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TBI/EFI folks ever noticed this?

dyeager535

dyeager535

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Anecdotal, no real info to come of this unless it happens to you, but gave me a bit of a scare the other night. Others here ever noticed similar? If I hear or see something "wrong" with my vehicle (other than aesthetics lol), I want it fixed. I don't like failures on trips, so things like this bug me when they happen.

In any case, weather was cool, and needed to move the truck into the garage. So I fired it up, immediately coasted forward to the garage, then ran it for maybe a minute while I positioned it. Noted the oil pressure was 45 (normal for this engine) before I shut it down.

As soon as I shut it down, I heard the fuel pump whining. Unless the relay or oil pressure switch is stuck, that shouldn't happen. But it shut off after sounding like it built pressure up, which generally shouldn't happen with a sticky relay or switch. Possible, but not likely.

Worried about a potential random battery draining electrical load, I started with the google searches.

Finding nothing that addressed this particular type of event, engaged some folks that are familiar with this vintage injection, and just so happened to find two others that had it happen too...apparently under the right conditions (cold oil, colder ambient temps) the oil pressure can stay high enough for a bit after shutdown, to keep the oil pressure switch closed. I kind of wondered when it happened, but finding others that have had the same experience, I'm pretty comfortable not worrying about it being a random event.
 
I have not noticed my in-tank TBI pumps running after engine shut off. My truck is loud enough to not hear it possibly. Like you said...it may not be anything to worry about as long as the pumps do not run for more than a second after engine shut off.
 
1-ton said:
I have not noticed my in-tank TBI pumps running after engine shut off. My truck is loud enough to not hear it possibly. Like you said...it may not be anything to worry about as long as the pumps do not run for more than a second after engine shut off.
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It was actually significant. About as long as the prime cycle, which is why I questioned what was going on, like the key had been turned to "on". I'd say 3-4 seconds. Not a ridiculous length of time, but longer than I would have thought!

For some reason this pump is significantly quieter than the one it replaced (both Delco's, both worked fine it seems), I want to think I've heard this happen before, but just attributed the noise to something else.
 
I happens all of the time with cold oil, and a decent engine. But I will say that I can't hear it in my '95.
As long as it shuts off in a few seconds, your good.
 
My TBI swapped 79 does that as well. It has been years since I've driven anything with TBI so I figured it was normal.

Interesting related thought, but with a cold start it takes quite a while cranking before it starts, but after that, it will fire up immediately. I figured it was my oil pressure switch, but don't care enough at this point to worry about it, as it's getting parked out back for winter, and a 454 stroker swap next spring(hopefully, if all goes to plan).
 
Why does it run with the key turned off?

Only thing stuck in my head is that it's wired to constant you have a "slow to close" injector.
LMAO, cause I know nothing about this stuff. Mine shuts off with the key, but it's never cold here.
 
Only time the pump runs "temporarily" under normal operation is the prime circuit. Key to run, no distributor signal, no prime cycle in the past ~15 seconds, the ECM runs the pump for a few seconds to make sure there is pressure in the lines so the engine fires quickly.

Outside of that, need the signal that the distributor is turning, and/or oil pressure switch closed, to run the pump.
 
Yep, that's normal. When it is really cold, the pump will run a long time before oil pressure bleeds back off. Never noticed it on anything but tbi stuff
 
79rustyk10 said:
Interesting related thought, but with a cold start it takes quite a while cranking before it starts, but after that, it will fire up immediately. I figured it was my oil pressure switch, but don't care enough at this point to worry about it, as it's getting parked out back for winter, and a 454 stroker swap next spring(hopefully, if all goes to plan).
Click to expand...

When it comes to cold start on my TBI engine I engage the starter motor for about 2-seconds, and then wait for about 5-seconds for the shot of fuel my TBI just sprayed to run down into the cylinders. Then, I engage the starter motor again for about 1-second and it starts.
 
How cold? I've never noticed my burb do that.

Could be cause if it's cold outside, like below 10, I always let my stuff run for 3 or 4 minutes
 
Mine has never done that, but I removed the oil pressure switch and it never gets very cold here. So maybe confirms your idea of what’s going on.
 
bp71k5 said:
Mine has never done that, but I removed the oil pressure switch and it never gets very cold here. So maybe confirms your idea of what’s going on.
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The oil pressure switch in my TBI system doubles as a gauge sender and an ECM sensor in my 1991 V3500 Silverado with full gauges.
 
1-ton said:
The oil pressure switch in my TBI system doubles as a gauge sender and an ECM sensor in my 1991 V3500 Silverado with full gauges.
Click to expand...

I converted mine over to that style too. Still need to finish that write up, but those terminals get complex and hard to find thebpart numbers of what I used, vs what I bought to try. It and a three wire cts/sender save a fair bit of space and complexity imo.
 
1-ton said:
When it comes to cold start on my TBI engine I engage the starter motor for about 2-seconds, and then wait for about 5-seconds for the shot of fuel my TBI just sprayed to run down into the cylinders. Then, I engage the starter motor again for about 1-second and it starts.
Click to expand...
I do the same.
 
1-ton said:
When it comes to cold start on my TBI engine I engage the starter motor for about 2-seconds, and then wait for about 5-seconds for the shot of fuel my TBI just sprayed to run down into the cylinders. Then, I engage the starter motor again for about 1-second and it starts.
Click to expand...

imiceman44 said:
I do the same.
Click to expand...
But you guys live in warm areas..
I gotta ask if you have ever been in single digit temperatures?
I crank on mone until the oil pressure switch turns on and it fires. Then let it idle.
And I have heard the fuel pump relay hang on for a second or so in 40* temps.
 
6872xtc said:
But you guys live in warm areas..
I gotta ask if you have ever been in single digit temperatures?
I crank on mone until the oil pressure switch turns on and it fires. Then let it idle.
And I have heard the fuel pump relay hang on for a second or so in 40* temps.
Click to expand...

I a cold climate you probably have to do my technique times X2.
 
1-ton said:
I a cold climate you probably have to do my technique times X2.
Click to expand...
Nope! Hit the key, crank it a few, let it idle from there. I feel that it saves on the starter and battery, by not having to get the crank turning from a dead stop more than once. It takes more amps to get it turning than to keep it going.
This morning it was only 28*, just crank it and it runs.
 
Not tbi but when I did my fitech, my pump woul run for 20-30 seconds after the key was off. This was before it was running. I had an insufficient ground. Once I added a ground strap to the efi body it stopped doing that and started first turn.
 
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