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Old 10-07-2018, 12:51 AM   #1
69ARROWHEAD
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Default '96 Tahoe with hesitation under load issue

Hi everyone, this is my first post . My dad has a '96 Tahoe with the 5.7 Vortech and 118,000 original miles. This vehicle has been very reliable but have recently been stumped with a drive-ability issue. The engine starts, idles, and drives perfectly, but once it begins to reach normal operating temperature it begins to act up. From a dead stop, the engine seems to bog down or feel sluggish. The RPM's drop slightly from about 2000 RPM to about less than 1000. If i really put my foot in it from a stop it feels more drastic of a bog or stumble. I can't say this happens from a 1-2 shift or 2-3 shift because it is not consistent. If I ease into the throttle from a stop it will accelerate and shift normally and can get it to drive somewhat better but the stumble will happen once I get past 2500 RPM. I hope I am describing my my problem clearly.

So far I have checked, changed or confirmed the following:
There are absolutely no trouble codes but it did have an oxygen sensor code about the time this problem started intermittently and only happened maybe once, then ran fine. It now Bogs or struggles as described on a consistent basis. Absolutely No codes now.

Replaced fuel filter

Checked fuel pump, pressure is ~50 psi KOEO. It will drop to 48 psi min with engine running and will raise to a little over 55 when i give it some throttle. Driving, it does not drop below 48psi.

I have completely disconnected the exhaust pipes at both manifolds to confirm catalytic converters are not clogged.

Switched out ignition module with another used piece.

Switched out ignition coil with another used piece.

Transmission was rebuilt 3 years ago and to me "feels" like it's shifting well. I had my transmission guy drive it and he seems to think it is an electrical problem. Trans fluid is cherry red and clean. I noticed a slight leak around the transmission pan gasket but there are no spots on the driveway.

I am very mechanically inclined, I am the only one that has done any repairs to this Tahoe all of it's life. Even the transmission, I personally removed the transmission and took it in for a bench rebuild, and then I re-installed (3 years ago).

Bottom line, no change after all checks indicated above. Engine idles smooth as can be ~550 RPM. If I put it in park and rev up to 2000 RPM's or more, engine seems smooth with no missing or hesitation at all. No drop in RPM with no load on it.
Any suggestions appreciated.
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Old 11-13-2018, 08:59 PM   #2
idahojdk
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have you resolved this?? I am running into the same issue.
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Old 11-13-2018, 11:49 PM   #3
Mc_99z71
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Check the fuel psi specs, I know vortecs injectors need enough pressure to spray properly. I may be wrong but I thought it had to be 55psi-58psi ? My 99 tahoe lately feels like its lost a bit of power under light load around1500 rpm and my fuel pressure is at 52psi and it used to be 59psi so Im thinking that could be the cause.
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Old 11-15-2018, 03:53 PM   #4
steviemack336
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Check distributor rotor and cap helped me with mine

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