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89 Blazer sputtering issue...

Rally Smith

Rally Smith

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My Dad has a 89 Blazer 5.7 auto that has been getting worse and worse. For some time now, while driving it hesitates for a split second and repeats every 10 seconds or so. It has gotten to the point that he's not confident that it will actually keep running if he goes into town.

He has replaced all vacuum lines, sprayed around manifold and TBI will no leaks detected. We found the distributor rotor moved side to side so it was replaced. Plugs were pulled and they looked great but replaced anyway.
Found a plug boot arcing to heat shield. Temporarily repaired to see if that was the cause. Not the cause. I checked for codes and there are none.
TBI is spraying nicely so that can't be it. So at this point the only thing that I can think that may be the problem is it needs new plug wires OR the knock sensor is retarding the timing because of an exhaust leak at the manifolds.

Anybody have more things to check?

Thanks,

Rick
 
Put a fuel pressure gauge on it. Autozone will loan them for free.

Can't comment if low pressure can be seen based on injector pattern, but getting progressively worse sounds just like the in-tank fuel hose.
 
How does that work? I've got adapters and fuel pressure gauge before and attached it to the inline tube going into the back of the TBI. Not sure how what your describing would work.
 
The kit I have actually goes in place of the fuel filter, you remove the filter, put the adapter in it's place.

It's really difficult to tell looking at the spray pattern if the pump is pushing enough pressure, it needs more pressure when the throttle is applied, the pump may not be giving enough at that point. I fought this several years back with mine as well, also if you try to force it to move with more throttle it'll sometimes spit out the intake. Usually gives a lean code/check engine light too.
 
If it's the adapter type, I did it at the fuel filter. Way less risk than doing it at the TBI and IMO easier to access. Replacing the whole fuel filter would be a lot easier sounds like.

I would go with what others who have dealt with low pressure on TBI say. It's already pretty low pressure, so if you can't necessarily tell from spray pattern, just check it.

I checked pressure before/after the fuel filter as well while I was under the truck, to make sure it didn't need replaced.
 
Water in the fuel can cause a lot of grief thats hard to diagnose...try taking a fuel sample in a glass jar,see if any water is in it...it might look milky rather than separate and settle to the bottom if your using ethanol gas..it tends to keep the water mixed in..
 
It has a new fuel pump and filter. I hadn't thought of the gas/water issue.
I'll have to have him check that.
 
No clue on what's going on. Taking it in next week. I'll post back what the problem is/was.
 
I’m still trying to figure out the problem before the Blazer goes in on the 30th to save money.
I’m trying to check the EST system. My Haynes Manual has some information but doesn’t explain to near the extent it should.
It says:
The ECM will set EST at a specified value when the diagnostic test terminal in the ALCL/ALDL connector is grounded. To check for EST operation, the timing should be checked at 2000 RPM with the terminal ungrounded. Then ground the test terminal. If the timing changes at 2000 RPM, the EST is operating.

My question’s on this is:
1) What diagnostic test terminal in the ALDL connector needs to be grounded to set the EST?
2) When checking EST operation at 2000 RPM’s what and where do I make sure that the test terminal is grounded and ungrounded?

Thank you in advance,

Rick
 
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