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Revived ‘91 TBI running poorly

76k5blazerr

76k5blazerr

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Picked up a 1 owner 91’ blazer from a guy I know recently, his mom passed and it was part of the estate. Off the road since 09 and basically moved around the driveway until 2018 when they took it to storage where it sat until I got it.

So far I have replaced the tank, sending unit and pump, distributor and coil, plugs and wires and first cleaned the injectors best I could. After this it runs on its own but it still had fueling issues, wants to die out if you give it more than about 1/4 throttle. Just chokes and stalls. I figured the injectors were plugged beyond repair, they were pretty much just dribbling fuel not spraying it.

Replaced injectors today and I can see them spraying now but it’s still doing the same stalling out. Seems to maybe idle worse now.

I should mention I have changed the fuel filter as well.

I have not checked fuel pressure, and I won’t rule out a crappy new pump, but to me it sounds more like a delivery issue farther up the line. I understand how tbi works, I still have my 89 but it has never given me the first lick of trouble so I haven’t had a chance to tear into it.

What y’all think?

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Check for vacuum leaks.

If the previous injectors were dripping fuel the new plugs may be fouled.

Iac motor may be sticky, partially clogged and or blocked from seating.
 
Sorry, I was thinking fuel pressure regulator
 
Fastereddie said:
Sorry, I was thinking fuel pressure regulator
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When I had the injectors out the first time to clean them I replaced the gasket for the regulator, not much in there but a spring. I guess it could still be the problem but not sure how to pinpoint it as the exact problem
 
Nice Blazer! Nobody on this site ever lives near me. I have TunerPro software set up for a 1991 V series truck with all the proper .BIN and .DEF files to interface with your ECM, in order to see what you engine is doing since I own a 1991 V series crew cab myself, but that does no good when you are 3000 miles away.
 
Keep running fuel through it and keep cleaning or replacing things that get gummed up with old fuel varnish. Good fuel and some injector cleaner. I have brought a few TBI trucks back from the dead. You have changed the obvious stuff. Without changing everything your best bet is to keep putting fuel through it and keep trying to drive it. Mine have cleaned themselves up over time. The more you drive it the better it should run. 1989 suburban and 1990 Blazer both needed some time to clear up, several tanks of fuel. My 1991 suburban was just a little rough when cold and it cleared up after some daily driver duty. Check the vacuum lines and TBI base gasket too.
 
HankScorpio said:
Keep running fuel through it and keep cleaning or replacing things that get gummed up with old fuel varnish. Good fuel and some injector cleaner. I have brought a few TBI trucks back from the dead. You have changed the obvious stuff. Without changing everything your best bet is to keep putting fuel through it and keep trying to drive it. Mine have cleaned themselves up over time. The more you drive it the better it should run. 1989 suburban and 1990 Blazer both needed some time to clear up, several tanks of fuel. My 1991 suburban was just a little rough when cold and it cleared up after some daily driver duty. Check the vacuum lines and TBI base gasket too.
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It has fresh fuel and a can of sea foam in it right now. Heavy sea foam mixture. I was just surprised when it almost ran worse with the new injectors.
 
Check the voltage back at the pump. Or I should say at the connector on the frame rail before the pump. I’m going through the same issue of not enough fuel pressure, but have found I don’t have 12volts at the pump.
 
Jimmy85 said:
Check the voltage back at the pump. Or I should say at the connector on the frame rail before the pump. I’m going through the same issue of not enough fuel pressure, but have found I don’t have 12volts at the pump.
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Interesting. How did you check your fuel pressure? Haven’t messed with the truck since I put the new injectors in but I will get back on it tomorrow and hopefully make some progress.
 
Ok, I'm starting to really suspect the fuel pressure regulator and the pump now. Tried to start the truck tonight to move it to where I can work on it, and now it won't even stay running on its on. It fires up, then dies out almost immediately. Before it would do this a couple of times and then it would stay running on its own and wouldn't die out unless you floored it. Im unfamiliar how the FPR on these units works, but I did change the gasket when I did the injectors and I cleaned it out. Does this sound more like the regulator or the pump?
 
When I first rescued my 89, there were many issues with the TBI engine. First it was the injectors leaking. Then the ECU was doing some weird stuff and kept going bad. Couldn't spot until you hooked up a scanner to the ECU. You can clearly see the injector leak when it was running. It was hard to start and hard to keep running. Good fuel pressure is another good test and should point to a bad regulator if that does exist or a bad pump.

After all of that, I ended up replacing the engine since there was concern the cam was flat and it did have head gasket failure too.
 
This might be a long shot but any chance you have a plugged catalytic converter?
 
I won’t rule out anything at this point, but the engine does sound healthy when it runs. Before the new injectors once it was running it idled great just would choke out when you gave it gas. Wish it already had a schrader valve to check fuel pressure but I guess I’ll have to buy the adapter and test that.
 
So tonight the truck decides it wants to run again, well at least idle. Still dies when you rev it. So I had my buddy rev it while I sprayed starting fluid down its throat. It revved normally… so even without a fuel pressure test we have identified the problem I believe. I’m leaning toward the pump because I bought the whole unit off Amazon for 70$ because it had next day delivery. Yeah I know, stupid. But it had decent reviews. It does sound very whiny though. Guess I need to order another one and drop the tank again. Dammit.
 
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