87 TBI troubles, please help

[AyWoSch Motors]

I'll try that

 

[AyWoSch Motors]

So in re-reading your first post this started happening after doing the ignition system work, and I reading that correctly? I'm wondering if you got a new module that isn't giving the computer a strong enough RPM signal? If you have a spare I'd swap it out just to see, especially if it was lower cost or off brand module.

Make sure that none of the wiring is damaged where the injector wiring leads to the injectors especially where it passes from the outside to inside the throttle body sometimes it gets rubbed in that little rubber bushing it passes though or someone damages it putting the air cleaner one, some times it take a while for a wire crimped for that to actually become a problem so if one or more of the wires has been flattened even if it didn't break though the insulation it could be a problem. Feel free to post pictures of the wiring and engine it might not tell us anything but maybe we'll spot something.

I checked that those wires weren't damaged, they look to be in good shape.

This all started when it stopped running, did work to it to try to get it running again.
I didnt replace anything in the TBI, just took it apart to clean and inspect it.
Which Module do you mean?.

 

[AyWoSch Motors]

Ok here's another thought for you. There should be some ground wires attached to a stud on the thermostat. These ground wires the computer uses. The injectors are constantly fed power, and the computer completes the circuit creating the pulse though those ground wires at the thermostat.

Hmmm, didnt know that. I will have to inspect it.
On the thermostat?

 

[SirRobyn0]

Hmmm, didnt know that. I will have to inspect it.
On the thermostat?

Yes, IIRC one of the two bolts that holds the housing down is a double stud with a nut, should be some ground wires on that but I think the number varied from year to year.

 

[WP29P4A]

My son's 87 TBI truck has that ground, it was covered in oil and it was lose. I pulled it off cleaned and tightened it. Truck ran more consistent after.

 

[Originalthor]

There are also two ground wires on the back of the passenger side head aswell. Also just on a whim here check the bulkhead connection at the fire wall. Theres some wierd tar stuff in there thats like to hinder connections.

I just did a stand alone harness on my tbi and it runs 10 time better once I redid those grounds and just give it 12v power straight from the battery. So I'm assuming it was something to do with those grounds and bulkhead connection.

 

[Redfish]

On the back of the engine, right against the firewall and partially hidden there is an oil pressure switch. It is tied into the FUEL circuit and will not let fuel get to the engine if there is no oil pressure. I haven't looked at a schematic to see where it ties in but I do know what it does. On my all stock '87 when I turn the key I can hear the electric pump come on and prime but the engine won't run if that switch is bad.

Just a thought.

If you do replace that switch pay careful attention to the plumbing it is attached to. Otherwise you will find yourself using an EZ Out to remove a piece of broken brass pipe and raiding Home Depot to fabricate a new pipe and elbow assembly.

 

[AyWoSch Motors]

Okay, I'm going to liven this thread one last time, see if any new Ideas pop up..
I now own this truck, so it's my problem now.
I'm going to give fixing the TBI one last try, before throwing a carburetor on it and be done with it.

Out side of that, anyone else swap a carb onto a TBI square? Any pointers or things I may have forgotten?
I think I have everything I need.
I have a 4bbl cast iron inake with tte slots cut and wedge washers for TBI heads, a Quadrajet, new HEI dizzy, mechanical fuel pump and fuel pump pushrod, and a set of mechanical pump style sending units. Anyone else think of what I might be missing?.

 

[SirRobyn0]

@AyWoSch Motors Ayden, let me make sure I fully understand. So basically I re-read the thread and truck will run if you provide fuel another way.

So it you be really great if you could get a fuel pressure reading when the truck won't start. That would help you to figure out if it is a supply issue, or the ECM not enabling the injectors. Because those are the only two possibilities. Look I get it a running carbureted truck is better than a FI lawn ornament, but the throttle body injection does have advantages.

IF you think it's not getting proper fuel delivery you could try bypassing the electrical wiring for fuel pump.

When the truck won't start I assume you cannot see fuel being sprayed out of the injectors? IF the truck has a fuel pressure test port hook a gauge up to it. If you don't have gauge push on the shrader valve and see if you get a good stream of fuel out or just a dribble. You might just have a bad pump.... IDK. I get your thinking on switching to a carb so the darn thing will run, but if you can get this thing to run reliably TBI that would really be best I think.

 

[AyWoSch Motors]

@AyWoSch Motors Ayden, let me make sure I fully understand. So basically I re-read the thread and truck will run if you provide fuel another way.

So it you be really great if you could get a fuel pressure reading when the truck won't start. That would help you to figure out if it is a supply issue, or the ECM not enabling the injectors. Because those are the only two possibilities. Look I get it a running carbureted truck is better than a FI lawn ornament, but the throttle body injection does have advantages.

IF you think it's not getting proper fuel delivery you could try bypassing the electrical wiring for fuel pump.

When the truck won't start I assume you cannot see fuel being sprayed out of the injectors? IF the truck has a fuel pressure test port hook a gauge up to it. If you don't have gauge push on the shrader valve and see if you get a good stream of fuel out or just a dribble. You might just have a bad pump.... IDK. I get your thinking on switching to a carb so the darn thing will run, but if you can get this thing to run reliably TBI that would really be best I think.

I agree, although it always seemed a tad bit ball-less when it did run with the TBI.

Do TBI fuel lines have a test port? Never seen one.
I could also undo the out going fuel line from the tank, and see if it comes on like it should. Luckily I can get to the top of the tank easily without removing the tank, thanks to the flatbed.

 

[Rusty Nail]

i'm at fuel filter.
open end 5/8 and one inch wrenches needed. located on passenger side framerail halfway down.
prolly cost 5-7 bucks
might need a 10mm for the bracket

be sure to write the date on it.
life expectancy is about 2 years / 30k miles...how many did you say it's got?
remove gas cap prior to replacement. gas exits towards rear bumper upon loosening - be advised. tie a rag around your wrist and thank me later.


bonus fun! learn to sell fuel filter service!

remove filter, try to keep gas in it.
plug openings with thumb and middle finger.
tap it on the ground a few times.
pour contents into clean container and sell the filter using the gas that comes out of it visual.

unleaded gas is pink or purple, not brown like the garbage your engine is trying not to have to burn.

ew.
the $80 service will sell itself and it takes about 15 minutes.

while you have it off? turn key on and see volume. catch it or lay in gas.


never done it before though, I saw a video, that's all. you'll have it down - the second time around.