Why is my 1995 running so sluggish?

[Hedden9969]

I have a 1995 c1500 5.0 with 180k miles. I have replaced the Knock sensor, egr valve, egr vacuum solenoid, map sensor, plugs, temperature sensor, fuel filter, removed the throttle and cleaned it replacing the gasket of course. I have checked for vacuum leaks. The truck is still lacking power, very sluggish when accelerating. I can feel surging when under a load. Idles great, revs fine. The exhaust smells like it's running really rich. I'm getting a random cel for knock sensor and am getting a lot of spark rattle. I have checked the spay pattern of the injectors, the pulse is good as is the spray itself, no sign of leaking injectors . I'm really out of ideas here. Any suggestions?

 

[Cadillac Bob]

You check air filter? Maybe a plug wire is bad they can get burned up quicker than you think

 

[Nad_Yvalhosert]

What is the timing set at?
Have you checked for a stretched timing chain?
Pull #1 spark plug at set the engine at true TDC on the compression stroke. Then pop the distributor cap and see where the rotor lines up.
You can use a breaker bar on the crank bolt and rotate the engine forward and backward to see how many degrees it will move before turning the camshaft (and the distributor)

 

[Schurkey]

You've replaced a bunch of parts, apparently without doing any diagnosis whatsoever.

I get replacing the plugs, fuel filter and cleaning the throttle body. I might have also replaced the O2 sensor. All the rest of what's listed should have been checked/verified first, before replacement.

"Rich-smelling" exhaust is generally misfire; and it often leads to a failed catalytic converter. If the exhaust is restricted for any reason including a melted catalyst, and not all the cylinders are running, it's no surprise that the engine is down on power.

Verify all the rest of the usual "tune-up" items--cap, rotor, plug wires, ignition timing including the electronic timing advance, PCV, charcoal canister 'n' plumbing, etc.

Check fuel pressure, under load. Most fuel pressure testers have a button that can be pressed to "flow" fuel out of a plastic hose and into a drain pan, simulating high fuel demand.

Connect a scan tool, verify EVERY sensor and the computer outputs. Given the history of knock sensor problems and actual knocking, I'd be double-sure to check that entire system. Among other procedures, connect a timing light, and then tap a brass or small steel hammer against the iron of the cylinder head. (Tapping the intake manifold also works--but be aware that the intake manifold is aluminum. Don't whack it so hard that it cracks.) You should hear the idle drop and then recover, and see the timing retard and then recover, as the knock sensor/computer/wiring harness/ignition module pulls spark advance to "eliminate" the "knock".

Check for restricted exhaust.

Keep in mind that a 305/5.0 is a turd in stock tune.




About a thousand years ago, when I was pre-teen and teenaged, I knew a guy named Ron Hedden. But he'd have been on the other side of the country from you. Last I heard of him, he was in the San Fran area; and if you're related he'd probably be your grandfather...or great-grandfather; and I'm sure he's dead by now.

 

[L31MaxExpress]

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Scan tools

im looking into buying a new scan tool that will do a crank relearn and read live data. I have an apple or id buy the OBD link. What are you guys using? Looking to spend $200 or less.

www.gmt400.com

#JustUseThePaperClip *

Alot of people do not know that shorting A-B does stuff beyond that. If you leave the code key in place, start the engine the ECM goes into Field Service Mode. In addition to other things the Check Engine light will indicate when the 02 sensor is rich or lean. When you first start the engine it will have a steady blinking SES light. When the engine warms up assuming it goes into closed loop, the light will stop the steady blinking. It will go into a seemingly random pattern of flashing. It is blinking in response to Rich/Lean. If the light is on the 02 sensor is above the threshold to indicate rich. If it is below the threshold it will be off to indicate lean. I would not recomeend making a WOT pull in Field Service Mode but the vehicle can be driven at light to moderate throttle. If the light stays out most of the time the 02 sensor is indicating it is lean. If the light stays on most of the time the engine is rich. "RICH" is not a smell, unburnt hydrocarbons are what you smell. An engine that is running lean will have a stronger unburnt hydrocarbon smell because it is nearly constantly partially or fully misfiring on some or all cylinders. You would have to have the engine running insanely rich to have a hydrocarbon smell from an over rich air/fuel mixture which would be accompanied by grey or black smoke. Think carburetor with the choke stuck fully closed or fuel being forced past the needle and seat straight down the venturi.

 

[Schurkey]

Alot of people do not know that shorting A-B does stuff beyond that. If you leave the code key in place, start the engine the ECM goes into Field Service Mode. In addition to other things the Check Engine light will indicate when the 02 sensor is rich or lean.

But wait! There's MORE!

The speed of the flash indicates open loop vs. closed loop when the engine is running.

I forget which speed indicates which operating parameter. Fast flash might be closed loop. Or the other way around. Details in the service manual.

YES, a person can use a paper clip to do rudimentary diagnostics and code-reading with most OBD1 GM vehicles. But a scan tool does a hundred times more, and without the guesswork.

 

[Erik the Awful]

I remember the days of laying upside down under a dashboard, watching winky lights to try and diagnose a problem. It sucked. The fact that the engineers had the tools to read data stream, but refused to release them to even dealership technicians at the time still pi$$es me off.

Yes, you can pull trouble codes with a paperclip. You can also sit on your hand until it goes to sleep and play "the Stranger". Buy a scan tool.

 

[Schurkey]

^^^ Fookin' priceless. Frighteningly accurate.

I have the sense that I ruffled some feathers on this site when pretty-much every post I made was "check fuel pressure, connect a scan tool and look at the data stream--verify every sensor..." But working on computer-controlled vehicles without being able to interrogate the computer is two steps away from hopeless.

 

[PlayingWithTBI]

You can also sit on your hand until it goes to sleep and play "the Stranger".

LOL, I like the "Gone in 60 Seconds" reference.

 

[L31MaxExpress]

^^^ Fookin' priceless. Frighteningly accurate.

I have the sense that I ruffled some feathers on this site when pretty-much every post I made was "check fuel pressure, connect a scan tool and look at the data stream--verify every sensor..." But working on computer-controlled vehicles without being able to interrogate the computer is two steps away from hopeless.

I had a very simple interface I built back when laptops had a DB9 Serial port. Software was named WinALDL. Worked on all the older GM stuff with a 160 baud rate. Back then it was $20 in materials and 20-30 minutes to build it. Now you can buy a GM OBD1 to USB cable for $50 and use TunerProRT to datalog ANY of the OBD1 datastreams, both 160 and 8192 baud are supported.