Have to bump throttle to keep running. Won't run at any steady RPM.

[Hoot Gibson]

I haven't (seriously) turned a wrench since carburetors and points, so I'm at a loss.

1994 C1500 Silverado 350 TBI automatic. Seldom used ethanol.

The truck sat for 6 months or so. When I tried to start it, it did the below. I drained the gas, put in fresh, and changed the fuel filter.

It starts and dies immediately. Does this every time. However, if i bump the throttle at start, it will raise the RPMs. Then it dies. If I bump the throttle continuously, it will keep running. It won't run at a constant RPM, I have to keep revving it up and letting it come down, then rev it up again before it dies.

Any ideas? Thanks in advance!

 

[Schurkey]

1. What is the fuel pressure?

2. How old are the usual "tune-up" parts--cap, rotor, plug wires, plugs, PCV valve, air filter?

3. Connect a scan tool, look at sensor data--IAC motor especially, then MAP, Coolant temp, etc.

 

[Hoot Gibson]

I'm hoping to check fuel pressure tomorrow. A buddy is supposed to bring his testor.

Changed PCV valve a couple of days ago. Air filter is clean. Other parts are kinda old. The truck was running fine before it sat too long. Inside the distributer looks good, plug wires look good.

Don't have a scan tool. Gonna check OBD 1 blinks tomorrow.

Thanks!

 

[Nad_Yvalhosert]

You NEED one with a live data stream. Find a shop.
The flash codes type wont get you anywhere if there are no codes present.

Case in point: my '88 would stall when it reached closed loop. No codes. Ran perfect in open loop.
With a datastream I found the ECT at -40°. 1 new temp sensor in the intake, 3 mins of labor, and no more problem.

 

[someotherguy]

Low fuel pressure and bad CTS are high on the suspect list; concentrate testing efforts in the areas those guys mentioned.

Richard

 

[Hoot Gibson]

No info from the OBD1. No surprise there, I had the battery disconnected yesterday repairing grounds. Ran the engine (bumping throttle) for a while, and still no codes.

Nobody around here (south Mississippi) makes house calls. Any suggestions for a scanner that is relatively affordable (under $250)? I'm in the weeds here, and have no idea what I'm looking for. I found obd1dotcom suggests a laptop and software. Is that a viable idea?

Waiting on my buddy to check fuel pressure. Other than that, I'm at a standstill.

Thanks!

 

[someotherguy]

Suggestions? Buy a fuel pressure test kit as it will serve you well in the future if you keep TBI vehicles. A low scale on the reading would be good as operating pressure spec of your engine is 9-13 psi. The trick is finding a gauge set that will work with TBI. It requires a special adapter, or you can sort of hack one together with some scrap hose, clamps, and a T fitting. The one I like, the Actron CP7817, is discontinued - but used to be available for the cost some people sell the adapter fitting for separately. Don't spend $25-$30 or more on the adapter.. check Actron part # 0180-000-1320 - they offer it at $7.89; Summit has it for $14.99, regardless of where you get this part this is the type of adapter you need for TBI fuel pressure testing. Here's a writeup I did on Chevytalk about fuel pressure (and also spark testing, which isn't applicable in your situation) https://www.chevytalk.org/fusionbb/showtopic.php?tid/253427

Next up, you can test your CTS with a regular ohmmeter/multimeter. Here's a thread with the values you can expect from a good CTS depending on coolant temperature, look down in the thread a few posts -> https://www.chevytalk.org/fusionbb/showtopic.php?tid/176155

CTS's go bad over time and will read "colder" than normal, and cause a rich mixture that will eventually get so bad it can fuel-foul the plugs and stall the engine.

Richard

 

[Hoot Gibson]

Thanks Richard! Turns out my buddy doesn't have a fuel pressure tester, so I ordered one. I'll check the CTS tomorrow. I have a digital multimeter, and I'm pretty familiar with using it.

 

[Schurkey]

No info from the OBD1. No surprise there, I had the battery disconnected yesterday repairing grounds. Ran the engine (bumping throttle) for a while, and still no codes.

No "codes" doesn't mean there's no "info".

"Codes" can be useful. Data stream is essential.

Any suggestions for a scanner that is relatively affordable (under $250)?

When I was spending my own money, I bought a Snap-On Solus Pro, used, from eBay. About $350 shipped to my door with enough accessories, and new-enough (8.2, good to 2007 model year) to do almost everything I need.

What you can get for $250, I can't help with.

Thanks Richard! Turns out my buddy doesn't have a fuel pressure tester, so I ordered one. I'll check the CTS tomorrow.

Did you get one with a TBI fuel system adapter? "Most" fuel pressure testers won't connect to a TBI system unless you buy an adapter along with the tester.

The downside to that, is that the adapters may not have the same sized Schrader valve assembly that the tester is built to thread onto. Be careful.

I have a digital multimeter, and I'm pretty familiar with using it.

Unless you plug the multimeter into the (correct) wires in the molded connector that bolts to the side of the computer, you're testing the sensor, but not the wire harness. Failure of the sensor, or failure of the wire harness look the same to the computer.

Which is why the scan tool is so essential--the computer tells you what it's receiving from the sensor; which includes the wire harnesses for each. You can verify ten sensors, AND their harnesses, in little more time than it takes to do one sensor with a multimeter.

 

[PlayingWithTBI]

I'll check the CTS tomorrow. I have a digital multimeter, and I'm pretty familiar with using it.

An easy way to check your CTS is check resistance at ambient temp, then dunk it in boiling water, and check again.

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