TBI help needed
 

I need help figuring out my tbi on a 1990 Chevy 454. It is pouring fuel thru and flooding the engine. If you disconnect one of the injectors it will run but not great. I have new injectors and a new regulator in it. When we first started it was running great. It started the flooding after it was drove for about 2 miles.

Any help or suggestions would be greatly appreciated.

Check your coolant temperature sensor. Usually when they fail the PCM thinks the motor is stone cold and dumps way too much fuel in. Also just because the temp indicator on the dash looks okay does not mean the one for the PCM is okay they are usually two different units one for the gage is on the head and the one for the PCM is on the manifold.

Bill Edgeworth
6471 J/SA Firebird

This is going to sound stone age but while the engine is running tap on the top of the bad injector with a screwdriver handle, I had this same thing happen to me with my 88 when i rebuilt the T.B.I, what happens is that the pintle valve sticks in the injector and it floods.


Terry
Carp'e diem

I would definately say coolant temp sensor located on front of intake manifold. Run into this alot up here in cold cold canada!

Thanks guy's I tried the tapping trick with no luck. I will be trying the temp sensor and a new O2 sensor tonight. Any chance some one knows what resistor I can jump across the connection for the coolant temp to make it think it is fine.

Also is there any chance that a bad throttle position sensor could cause a problem like this. I was going to try a new one but nobody around here seems to stock them.

Thanks John

Check your running fuel pressure, if it's low, it will dump fuel.

If the wiring harnesses to each injector get crossed, it will run poorly.

"Despite the high cost of living, it remains popular"
Dave Cook
C375

Almost all of the sensors are 0.0 to 5.0 volts. The O2 voltage is 0.0 to about 0.99.

The TPS voltage should be around 0.46 at idle, and around 4.6 at WOT.

The O2 sensor should switch back and forth across 0.500 volts, usually varying from around 0.300 to around 0.700.

At idle, the MAP sensor should be either about .50 volts or 4.5 volts, I cannot remember whether that particular model read high voltage with high vacuum or low voltage with high vacuum. It should swap either from about .50 to about 4.5 or from 4.5 to .50 when you take the vacuum hose off of it.

The fuel pressure should be around 24-25 pounds.

I can tell you that coolant temp sensor failures are very common, and if it is dead, it defaults to -40 degrees, which commands a full rich signal. The coolant temp sensor works like the MAP sensor in that it reads from .5 volts to about 4.5+ volts. You can check it the same way, when it's cold, it should read opposite of warmed up.

Make sure it is full of coolant, and if it does not have a "chip" in it that the thermostat is rated at 195 degrees.

In order of common failure, the coolant temp sensor is first, the O2 sensor is a close second, the MAP sensor is third, and the TPS is fourth.

Ground issues are VERY common, especially when work has been done, particularly engine swaps or replacements. ALL of the grounds MUST be perfect, they need to be clean and tight, with no paint or rust on the ground wire or stud. Also check for pinched wires.

Finally, make certain that you use genuine GM parts when servicing the computer, fuel and ignition systems. The cheap aftermarket stuff is nothing but trouble. Yeah, it's more expensive, but buy your parts from the dealer. You can usually use MSD stuff in the ignition, and good wires like you'd use on your race car. PREMIUM aftermarket fuel system parts, like MSD or Holley, or maybe Accel, are okay, if you're looking for a little power.

P.S. If you've put headers on it, make sure the O2 sensor is not too far from the engine. If it is, either move it close, or convert to a heated O2 sensor.

Alan Roehrich


Bring "AA" classes to NHRA Stock Eliminator!

Thanks every one. The temp sender was the guilty culprit.