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Help...fuel injection TBI

Brett

Brett

Meat-Hippy
Location
Salt Lake City Utah
Okay, as some of you may have seen, I posted some questions before. I'll start with the basics.

73 Chevy 350 block and heads
88 Intake manifold, TBI unit, distributor and computer from a 305
Painless Wiring harness
All new sensors (TPS, IAC, Temp, oil switch, knock sensor, MAP, O2)
Ignition module, cap and rotor are new

The only thing that isn't new is the Electronic Spark Control unit and we tried another one and it still does the same thing.

Problem is that it doesn't want to idle properly. It will sit there and surge back and forth between 500 and 1000 RPM's. We did find one vacuum leak and plugged that up and seemed to solve the problem but now it's doing it again and I can't figure out why. If we unplug the MAP sensor, it'll idle along just fine, but you can't drive it since it loads up and bogs out. We're pretty much out of ideas on what else to try. We've been told that the computer would compensate for the displacement difference, but could this be the very problem??? This was supposed to have been out and running last weekend!

Please, oh please, great gods of RME, tell us what is wrong!
 
Last edited:
Milner

Milner

formerly "rckcrlr"
Location
Hiding behind a camera
Brett said:
Okay, as some of you may have seen, I posted some questions before. I'll start with the basics.

73 Chevy 350 block and heads
88 Intake manifold, TBI unit, distributor and computer from a 305
Painless Wiring harness
All new sensors (TPS, IAC, Temp, oil switch, knock sensor, MAP, O2)
Ignition module, cap and rotor are new

The only thing that isn't new is the Electronic Spark Control unit and we tried another one and it still does the same thing.

Problem is that it doesn't want to idle properly. It will sit there and surge back and forth between 500 and 1000 RPM's. We did find one vacuum leak and plugged that up and seemed to solve the problem but now it's doing it again and I can't figure out why. If we unplug the MAP sensor, it'll idle along just fine, but you can't drive it since it loads up and bogs out. We're pretty much out of ideas on what else to try. We've been told that the computer would compensate for the displacement difference, but could this be the very problem??? This was supposed to have been out and running last weekend!

Please, oh please, great gods of RME, tell us what is wrong!
Click to expand...

Good idle when you unplug the map makes me think there is still a vacum leak somewhere....
305-350 won't effect anything....
 
Caleb

Caleb

Well-Known Member
Location
Riverton
Sounds like my 4.3L...same thing, Dennis at Mepco ended up finding the problem as being a bad fuel regulator.
 
Caleb

Caleb

Well-Known Member
Location
Riverton
mbryson said:
Sounds like a vacuum leak to me as well. (but then Caleb chimes in with the fuel regulator....plausible, IMHO)
Click to expand...
I was skeptical as well, I had a new regulator on it and they replaced it with a used one. It fixed my problem. I was sure it was a vacuum problem.
 
7

78mitsu

Registered User
On a GM, you should be able to unplug the sensors one at a time, the ecu should fallback to a pre-defined fuel management table, I'd try the IAC, hold the throttle open just a hair. also could be malfunctioning knock sensor, it can cause the engine to flutter back and fourth at idle.
 
Brett

Brett

Meat-Hippy
Location
Salt Lake City Utah
78mitsu said:
On a GM, you should be able to unplug the sensors one at a time, the ecu should fallback to a pre-defined fuel management table, I'd try the IAC, hold the throttle open just a hair. also could be malfunctioning knock sensor, it can cause the engine to flutter back and fourth at idle.
Click to expand...

Hmm....I'll have to check the knock sensor. I remember I was trying to unhook it....I wonder if I didn't put it back on right.......:eek:
 
sbr

sbr

Registered User
Have you tried unhooking the egr valve. My brothers had some problems at low rpm and unhooking the egr made a world of difference
 
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