help, no fuel delivery on TBI (1 Viewer)

[tcarlson78]

So I my TBI woes continue, My engine is running poorly, it surges and stalls especially when cold. So today I was trying to track down and eliminate gremlins that thirdgen.org suggested. I was checking for vacume leaks when I bumped the hose going between the PCV and the TBI and and the engine quit. WTF! Up to this point no leaks but I replaced all the vac hoses I could. Tried to start it and nothing, WTFx2! Fuel pump working, check. Fuel gettng to the TBI, check. pressure, ?? Fuel getting to the injectors NOPE. Prevously the injectors were working, a nice cone of fuel.

Short of pulling the TBI off and rebuilding, what can I do to fix it? really want to get it out of the garage today. I am off to the store to pick up some parts that I hope I don't need but could help solve the original problem of poor running engine.

thanks in advance!

 

[cardinal fang]

What fuel pump are you using? I had similar problems until I changed the fuel pump. Now it runs great.

 

[zags]

Remove the electrical connector from the injector. Using a test light connected to ground, have someone crank the engine for you. One side should show constant power. Connect the test light to the positive side of the battery and test the other lead while cranking. The light should flash.

 

[Mr. Toad]

. . . The light should flash.

Very, very fast. Perhaps looking like it's dimly lit.

 

[nicholastheczar]

I would suggest also putting a fuel pressure guage inline so you can see what kind of pressure you are getting. You might also try putting in a clear pre pump inline fuel filter so you can see if your fuel is moving downstream.

Nick

 

[tcarlson78]

I dove in and cleaned and rebuilt the TBI, and installed new injectors. The pressure regulator was checked but not replaced due to parts availablilty. Put it all back together and tried again. Nothing. Thinking about a new pressure regulator assembly or perhaps getting an adjustable one. Any suggestions??

I have a pre and post fuel filter, carter pump I can see fuel moving in the filters. I ordered an inline pressure guage tonight and will hook that up once I get it.

Is there a minimum pressure needed to get through the regulator and injectors?

 

[terrx]

Remove the electrical connector from the injector. Using a test light connected to ground, have someone crank the engine for you. One side should show constant power.

Did you check this already?

With ignition on (key on engine off) each injector should have 12v on one of it's two leads. Depending on year the engine wire harness fuses the two injectors together along with other things (EGR solenoid, etc.).

 

[tcarlson78]

I did check, I have power on one side of each injector. I went out late last night and still no fuel through the TBI. Wondering if not enough pressure.

 

[terrx]

Any updates? Did you get a chance to check fuel pressure?

 

[Mr. Toad]

I did check, I have power on one side of each injector. . . .

But is the other side grounding to complete the circuit and make the injectors squirt?

As far as pressure goes, power your pump and watch your fuel return line. If you have enough pressure to send fuel down the return line, you have plenty for the injectors. Or put in the pressure gauge between the pump and the Throttle Body as you mentioned above.

 

[Trollhole]

1. Take fuel line off of TBI and run it into a bucket. When you turn the key to on does the pump prime and shoot fuel out? If so re install the line and continue.
2. Remove the return line and plum a line from the TBI into a bucket. You may have to do a little more turning the key on and off but eventually you should have fuel coming out in the bucket. If so connect it back up and continue.
3. Check and make sure your ECU actually knows it's cranking. It won't shoot fuel into the motor until it thinks your turning the key. On some TBI systems it's the purple wire. Goes to the circuit the starter is on. So when you crank it sees 12v and knows to start shooting gas. Check for 12v. Also check all other 12v sources going to the ecu. If it doesn't see 12v or greater your going to have issues. If there is continue.
4. Check the distributor and make sure you have spark. If so you can confirm the computer is seeing rotation. Continue.
5. Go buy an inline fuel pressure gauge and install it to the feed line on the tbi and read it while cranking. If it's anywhere around 12-14 psi then your good. If it's low then your pump ain't putting out or your regulator is stuck open which I doubt. If while cranking or running your pressure is above 16psi you either have a bad regulator or your return line is too small.


My bets are on #3 that or the ECU thinks it's in gear or thinks you don't have the clutch in.
4.

 

[kevin colton]

My 78 fj40 w TBI needed a new fuse, which powers the injectors only. You may want to check that fuse, and/or get an OBD engine analyzer real cheap online or @ a local parts store.

 

[tcarlson78]

UPDATE: installed a in line pressure guage. with Ignition on pressure goes to 14lbs then the pump shuts off, like normal. On a whim I flipped the injector connectors and tried again. Nothing. So....

Good electrical power to injectors, good fuel pressure pressure to TBI. No fuel into bowl. However, I do have spark as determined by when I pour a teaspoon of gas into the TBI it fires for a moment. I will get a new pressure regulator tomorrow, and install

Kevin: I don't recall a fuze in my system for the injectors. Though it may have been taped over. I will look.
Mr. Toad: I need to get an assistant (wife) to help me so she can crank and I can test the ground side of the injectors. (that may cost me an extra nice dinner on Sunday)

Troll: with my current set-up the Neutral safety switch is by-passed so no matter what gear I am I can start it up, I just have to remember to have the brake on should I start it in gear However I will track that wire down.(I know, I need to fix it, it is on the list to do when I replace the wire harness)

 

[terrx]

Here're a few more ideas...

Besides trollholes suggestions, go back and re-read this one:

... Connect the test light to the positive side of the battery and test the other lead while cranking. The light should flash.

The idea is that the ECM should be pulling the neg side of the injector to ground each time it tries to fire it. Put the test light between that lead and the battery pos, and crank the motor. If the light doesn't show any activity then the ECM is not trying to fire the injector for some reason. (Be sure you don't accidentally short 12v to that terminal without the test light or injector in between.)

One other thing, this ones kind of obvious but worth asking, did you check for any codes? if it has a check-engine-light, jumper the AB terminals of the ALDL connector, turn the key on engine off, verify if 1) the ECM is working and 2) if any codes are present.

 

[Mr. Toad]

Update?

 

[tcarlson78]

I got back on it tonight. I connected up my WINALDL and turned the power on...No codes but had data coming in. Not overly surprized at this because I had the battery disconnected for a while and that could have cleared the codes plus with the engine not running I dont think the codes will set.

So then I R/R the pressure regulator and re-tested. Nothing. Sweet talked wife out to crank the engine with test light connected to Positive Terminal on Battery and the Negative side of terminal...NOTHING. (yes I see Mr. Toad's Avatar dancing and taunting me)

I traced the wires back from the TBI to the ECU without seeing anything bad. I checked all the fuzes I could find and all look good. Now I am thinking the ECU could be BAD.

Can someone explain a little more on Trollhole's #3. I have a purple wire with a 15a fuze on it and it looks good.

Thanks for any help and additional suggestions.

 

[Mad Chemist]

When I initially installed my TBI, I hooked up the ECU to a wire that didn't get 12V during cranking, only in the ON/run position. So, no fuel during cranking.

Pour a little bit of gas into the throttle body (or spray some starter fluid) and see if it'll start up.

Have you verified that you're getting spark?

 

[Mr. Toad]

...
I traced the wires back from the TBI to the ECU without seeing anything bad. I checked all the fuzes I could find and all look good. Now I am thinking the ECU could be BAD.

Can someone explain a little more on Trollhole's #3. I have a purple wire with a 15a fuze on it and it looks good.

Thanks for any help and additional suggestions.

No taunting here. You now know the ECU is not grounding the circuit to make the injectors fire. So it's time to figure out why. You're on the right track. I would not just assume bad ECU (could you drop another one in there and see?)

 

[Trollhole]

What is your ECU model?

So just to make sure we are correct.

Your fuel pump is coming on during cranking? You verified that?
Your plugs are sparking during cranking? Correct?
You should have 12v going to one leg of the injector connector. You have that correct?


Since you have ALDL connected and the motor is off you can verify the TPS is giving a signal at various pedal positions.

When you crank are you seeing RPM?

If not then I would assume the ignition module is bad.

 

[tcarlson78]

I went out to the local salvage yard and picked up a replacement ECU. Just have to move the chips from the old one to the "new" one connect and try it.

THe ECU is out of an early 90 chevy astro...#1227747 (I used a painless TBI harness kit and that is the one they suggested along with the chips when I originally installed them)
The spark plugs do spark and if I add a little gas into the TBI it will start until the gas is gone.

I need to check the RPM on cranking with the ALDL.

More to come.