tbi frustration

[lewis]

I have put a tbi system on an 85 350 that ran good before I put it on and I can't get it to not run lean. It idles fine and then when a load is put on it it will bog down and throw flames out of the throttle body. I got the tbi system off of an 89 and bought a painless harness. I used a throttle plate to connect it to the intake manifold. I have switched out every sensor, computer, and even put in a 454 chip to dump more fuel in but still to lean. I am running a holley fuel pump, 15 psi with a half inch hose feeding it. I have run out of ideas on what it may be and wonder if anyone has used one of these throttle plates before cause I have done the switch over before but used the aluminum intake that goes with the tbi and had no problems.

 

[78mitsu]

any chance you have your distributor at 180* out or your timing set funny, That's where I would start. also, any changes to the motor other then adding a tbi (roller rockers etc?)

 

[dunatic67]

How did you set the timing? Did you unplug the computer (Brown wire?) and set the base timing at zero?

 

[mbryson]

any chance you have your distributor at 180* out or your timing set funny, That's where I would start. also, any changes to the motor other then adding a tbi (roller rockers etc?)

Have you had an engine run at 180* out?


I'd swap over to the TBI specific manifold if possible. See if that helps...... Probably cheaper than any of the sensors you've replaced.

 

[78mitsu]

Have you had an engine run at 180* out?


I'd swap over to the TBI specific manifold if possible. See if that helps...... Probably cheaper than any of the sensors you've replaced.

yes, most V8 engines will run (badly with the symptoms he is describing) at 180 out put the distributor in backwards. I've got 2 engines now that I got for a steal because someone changed the distro and put it in backwards, couldn't figure out why. Easy to check, put your timing light on #1 and look to see if you see a timing mark - or bring the engine to top-dead-center and pull the cap and see if it's pointing at the #1 plug-wire. Eliminate that. Cracked cap can behave the same way, but I figured he'd already replaced it.

 

[mbryson]

yes, most V8 engines will run (badly with the symptoms he is describing) at 180 out put the distributor in backwards. I've got 2 engines now that I got for a steal because someone changed the distro and put it in backwards, couldn't figure out why. Easy to check, put your timing light on #1 and look to see if you see a timing mark - or bring the engine to top-dead-center and pull the cap and see if it's pointing at the #1 plug-wire. Eliminate that. Cracked cap can behave the same way, but I figured he'd already replaced it.

Hmmmm..... I've never got one to actually 'run' if it was 180* out. It just acted like it 'would', but would never fire. (and admittedly, I've not swapped a lot of TBI small block distributors out. A few HEI units on carbed engines, though.)

 

[78mitsu]

Hmmmm..... I've never got one to actually 'run' if it was 180* out. It just acted like it 'would', but would never fire. (and admittedly, I've not swapped a lot of TBI small block distributors out. A few HEI units on carbed engines, though.)

little more timing and it'll stay running.

 

[dunatic67]

bring the engine to top-dead-center and pull the cap and see if it's pointing at the #1 plug-wire. [/QUOTE]
When the engine is at top dead center it needs to be on compression, not top deae exhaust to check the distributor. pull the plug and put a finger in the hole to check that it is on compression.

 

[lewis]

set timing with brown wire unplugged to 0 degrees. I installed distributor with number one piston at tdc on the compression stroke. Has a brand new cap and rotor as well as plugs and wires. It runs really good at idle and when its throttled up its just when it has a load put on it by putting it in gear is when it takes a dump.

 

[mbryson]

set timing with brown wire unplugged to 0 degrees. I installed distributor with number one piston at tdc on the compression stroke. Has a brand new cap and rotor as well as plugs and wires. It runs really good at idle and when its throttled up its just when it has a load put on it by putting it in gear is when it takes a dump.

How do your plugs look? black, brown or white?

 

[Crinco]

This motor has a O2 sensor right? Unplug that (all the O2's) and run it and see if it runs better. It should stay in open loop and run richer. If that doesn't help I think I would say it isa timing problem. Do you have a laptop? There are several programs on the net that you can use to diagnose "some" TBI's out there with a laptop, software and a cable that goes to the ECM. I would save that as a last resort though.
Are the injectors plugged up so they can't put enough fuel into the motor? Try to look at the spray pattern, but don't let it back fire on you. Are both injectors working?

 

[wr250]

set timing with brown wire unplugged to 0 degrees. I installed distributor with number one piston at tdc on the compression stroke. Has a brand new cap and rotor as well as plugs and wires. It runs really good at idle and when its throttled up its just when it has a load put on it by putting it in gear is when it takes a dump.

have a CEL hooked up ?
codes?
put in a new fuel filter? uhook and check for volume, as you already did pressure

bad fuel? sniff test

vacuum leaks (including intake manifold to head) ? use carb/brake cleaner to find, if idle change when a part is sprayed, you have found a problem

both injectors firing? unplug & ground coil wire, or unhook distributor plug(s), so there is no spark at all watch fuel injectors as someone cranks it. should be a fine mist of good volume

what is the actual ignition timing? both with the wire hooked up/unhooked

firing order wrong on 2 or more cylinders ?

lean conditions are caused by:
to much air
-bad o2 sensors (misreading as rich and cutting fuel)
-vacuum leaks
-manifold leaks
-computer/sensor problems

not enough fuel
-bad fuel pump (not enough pressure/volume)
-clogged fuel filter
-swollen/leaky rubber fuel lines
-(partially) plugged fuel injector(s)
-computer/sensor problems

flames out the TB indicate :
ignition timing timing problems -firing order(1-8-4-3-6-5-7-2), advance set wrong ,distributor off a tooth, etc
valve timing problems (unlikely if you didnt go into the motor)

at TDC on compression, the rotor should be pointed at the #1 cylinder.
on the newer style "flat" caps with the plug wires coming off the side of the cap (vortec motors i believe, could be wrong though), the procedure in the manual must be followed to the letter (and you need a scantool). otherwise the motor will run as you describe. older HEI style caps do not have this problem.

 

[drylok]

Doesn't TBI need to have about 45 psi of fuel pressure???

 

[mbryson]

Doesn't TBI need to have about 45 psi of fuel pressure???

I think it's closer to 12-15 psi.....

 

[Milner]

Doesn't TBI need to have about 45 psi of fuel pressure???

Tune port or SEFI need that much, but like MBryson said, not throttle body...

You didn't mention a return line. Do you have one? what size?
Also, look for mechanical interference....When in gear is the drivetrain torquing? Are wires being stretched, is something making contact some where? Spark issue? Have you checked voltage at the computer and coil in gear?

And what should be my sig....Have you checked ALL the grounds?

 

[lewis]

have a CEL hooked up ?
codes?
put in a new fuel filter? uhook and check for volume, as you already did pressure

new filter, no codes

bad fuel? sniff test

new gas
vacuum leaks (including intake manifold to head) ? use carb/brake cleaner to find, if idle change when a part is sprayed, you have found a problem [/QUOTE] vacuum leaks tested no leaks

both injectors firing? unplug & ground coil wire, or unhook distributor plug(s), so there is no spark at all watch fuel injectors as someone cranks it. should be a fine mist of good volume

replaced injector both flowing well

what is the actual ignition timing? both with the wire hooked up/unhooked

0 wire unplugged advances with throttle up like it should

firing order wrong on 2 or more cylinders ?

firing order perfect

lean conditions are caused by:
to much air
-bad o2 sensors (misreading as rich and cutting fuel)
-vacuum leaks
-manifold leaks
-computer/sensor problems

no computer or sensor problems(have lots of spares that I know work well) , no manifold leaks

not enough fuel
-bad fuel pump (not enough pressure/volume)
-clogged fuel filter
-swollen/leaky rubber fuel lines
-(partially) plugged fuel injector(s)
-computer/sensor problems

using rubber fuel lines, blue, I was told they are stronger and don't swell

flames out the TB indicate :
ignition timing timing problems -firing order(1-8-4-3-6-5-7-2), advance set wrong ,distributor off a tooth, etc
valve timing problems (unlikely if you didnt go into the motor)

also caused by running lean( if you don't believe me I can show you)

at TDC on compression, the rotor should be pointed at the #1 cylinder.
on the newer style "flat" caps with the plug wires coming off the side of the cap (vortec motors i believe, could be wrong though), the procedure in the manual must be followed to the letter (and you need a scantool). otherwise the motor will run as you describe. older HEI style caps do not have this problem.

Timimg not an issue willing to stick out my neck on it.

 

[lewis]

You didn't mention a return line. Do you have one? what size?

yes have one 3/8".

Also, look for mechanical interference....When in gear is the drivetrain torquing? Are wires being stretched, is something making contact some where? Spark issue? Have you checked voltage at the computer and coil in gear?

And what should be my sig....Have you checked ALL the grounds?

drivetrain torquing but not pulling any wires. Haven't checked voltage at computer when in gear but don't see how that should make the voltage drop. all grounds are good.

 

[lewis]

another part of the story is that it runs just fine when the motor is cold. tons of power and drives like a champ. When it gets above 120 degrees or so it sucks.And when i tried to put the 454 chip in it won't even run when its cold because it floods it out, but then when its warm it will still run lean.

 

[Jinx]

I have put a tbi system on an 85 350 that ran good before I put it on and I can't get it to not run lean. It idles fine and then when a load is put on it it will bog down and throw flames out of the throttle body. I got the tbi system off of an 89 and bought a painless harness. I used a throttle plate to connect it to the intake manifold. I have switched out every sensor, computer, and even put in a 454 chip to dump more fuel in but still to lean. I am running a holley fuel pump, 15 psi with a half inch hose feeding it. I have run out of ideas on what it may be and wonder if anyone has used one of these throttle plates before cause I have done the switch over before but used the aluminum intake that goes with the tbi and had no problems.

This might be a little bit off but is there a pinch in the return line? I have seen where the return line not allowing enough flow therefore causing too much pressure and hydro locking the injectors... TPI system though...

Something that hasn't been mentioned...

 

[dunatic67]

Hey Lewis, it sounds like you have been pretty careful. I have a friend who has the laptop software to run the computer and see what it is really happening. He can burn chips as well. He is a mechanic in American Fork. PM me if you want his info.