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

[Schurkey]

Easier still:

Check at ambient temp. If it's way off, replace the sensor.

If it's NOT way off, reconnect sensor, start the engine and let it warm up. When it's fully-warm, shut off engine, test again. If it's way off, replace sensor.

That way, you don't open the cooling system unless you have to.

But this still isn't catching wire-harness faults.

 

[Hoot Gibson]

Hello Schurkey! Thanks for your advice. I ordered the Actron CP7838, and that includes a recommended adaptor. Hopefully that will work. I'm trying to keep expenses down, so before I spend a bunch on a scanner, I'll try the cheaper testing first. My time is cheap (I'm retired). If I can't find anything the monkey way, I'll spring for a scanner. I'm hoping to stay under $250, but I'll go higher ifs needed. I don't know anything about scanners, so without suggestions, I'm going to have to study on them. I'm following a Snap-On Solus Pro on ebay, but I don't think that's going to work out.

Thanks PlayingWithTBI! I appreciate the tip.

 

[Hoot Gibson]

I checked the CTS, and it seems to be working. 3.2 K ohms cold (local temp is 78F) then I ran it for a few minutes, on dash temp gauge came up from the bottom, 440 ohms. According to a list I found in another thread, I think it's working.

Supposed to get the fuel tester tomorrow or Sat. After that, I'll start looking for a scanner. I just want to make it run!

Found out I have a scanner! Unfortunately, it's a New Generation Star Tester, for Fords and Mazda. No help. Anybody want to trade? I have factory manuals for the 1998 Lincoln Mark VIII. That was a painful endeavor.

 

[81nascar]

For fuel pressure an easy way is to make a t -type fitting at the fuel filter. It's much easier than trying to hook up behind the throttle body. The TBI doesn't have a schrader valve. Solus pro would work if you have the obd 1 attatchments . My prospects from what you describe I would lead to CTS sensor or clogged/dirty/failing IAC... Maybe fuel pump, but the fact that you can keep it running with your foot in it would lead me to think it's ok. Still never hurts to check.

 

[Sabinoerc]

I'm hoping to stay under $250, but I'll go higher ifs needed. I don't know anything about scanners, so without suggestions, I'm going to have to study on them.

If you are capable with laptop check out TunerPro. Freeware/donate + about $75 for a cable.
as others have said, many things could be cause. Fuel pressure is always at top of my list for something like this. I think important to verify it’s ok before chasing after other things.

 

[PlayingWithTBI]

It's much easier than trying to hook up behind the throttle body.

It is a little more work but, with an AFPR and a gauge, you can get it dialed in plus, it's easy to verify whenever you want.

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Here's when I was running a 28LB spring on my 5.7L

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[Hoot Gibson]

I'm baaacck!

Finally got the water heater replaced, and the sewer line cleaned out, and it quit raining for a few hours, so I got time to check my fuel pressure. I installed the adaptor between the fuel filter and the TBI.

Nothing. Zero reading.No pressure on the gauge. Not when I turned the key on, not when I got it running (bumping the throttle to keep it running), not when I turned it off. Never left zero.

The pressure gauge has a pressure relief button and hose, so I depressed the button while the engine was running, and gas ran through the relief tube, but it didn't seem like it was under much pressure. After I disconnected the pressure gauge, I hooked it to compressed air, and got a reading, so I think the gauge is working.

I checked the fuel pump fuse on the passenger side firewall, and the wiring connections for corrosion, so what's my next best move before I replace the pump? Fuel Pump relay? Or is the pump the most likely problem?

Thanks!

 

[PlayingWithTBI]

Not when I turned the key on, not when I got it running (bumping the throttle to keep it running), not when I turned it off. Never left zero.

When you turn the key on, engine off, the PCM should run the fuel pump for 2 seconds. Do you hear it running? It's hard to believe the fuel pump isn't running or your engine wouldn't at all. Once you get the engine running, shine a flashlight behind the injectors to see if you're getting an even cone of spray.

Everything points to a bad fuel pump or connecting hose inside the tank or even a plugged fuel filter (if your gauge is Teed in downstream of it. If you do replace the fuel pump get an ACDELCO EP381 from a 96 Vortec. It gives you more fuel rated at higher pressures and, since the FPR on the TBI controls it, it'll work fine in your application.

 

[Hoot Gibson]

Hey Peter,
I'm doing this on my own, so I can't listen and turn the key, or check the injectors when it's running. The pressure gauge is 0-100, so maybe it's got a couple of pounds but doesn't show it.

Key on, engine off, no pressure reading. I put the gauge in between the filter and the TBI. I changed the fuel filter when I started this, and it made no difference, so I'm assuming it's good.

Looks like the pump and/or the hoses is my best bet. I didn't want to drop the tank, but it seems I can't avoid it. Maybe I can figure out why the gas gauge is pegged past full when I get the tank out.

Thanks much for the recommendation for the pump!

 

[Schurkey]

The pressure gauge is 0-100, so maybe it's got a couple of pounds but doesn't show it.

I had an ancient--and inaccurate--fuel pressure gauge. I just bought a 0--30 gauge head for it to replace the 0-100 gauge that's failing. That'll be my TBI fuel pressure tester now.

Almost nobody verifies their pressure-gauge test equipment--fuel pressure testers, compression testers, etc.

Looks like the pump and/or the hoses is my best bet. I didn't want to drop the tank, but it seems I can't avoid it. Maybe I can figure out why the gas gauge is pegged past full when I get the tank out.

I would verify voltage at the fuel pump power wire, as close to the fuel pump as practical. This is typically at the rearmost harness connector before the harness goes up 'n' over the tank. Verify voltage with the pump RUNNING and the alternator charging.

Also look for voltage on the ground wire for the pump.

GM uses under-size wire for the fuel pump, so it's common to have some voltage drop on the supply side, and perhaps one volt on the ground side.

If the gas gauge is pegged past Full, the wire harness is probably broken somewhere between the gauge and the sending unit in the tank. On my '88, it was along the frame about under the driver's footwell area. I had to splice in several feet of wire because the original wire had corroded and then broken.