tbi trouble

[brsampedro]

recently purchased a 91 k5 w/ 350 tbi, im losing hair trying to figure out my problem getting it running, the previous owner had replaced the distributer and coil along with fuel pump and filter, i had gotten it started but he never tightened or timed the dist. due to not having proper tools, so my next step is to get it timed and tightened, well like i siad had it running and now all of a sudden it wont get gas out of injectors. if i hot wire one gas sprays out with good pressure and obvious power to them. all harnesses are getting power (12v) when i test them with a light n such, i fiddled with the wiring and got it started again but then when i went out the next day to time and tighten the dist. i couldnt get it started , im wondering if i have a short somewhere, i can see the left injector harness is burnt and semi melted but still geting power also the coil harness that the wires go from coil to control module are spliced and connected with connectors , so work has been done in this area before?.. im wondering if im missing anything i want to replace the burnt out harness obviously but it was running with it burnt any info would help i know this has been posted before but ive tried everything and just dont wanna go out buying a bunch of parts and get no return, also fuses are all good and ive also checked for codes,just trying to give as much info as possible thanx for your replys

 

[Jessie James]

When you time it, remove the tan with black stripe EST wire from the distributor. You must do that otherwise the timing will be way off, and you probably won't be able to start the truck.

When you crank it (have someone help) does fuel flow from both injectors?

When it's off, but ignition is on, they should not drip or flow (leaking injectors).

Disconnect the electrical connectors to the injectors and then crank the engine. They should NOT flow ANY fuel. If they do, replace them.

Check the fuel pressure. It should be 9-13 PSI.

A grounded EST wire will cause this. (This is the same brown and black stripe wire that you remove when timing it.)

Is the engine flooded? This happened to me. Remove all the plugs, remove the coil wire to the distributor cap, and turn it over. Have a fire extinguisher nearby and do NOT have anyone standing near the engine compartment in case of fire (this happened to me!)

Of course, do you have spark?

How are those spark plugs? I just replaced the ones on my newest truck and they were DEAD and there were two different kinds - not even the right ones! Get Delco OEM plugs or NGK V power for best results.

Are the wires in the correct firing order? Never assume it's correct if it never ran. Verify each wire from the cap to each plug when it's a TDC.

Also, while you are in there, replace the termostat with a 190-195 degree jobber. The TBI does not work well with anything cooler, but some people don't know that and put a 160 degree unit in there.

The exhaust could be blocked. You could probably remove the cat from the Y-pipe if it's not welded, if it is then you may have to use a sawzall and cut it off. You can always use a wide exhaust clamp to put it back together.

Finally, you could have stuck or burned valves, sticking piston rings, a blown head gasket, stuck lifters, or a bad (flat) cam (this also happened to me - remove the valve covers and be sure all the valves are opening and closing fully).

Good luck. Once you get it running you will be very happy with the TBI. It is a very capable system!

 

[brsampedro]

got it running the other day so i timed and got distributer tightened, then when i got back from lunch went to start it ... nothing.

no fuel coming out of injectors at all when cranking, but i am getting fuel to tbi,( unhooked line from inlet and it poured out gas, while cranking and with key in on postion guessing cuz lines were priming)

motor gets spark, and when it gets running it runs great ,sounds great exhaust aint blocked

replaced the ecm cuz i got a codes 51 from ecm before now i dont get nothing but the 12 code from new one, im thinking its a sensor like map?

like i said before power is getting to everything and once every 10-15 trys it starts and runs great

im just lost and almost gonna give up and switch everything to a carb,
i have a 84 c10 stepside and its prob the best running vehicle ive ever owned

thanx for your help and input

 

[ccarley]

I'm going through trouble with the stock system; however I don't think I'd swap to a carb!

The TBI setup is pretty rock solid when working properly. My vote is to keep going through it to get it running right, then you'll be happy.

Good luck with the issues, sorry I can't be much more help right now.

Clay

 

[Jessie James]

no fuel coming out of injectors at all when cranking, but i am getting fuel to tbi,( unhooked line from inlet and it poured out gas, while cranking and with key in on postion guessing cuz lines were priming)

What happens when you apply 12v directly the the injectors with the ignition on? You should see fuel spraying out. If not, then you have a fuel pressure/delivery problem.

Have you checked the fuel pressure? With TBI it's not enough to just have fuel flowing, you must have 9 PSI to 13 PSI of fuel pressure. (Closer to 13, 9 is the bare minimum.) If you have low pressure, you may have a worn out fuel pump. If your pump pressure is ok, your fuel pressure regulator may be worn out, or your fuel filter may be blocked and need to be changed. (That's easy, and if you have never done it you probably should).

The fuel pressure regulator is a relatively easy fix. Remove the top portion of the TBI assembly (about 8 torx screws as I recall) and then the back portion has 3 larger torx screws. Remove those slowly as there is a big spring in there which you need to keep and put back together in the correct position. Remove the old regulator and put in your new one, cleaning things up first. Put the spring back in on the CORRECT SIDE and slowly put it back together so it seats properly.

If I were you, I would test the fuel pressure next. If the pressure from the line is good, replace the fuel pressure regulator. If it's low, the fuel filter and re-test. If that does not fix it, then it's your fuel pump.

replaced the ecm cuz i got a codes 51 from ecm before now i dont get nothing but the 12 code from new one, im thinking its a sensor like map?

Good move, code 51 is the ECM. Code 12 is just telling you it's in diagnostic mode, that's normal when you have the A & B terminals jumped.

Codes 31-34 and 61 etc are bad MAP sensor. Therefore, your MAP sensor is fine. DON'T REPLACE IT!

Don't start replacing perfectly good parts on a TBI system without proper testing, you will be wasting time, effort, and money!

im just lost and almost gonna give up and switch everything to a carb,
i have a 84 c10 stepside and its prob the best running vehicle ive ever owned

TBI is easy enough to work on, but you have to test things first. Once you get it working it will out-perform your carb vehicles every time.

Take a deep breath, we can help!

I suspect you have a fuel delivery problem, do those checks and let us know what you come up with.

 

[brsampedro]

i get a perfect cone when jumping the injectors with a hot wire, will get to the regulator n pressure probs this weekend but it seems to be fine, i think i may have staed also before i unhooked the inlet line and put a can under it for collection and when i turned motor it splurged fuel out

 

[Jessie James]

If you have the fuel spray cone when jumping the injectors, then you MIGHT have sufficient fuel pressure but you cannot be sure without testing it for real. To do that properly, you put the pressure tester after the fuel filter (under the truck on the passenger side inner frame rail). Of course, if the injectors are not getting a signal to open it doesn't matter.

What you need to do now is connect a 12v test light to the injector harnesses and see if they light up when you crank the engine. Do this next and report back.

The other thing you can check is if the EGR is stuck open, or if the EST wire (tan with black stripe to distributor) is grounded out.

 

[dessellier93]

having similar problems have gas good spray, good spark, just replaced wires,cap,rotor and it ran before it just wont start now i had just changed my intake gaskets put everything back together went to start and now it wont thought was flooded but fixed that any help? ideas?

 

[Jessie James]

Changing the cap and wires always makes me ask ... are you sure the timing order did not get messed up? Get it to TDC then pop the cap and be sure the rotor is pointed at the #1 wire.

 

[JPOutfitters]

Also, while you are in there, replace the termostat with a 190-195 degree jobber. The TBI does not work well with anything cooler, but some people don't know that and put a 160 degree unit in there.

What does a 160 degree Thermostat do to the TBI? I'm running one in mine and it doesn't seem to be hurting anything......but I don't want to give bad info either so I'd like to know.

 

[Jessie James]

What does a 160 degree Thermostat do to the TBI? I'm running one in mine and it doesn't seem to be hurting anything......but I don't want to give bad info either so I'd like to know.

It is giving you worse MPG and less power, and also will coat your O2 sensor with unburned fuel over time, and does the same to your catalytic converter (if you are running one), and can sometimes cause a fast idle because the ECM is trying to warm the engine up.

Basically, you are telling the computer that the engine is never warmed up and to operate like the choke is on, sending more fuel into the system for no good reason. The higher temps also help heat the intake manifold which in turn helps with fuel atomization which gives better performance. The ECM looks for a certain coolant temperature before it changes to closed loop mode. Open loop mode is when the engine is cold (or so the ECM thinks) and operates accordingly. Closed loop monitors the sensors to give you the best performance, which means more power and more MPG.

I recall seeing some gain 2 MPG by switching from a 160 to a 195 degree thermostat. if that is true, that's 60 miles per tank you are missing out on at $3.00+ a gallon!

 

[JPOutfitters]

looks like I need a 190-195 thermostat!

 

[brsampedro]

ill check pressure and get a test light on injectors this weekend,ive been going at this alone as many of u see the difficultys of that but will post again sat night or sun, thanx for your help jj , i never thought to use test light to check power at injectors while cranking...

about the themo post , i live in south fl. here most older cars like my 84 c-10 we use no thermostats, i had one in truck when i bought it but when i blew radiator n hoses i replaced whole cooling system and went w/o one no probs and this was last june , then again im far from freezing temps my prob here is over heating but she never does

 

[Jessie James]

Most Chevy 350's operate at peak efficiency in the 200-212 degree range. You don't have to run a thermostat, but you are cheating yourself out of power and mileage.

From http://www.arrowheadradiator.com/preventing_cylinder_head_gasket_and_cooling_system_failures.htm

Most cars and light trucks since 1971 require thermostats with 192 or 195-degree ratings. Using a cooler thermostat (160 or 180 degree) can increase fuel and oil consumption, ring wear and emissions. On newer vehicles with computerized engine controls, the wrong thermostat can cause major performance and emission problems if the engine fails to reach the proper operating temperature.

The heat of the engine also helps prevent acid formation in the oil, burns off excess vapors, and removes condensation which turns your oil to sludge. In addition, the heat helps prevent exhaust condensation which will rust our your exhaust system sooner.

So, lower coolant temps are just causing more wear and less performance all around. You won't know until you go 100k miles and have to do a rebuild, when someone running a higher temp can just keep changing the oil. In the terms of MPG, you are throwing away money every time you fill up at $3.00+ a gallon.

I used to run a 160 thermostat in my cars when I was younger, but someone pointed out that engines have a thermostat for a reason and me second guessing over 100 years of research and development by putting a non-stock thermostat in makes me the fool. It turns out that the 160 degree thermostat was used for alcohol-based coolant. Am I really smarter than thousands of mechanical engineers who have tested thousands of cars over millions of miles? No, I am not, but I am learning!

 

[only 31s]

maybe ignition module

maybe the ignition module, or the reference wire[purple and white]might be twisted or loose at connection-that module is in the cap and can blow at any time for any reason-controls info to comp to tell it when to fire injectors

 

[brsampedro]

had a couple hours this weekend to check things out, found while cranking test light would dull out , fuel pressure is where it needs to be, also found a loose ground on bell housing coming from harness which distributer wire go into there are two ground wires connected to the bell housing but was loose re grounded it and nothing still, had icm checked at autozone and it passed all test , waiting for a day off to completly go through system, will be back sorry for delays but thanxs for patience