Help us stop throwing money at this misfire and hesitation, Please!!!

[neemo6]

My dad has a 92 c1500 silverado a/t, 350 5.7l, tbi. Problem he has is that it hesistates and misfires pretty bad once you accelerate. There is no check engine light. Ok everything that has been changed due to thinking it was the cause of the problem. Fuel pump, fuel filter, cap and rotor, plugs and wires, egr valve, map sensor, timing chain, and as of yesterday the injectors themselves . Fuel pressure checked out to 14psi, timing was set dead on. It will hesitate and misfire when you rev the engine but if you spray some starting fluid will rev up fine and stop the misfire. Also a snap on diagnostic tool ran a back up spark and fuel test and the truck runs flawless and revs up fine while the test is running. What could possibly be causing this? Im all out of ideas and tired of just throwing money at it. Can a bad ecm cause this? Please help!!!

[MT-2500]

Is it a dead miss or just rough or miss fire?
Double check cap rotor and wires and plugs and coil base timing.
Good hot blue spark to all plugs?
One idem to check real close along that year is dist shaft busking wear.
Remove the cap and see is the rotor or dist shaft has any side ways play.
If lose it is time to fix dist.
And yes PCM can cause it.
Also run a tap test on the pcm or drop it down and do a twist test on it.
If taping or twisting it changes engine running replace the pcm.

[neemo6]

It is a rough misfire. Ya im getting good spark on all plugs. Ill check out the dist shaft tommorow since its storming out today.How do you go about doing a tap and twist test on the ecm? Thanx for your help.

[MT-2500]

Take your knuckles and give it a tap or grab a hold of each side and twist it.
The idea is to test a cracked circuit board or lose joint.

[neemo6]

Messed with it some more today, noticed that when we rev the engine some of the gauges move when they shouldnt be moving such as the speedometer when standing still. Also the truck runs fine when in limp mode, we got it to get into limp mode via the diagnostic tool. Is there a way to get it into limp mode w/o the tool? Why does it run better in limp mode than when in its normal mode?

[MT-2500]

Limp mode is a get home mode if the regular part of pcm fails.
Goes to base settings.
If all sensors readings are ok and working ok then you have a bad pcm.
Scan tool is the only to get limp mode.

[neemo6]

That is what I was suspecting, since almost every sensor has been replaced new or swapped with a working one from another silverado.