95 Sierra no power

[Cdavis95Z71]

Hey guys, I know this questions been asked a thousand times but I’d rather ask you guys myself, so I have a 95 Sierra z71 and I’ve put a lot of work into it but over the past few months it’s begun to run really rough, it stumbles a lot and has no power. It’s got new plugs, wires, coil, EGR, new heads and head gaskets as well as all the other top end gaskets, radiator, fan clutch and I put headers on it last week. I do have a Holley 670cfm TB I’m installing this weekend. Other than those parts what other stuff do you guys suggest replacing? Even if it’s not engine related, any parts that can help the truck last a while as it only has 150k miles on it. I got a new truck to get me to work and I really want to get my 95 Z71 running strong again so I can enjoy it on the weekends. Any info helps!

thanks, Carson

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[east302]

No experience with a TBI, but fuel pressure and restricted exhaust (damaged catalytic converter) are a couple of things to check.

Are any codes being thrown?

 

[Nad_Yvalhosert]

Before you load up the parts cannon, figure out the running issue. TBI systems are pretty rudimentary. The codes, if any, dont diagnose any problems. They merely point to the general system. Its up to the mechanic to go through a flow chart.

As an example, my '88 5.7 ran terrible in closed loop, but started perfectly when cold. No codes, but turned out the temp sensor was reading -40°C.

Get a scan tool and start looking for erroneous data.

Second, rust/corrosion and bad ground wires. With age, heat, and vibration, wiring gets brittle. Look well at the harness and the multiple ground eyelets.

 

[Cdavis95Z71]

No experience with a TBI, but fuel pressure and restricted exhaust (damaged catalytic converter) are a couple of things to check.

Are any codes being thrown?

No codes are being thrown, just running rough

 

[PlayingWithTBI]

fuel pressure and restricted exhaust (damaged catalytic converter) are a couple of things to check.

^^^X2, check your fuel pressure - s/b 10 - 13 PSI. The higher the better.

Get a scan tool and start looking for erroneous data.

^^^X2 a scan tool is the best way to go but, it won't tell you what your fuel pressure is. Another well known and documented issue, here and other forums, can be you ICM and/or coil which the scan tool may not indicate.

 

[1997]

you probably know this, but just in case, 95 is OBD1, codes can be set without turning on the check engine light.
nice looking truck.

 

[Schurkey]

Stop replacing parts, and especially don't install an aftermarket TBI unit.

Fix the truck FIRST, before you modify it.

Verify fuel pressure.

Connect a scan tool, look at the data stream. "Codes" are useful, the data stream is ESSENTIAL.

Verify the intake gaskets--I had that problem last summer. Intake gaskets squeezed out of position, lead to an air leak into #1 and #3; and would have caused problems in other cylinders shortly. I discovered which cylinders weren't running right by performing a cylinder-balance test. From there, it was just a matter of figuring out WHY those two cylinders didn't run at idle.

How old are the cap 'n' rotor?

Engine ignition timing done correctly?

Are the "new" plug wires routed correctly? Especially important to keep #5 and #7 routed exactly the way it was done by GM.

 

[Ruff Idol]

Having a similar problem when I give it even a little pedal. I'm thinking it's the TPS. That seems to be a common cause of hesitation, and like you, already did a basic tune-up and whatnot. Check for vacuum leaks as well

 

[WB23]

Stop replacing parts, and especially don't install an aftermarket TBI unit.

Fix the truck FIRST, before you modify it.

Verify fuel pressure.

Connect a scan tool, look at the data stream. "Codes" are useful, the data stream is ESSENTIAL.

Verify the intake gaskets--I had that problem last summer. Intake gaskets squeezed out of position, lead to an air leak into #1 and #3; and would have caused problems in other cylinders shortly. I discovered which cylinders weren't running right by performing a cylinder-balance test. From there, it was just a matter of figuring out WHY those two cylinders didn't run at idle.

How old are the cap 'n' rotor?

Engine ignition timing done correctly?

Are the "new" plug wires routed correctly? Especially important to keep #5 and #7 routed exactly the way it was done by GM.

Do you happen to know the original routing pattern for a 98 Silverado 5.0? All stickers under the hood were missing when I purchased it. Thanks in advance.

 

[Schurkey]

Do you happen to know the original routing pattern for a 98 Silverado 5.0? All stickers under the hood were missing when I purchased it. Thanks in advance.

It'll be in the service manual. That's where I found it for my '88.