TBI - no spray (1 Viewer)

[theo]

Need some help and couldn't think of a better place to ask than Mud.
I rebuilt a '93 caprice engine (350 TBI) and have completed the installation finally (FJ40). I can't get the injectors to open and spray fuel - dry as a bone.

Here's what I have so far:
Code 12 with key on and ALDL pins A and B jumpered. No other codes.
Timing light confirms spark while cranking.
Fuel pressure at throttle body is 12 psi by gauge and is steady while cranking.
Throttle body is filling with fuel as confirmed by pulling the top off.
Test light confirms voltage to injector circuit (and others that need it) wih key on and while cranking.
Test light confirms voltage to "crank" wire while cranking.
Test light confirms voltage to both injectors with key on. (Didn't test it while cranking.)
Fuel pumps run for 2 seconds to pressurize when I turn the key on. (External low pressure pump to 1 quart size slosh tank to external high pressure pump.)

Should I test the injector pulse? A noid light would work to at least show whether there is a pulse, right? But I don't have one. Should I buy one just for this engine?

The manual I'm using says a light across the injector terminals will blink while cranking to indicate a pulse, but they say to use a BT8320 bulb or equivalent. Couldn't find this on the net. Not sure what bulb will substitute. Have read here that a normal test light won't work.

I put a rebuild kit in the throttle body awhile back. Never run this engine so I don't know what shape they were in.

Any suggestions are welcome. theo

 

[Texican]

Any low watt light will work for testing, the most common cause for this is the module inside the dist. so common we don't go any further in testing when we find
good spark-no injector pulse.......
we replace the module.
Butch

 

[Yoda]

Where you at? If near Seattle you can borrow my noid

 

[theo]

Thanks much, Butch. I'll replace the module and post back. Might take a couple hours (or days).

Yoda, I'm in Missoula, MT. Thanks for the offer though.

 

[jrussell]

Check your ground. It was the culprit when I first hooked up my TBI and had no spray.

Good luck!

 

[Markh]

I had the same sort of problem right after I finished the TBI conversion on the V8 in my 40. Does the check engine light go out while cranking? If it does you will need to find a better power source to the computer. The light needs to stay on while cranking or the computer won't send the right signals to the injectors. I had an extra electric fuel pump relay in the garage so I used it to power the computer.

 

[theo]

jrussel, thanks. I spent quite a bit of time on making sure the grounds were good. May have missed something though.

Markh, thanks. I have power to the ECM while cranking (SES light stays on).


Butch and all, I realized last night I have a new ignition module already, came with the new distributor I bought when I rebuilt. Original distributor was missing I now remember. (Ignition module and Electronic Spark Control module are the same, right?)

There is a test to determine whether the ignition module is responsible for not firing the injectors. This is after connecting a light bulb (or noid light) between one of the injector wire pairs and getting no pulse:

- Disconnect distributor 4-way connector
- Ignition "On"
- Momentarily touch harness connector terminal ckt 430 (this is B5 reference pin on the ECM) with test light to 12 volts. Note injector test light should "blink" each time the test light is removed from ckt 430

If you get a "blink" the ignition module is bad.
I got no "blink".

No "blink" means 1 or more of the following:

-Open or grounded ckt 430 (I checked this. Not the problem.)
-Open injector drive circuits (Not sure what this means but I have power to the injectors)
-Faulty ECM connection at B5 or faulty ECM (Connection at B5 seems good)

So I'm left wondering if my ECM is faulty. Also note, when I run the test above the fuel pump cycles each time I touch the 12V test light to ckt 430. Not sure if this is normal but the manual doesn't mention it.

More lost than ever now. Damn.

 

[Yoda]

You did get a TBI distributor, right? I believe the plugs-ins are different, so you should have noticed.

Might be time to get a wiring diagram and see if the harness checks out.

 

[TLCSKULLS]

This is going to sound way kooky, but trust me, it's worth a try. I have the same problem. If I turn the key to where the engine just begins to crank (as opposed to turning it all the way when cranking) the injectors work and it fires up. I have told other w/ chebby TBI have the same gremlin. Have someone crank w/ the key in various positions while you test power to the injectors. Good luck.

 

[Texican]

This is going to sound way kooky, but trust me, it's worth a try. I have the same problem. If I turn the key to where the engine just begins to crank (as opposed to turning it all the way when cranking) the injectors work and it fires up. I have told other w/ chebby TBI have the same gremlin. Have someone crank w/ the key in various positions while you test power to the injectors. Good luck.

Not kooky, there is a wire that should connect to the small terminal of the starter, it is purple in all the kits I used and it supply's voltage to the ECM during starting....a better test would be to use a remote starter switch to confirm as it leaves the ign switch in the run position.......

 

[theo]

You did get a TBI distributor, right? I believe the plugs-ins are different, so you should have noticed.

Might be time to get a wiring diagram and see if the harness checks out.

Yup, factory connectors, etc. The '93 is different than former years; has a broader base where it sits against the block.

Wiring diagram! Been poring over wiring diagrams since the beginning. Couldn't possibly have disassembled the harness and accounted for every circuit without a few diagrams.

 

[theo]

This is going to sound way kooky, but trust me, it's worth a try. I have the same problem. If I turn the key to where the engine just begins to crank (as opposed to turning it all the way when cranking) the injectors work and it fires up. I have told other w/ chebby TBI have the same gremlin. Have someone crank w/ the key in various positions while you test power to the injectors. Good luck.

Not kooky, there is a wire that should connect to the small terminal of the starter, it is purple in all the kits I used and it supply's voltage to the ECM during starting....a better test would be to use a remote starter switch to confirm as it leaves the ign switch in the run position.......

I have the crank sensing wire connected to a circuit I found at the stock fuse block. I will move that connection to the solenoid "hot in start" terminal and see what happens.

BUT, I was under the impression that if the ECM doesn't get a crank signal it stops both the injectors and the spark. Not true?

Thanks, I'll be back in an hour.

 

[theo]

Crank signal wire is connected to the heavy gauge stock Blk/Wht wire that runs from the ignition START terminal directly to the solenoid.

Test power to injectors (has power? yes/no):
Key Off - no
Key Acc - no
Key On - yes
Key On, crank with remote switch - yes
Key Start, cranking - yes

Still have spark to all 4 left bank cylinders while cranking with key.

I'm leaning towards replacing the chip. I'm also thinking that even if the injectors were in bad shape they should still squirt a little. Plus I don't have any evidence of a pulse. (Whoa, maybe I just called myself senile. Not far from it I guess.) Running low on ideas.

 

[Yoda]

Is your TPS good? I know if I hold my throttle "floored" it will shut off the injectors (to clear a flooded condition). If yours thinks it is floored, that might be it.

The wires on ECU "D1" and "A12" is grounded good?

The injector drivers are inside the ECU. The computer provides the ground for the injectors. (ECU pins D14 & D 16 are from the injectors)

 

[theo]

Yoda, thanks for hanging in there! I put it aside for awhile and finished fabbing a fan shroud. (What a fiasco. I can only hope the black paint will disguise it some. )

Late now and tomorrow I better go back to work. But I will check the TPS tomorrow night. And I'll recheck the grounds for D1 and A12. Have a good evening. Back atcha tomorrow or the next day. . .

 

[jrussell]

Since you mentioned rechecking your ground, you might try connecting the two ground leads off the ecm (don't remember the pin #s) directly to the battery. That was how I found that my ground in the harness could not pass a strong enough current to pulse the injector. (I almost did not try this since I had rewired the harness myself and knew? it had good connections. PO had hack the harness off at the firewall.)

Hope you get it figured out, sounds like you are almost done.

 

[theo]

Good advice, thanks. I "know" my grounds are good too. heh heh. I'll try direct to battery to make sure though.

Almost done? I wish. Still have to solve my rear end grind/clunk/howl and rebuild the knuckles. Have an ARB for the front too. Need one of Mark's cages. Need a soft top. Skid plate mods, rear axle vent (easy), center console, stereo install, dual batteries (optional for now), hi-lift mount, tool box of some kind, onboard air, there's more, much more, many more, mucho more.

Cheers, theo

 

[theo]

There are 3 ECM pins that run directly to ground, including A12 and D1. All are wired to a good grounding stud on the body within 18" of the ECM. I have new, heavy ground cable between the battery and engine and between the engine and cab. The only possible bad ground that I can think of now is one of the injector circuits, but the only connections there that aren't stock are the ones I soldered and shrink-wrapped where the fire wall connector used to be. Damn sure I did all of those carefully because I knew I didn't want to go back in there. Pick on this if you like but I'm "damn sure" . . .

I tried cranking with TPS in various positions - nothing. Couldn't find an electronic test for the TPS that didn't require the engine to be running.

I ordered a noid light from Harbor Freight (and a $2 stethoscope! Thanks e9999!). I will retest the injectors for a pulse using proper equipment.

Q: I had the Park/Neutral lead from the ECM connected to ground; thought that was correct. Last night I read somewhere that it should be open. Tried clipping it and still no spray. What should I do with Park/Neutral lead?

still ticking, theo

 

[Texican]

j

- Disconnect distributor 4-way connector
- Ignition "On"
- Momentarily touch harness connector terminal ckt 430 (this is B5 reference pin on the ECM) with test light to 12 volts. Note injector test light should "blink" each time the test light is removed from ckt 430

If you get a "blink" the ignition module is bad.
I got no "blink".

When ya' did this test are ya' sure you had the test light connected to 12v and not ground? I hae seen many of the cheap modules ( like ya' would get in a generic reman dist) bad out of the box.
Butch

 

[theo]

When ya' did this test are ya' sure you had the test light connected to 12v and not ground? I hae seen many of the cheap modules ( like ya' would get in a generic reman dist) bad out of the box.
Butch

Had the test light grounded at first, then realized it and switched to +12. I plan to repeat this test when my new tools arrive. (Bought a Fluke too oh boy oh boy.)

I'll check the price on an ignition module. Got friends at NAPA, maybe can get warranteed but I doubt it. Probably replace it anyway. Thanks again Texas