are around 9.6-1, Cam is the Comp Cams 270 grind, there truck cam.
I have the stock throttle body on it now, stock intake, as well as stock ignition.
I think the distrubitor is going, or at leats week, so I want to go to an MSD ignition, BUT, not sure to change to a Carb motor, and replace the intake, ignition, carb, or just stick with the computer and grab the plug n play model from MSD.
The reason I thought about dumping the throttle body and puter', is because when the engine warms up, gets to temp (195ish), the idle is sporatic to say the least. It will try to idle down, then it will seem to want to drop off, the computer will compensate, and raise it to like 2000, then drop to 1000, and get worse and worse.. WON'T IDLE RIGHT. All I have to do is give a SLIGHT tap on the pedal, just enough to make it move the throttle cable, and it will be fine for a few seconds... I also have a K&N filter on a Velocity stack on the throttle body...
I am not sure what else to include here for info, any ideas??? Vacuum?? Throttle Body need work??? Throttle position sensor?? I don't know, anyone have any ideas??? Also, when the engine warms up, there is a TERRIBLE flat spot at like 2000-2300 RPM's.....
HELP! Thanks everyone!

[Boaterbum]

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[Boaterbum]

ALSO, I have a geared timing set, they say it will mess with the 'knock sensor', what would it do as for the engine running? Can I just unplug the sensor?? Emisions ARE NOT AN ISSUE, SHHHHHHH.....
also, I run Headman Headders, 2 and a half inch stainless exhaust to 2 chamber Flowmasters.

[Capt.Insane-o]

It won't hold a steady enough vacuum at idle for the computer to work properly. Try one of their Compu Cams, the computer friendly ones, and yes a gear drive does mess with the knock sensor, I assume you installed the O2 senson back in the proper place?

[Boaterbum]

I am looking for a block for the next engine, anyone in the area have a small block Chevy, 350, that they wanna part with?? Anything from a bare block, to, whatever ya have... Must be a 4 bolt main though... Thanks, Tony........

[Boaterbum]

hey, so, you say it would be the Cam?? Do they make a comparable one for the torque in that CompuCam?? I did put a new o2 sensor, around the same place as the origional, BUT, it would only be sensing one side of the engine, as the stock was after the Y pipe.... What effect does that knock sensor have on the engine? I aimagine it is going to retard the engine to get rid of what it thinks is a knock? Thanks for the input.......:D

[CDave]

I agree with the Capt. That is too big of a cam for stock throttle body and heads.

What kind of exhaust do you have?

The MSD is a good investment as long as you open up the plug gap. I run my plugs at .055 with a MSD 6/MSD coil and MSD 8.5 wires.

[Capt.Insane-o]

Put a Performer RPM and a good carb on it. you will be happy with the power you will pick up.

[Rickracer]

...cept for one thing, I'd go Holley instead of Edelbrock on the carb. A Performer or Performer RPM would be just the manifold though. :cool:

Edit: I just re-read the Cap'ns post and I see he didn't specify a Performer carb, just a good one. ;)

[1BadAction]

Originally posted by Capt.Insane-o
Put a Performer RPM and a good carb on it. you will be happy with the power you will pick up.

yes 100% tbi is junk. i hate it. its like the performance of a sorry efi and the sorry gas mileage of a poorly tuned carb. it is the worst of both worlds, imo the tbi setup isn't worth the steel its made out of. i replaced the 89 4.3 blazers tbi with a 450 cfm holley, i picked up 5 mpg up from about 13 avg. i didnt have a dyno but the motor was noticeably stronger.

i have had 3 tbi trucks, 2 of them have did the same thing you describe the 3rd one has held out until 310,000 miles, now its starting. the problem is with the injector, its not dirty, just getting worn out, it happens. the 2nd one i replaced the injectors, and cured it, and the 1st i changed to carburation. you will never get the stock computer to work, and you cant buy a aftermarket chip that will be for YOUR truck. to fix the injectors, get a custom chip, computer time, its not worth it.

[Scream And Fly]

Badstream, remember the dude who pulled your boat out of the water at Alva?

Greg

[1BadAction]

Originally posted by Scream And Fly
Badstream, remember the dude who pulled your boat out of the water at Alva?

Greg

yeah sure y?

[Scream And Fly]

Do you know who that was?

[1BadAction]

havent the foggiest

[Scream And Fly]

It was me. LOL!

Greg:)

[1BadAction]

i thought that pic that t-rex posted of you looked familiar. nobody intoduced us so i didnt know that it was you. heck, half the time i meet someone and then i forget. have you been going out to alva lately?

[Scream And Fly]

No - haven't had the chance. Been so busy here with S&F stuff. I need to get new camera equipment, so that should be fun. I don't want to hijack this thread any longer.. Sorry guys, didn't mean to. Back to truck talk.

Let me know when people are going there again!

Greg

[Boaterbum]

Thanks alot guys, I agree on the POS tbi setup, it is nothing but a poor stab at efi, my opinion of it is a cheap electric carb! Less the float bowl. I am going to order up a performer Intake, a Holly Truck Avenger Carb, and an old style MSD Distributer then, sounds like the way to go.....
Do any of you know what triggers the e;lectric fuel pump on my setup? Just ignition on? I will install a regulator for the carb, but, what other complications can I expect when eliminating the computer???
Thanks alot guys...........
~Tony~:D

[Capt.Insane-o]

It's been awhile, but someone makes a new gas tank insert that replaces the stock pick up/ fuel pump deal so a regular fuel pump can be used. Maybe Rick knows. That thing is going to run so much better...........:cool:

[Rickracer]

The TBI is only a 13~15 PSI system anyway. :cool:

[Pro350Hydro]

I have had the same idle problem with my tbi.

92 350 k1500
265,000 miles
rebuilt at 183,000
I have a cam that is computer friendly and works good, it is a comp cam, but cant remember the numbers off hand

BEFORE you tear off all the tbi stuff, check your EGR valve, i fought this problem for a long time. I replaced the injectors, throttle position sensor, idle solenoid, wires, i was just throwing parts at the thing, and it ended up being the egr valve. This was like 2-3 years ago. This last spring my brother in-laws truck an 88 350 k2500 started doing the same thing, it was the EGR valve also.

There are a couple different models, so you will need to get the numbers off of yours to get a new one. Also check the small hose that plugs into it, and runs over to the other small black box. Make sure it's not cracked or something. You can also unhook that small hose, and plug the egr valve itself, and the hose and drive it like that. If it runs better that is for sure your problem, however driving it like this will make the check engine, or service engine light come on. Don't worry about it, just buy a new egr valve for fifty bucks and be done with it.

Sorry for the long post, hope this helps with your troubles.

Keep me posted on your findings.

Mike
R-15

[Boaterbum]

I will check into that as well, sounds a helluva lot easier, but, I do want to gain more power, and think the carb/intake would do me some good eventually anyway, since the mota' is FARRRRRR from a stocker! But, yes, I am definately going to check that out with the EGR in the morning.... Thanks for all the input from everyone, still say this has got to be the best damn site out here! Anyway, thanks again everyone, always open to new ideas, so.......
I know the tbi fuel system is a relitively low pressure system, but, what controls the pump? Is that just ignition on activated? Thats not anything inj the computer, is it?
Thanks,
~Tony~

[Pro350Hydro]

Tony, I think the fuel pump is key on activated. Also, that egr valve problem will not show up on any scanners. That is why I had a hard time finding my problem originally.

Mike

[Rickracer]

But if you know what you are looking for, it isn't hard to diagnose. The fuel pump works two ways: 1st it cycles the pump on for about two seconds, (the computer does that), then once you have oil pressure, the ignition controls it from there, through the oil pressure switch. So either make sure you keep the same setup, or wire around the switch. I would keep the switch system intact though. It's a good safety feature. :cool:

[Boaterbum]

Damn GM, why'd they have to go anddo that with the Fuel pump? I was hoping I could rip all that crap out, pop in a regulator, and have the pump come on with the ignition! Anyway, I am going to have to go through the electrical system and see what I can deactivate and leave alone... i ideally wanted to eliminate the whole computer, and go to an old styly setup, but, not sure what that will do to the charging system and other stuff.... ARGHHHH....
gonna look into that EGR valve in the morn, will let ya know what i find.......
Tony.....

[fastboat]

Just a word of caution that may, or may not, apply. I have an '82 Corvette that I converted to carb and removed the computer. I didn't know that the computer also controlled something in the trans., and the first time I took it on the interstate, I burned the trans. up. Expensive lesson.:(

[Boaterbum]

I hear what your saying there Fasboat, but I have a manual trans in her, so, no torgue converter to worry about being computer controlled or shift points ect ect ect......
The only thing I could possibly see being a problem with that stuff might be the speedometer, BUT, I ca just eliminate that and go GPS or an aftermarket unit..........
Later man, Tony.......

[Rickracer]

The 2 second deal is for FI. If it has no pressure, it gets no fuel. The carb should always have some fuel in da bowl. Just make sure you pay attention to keeping the same oil pressure switch wiring and it will be just fine. :cool: