Fuel Pump Relay issue...maybe?

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east302

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I’d agree, it doesn’t fit your symptoms that well if it quickly returns to normal starting. If it was the CTS, holding the gas down would still result in an extended crank time.
 
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doncaruana

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Still monitoring and the scenario is consistent thus far. Cold, starts right up. Warmed up and sits for a bit, hard start. Second try works.
 
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doncaruana

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Does cycling key on 2-3 times start easy every time? That usually means fuel pump problem(s).
I don't drive it enough to be able to say to be honest. And I'm ecstatic I got my daughter to do the first cycle!
 
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doncaruana

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So...the shop I took it to said the ECM is dropping the signal to the fuel pump. He showed me where he had his scan tool hooked up and monitored the signal and the fuel pump signal from the ECM drops out when I have the hard start issue.

Two things...one - I do trust this guy. Plus he showed me the graphs and everything. And he's not the kind would take me for a ride. Plus, they told me if that doesn't solve the problem, they will refund me.

But it goes back to being a little more baffling. The fuel pump/check valve hypothesis was very predictable. This not so much. And a little surprising that more wouldn't be failing.

I'll post back when I get it back and we find out if that was indeed the problem or not.

Incidentally...anyone know what is required for a new ECM? From reading it just has to be "programmed" to your VIN? Is that it?
 
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jc98ss

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Sorry i haven't responded until now, i need to fix my notifications in the settings....our tahoes are doing the exact same thing, and im almost certain it is the check valve in mine...the obd2 scanner i bought is bafx products bluetooth scanner, it's under $25 on amazon and has definitely helped me with pinpointing this issue.....i drove over 400 miles this past Saturday on a little road trip with no issues at all, several stops and leaving the tahoe running or restarting it after only being shut off for a couple minutes....no hard start issues, got to my brothers house, shut off for 45 minutes and then "start-die-start-run perfect" with a p1351 kicked after the start-die....it is very predictable and consistent.

So to further check the diagnosis outlined in post 26, i decided to perform a little test....i left work (perfect cold start) and drove to the gym (about 15 minutes, long enough to get fully up to operating temp)....i knew that when i came out of the gym (about an hour) i would get a start-die-start-run perfect with the code kicked.....so i decided to turn the key just enough to crank for about a half second.....just bump the starter....the idea was that if there was an air pocket in the fuel line created by a faulty check valve, i would in a sense prime the line by cycling the key just long enough to let the air get up through the injectors.....i did this about 7 or 8 times but never fully started the truck....after this, it cranked right up with no code....this tells me that the next step in confirming this issue would be to purchase or rent a fuel pressure tester and check bleed off after priming the pump...

sorry for the long drawn out post, hope this helps folks in the future who are trying to figure this out.....i will post results of pressure bleed off as soon as the tester i bought comes in.
 
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jc98ss

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I believe the reason the computer is dropping the signal to the fuel pump mentioned in post 35 is because the ignition is active but the rpm is under 250, kicking the P1351 code.....cutting the fuel pump means the computer is doing its job once symptoms for this code coming from the crankshaft position sensor are present....think about it, it cold starts and runs absolutely perfect all day.....i honestly would try a pressure test before replacing the ecm....BUT with that said, a 411 swap with an 01 express van flash isnt a bad idea in its own right....its actually a very simple re-pin and a huge upgrade for these trucks, opening a lot of doors for future mods if you plan to go that route.
 
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doncaruana

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I believe the reason the computer is dropping the signal to the fuel pump mentioned in post 35 is because the ignition is active but the rpm is under 250, kicking the P1351 code.....cutting the fuel pump means the computer is doing its job once symptoms for this code coming from the crankshaft position sensor are present....think about it, it cold starts and runs absolutely perfect all day.....i honestly would try a pressure test before replacing the ecm....BUT with that said, a 411 swap with an 01 express van flash isnt a bad idea in its own right....its actually a very simple re-pin and a huge upgrade for these trucks, opening a lot of doors for future mods if you plan to go that route.
Hmm. That's an interesting thought on the voltage drop out being still a symptom and not the disease and one I thought myself. No idea how valid that is. And, they pressure tested it and it was fine.

I'm not going to try any upgrades, I just want this programmed to my correct VIN and see where that leads us. My money right now is that it won't fix the problem. And then they'll owe me a big fat refund.

I just got a long drawn out email from the owner explaining away everything. And he says the supplier told him they put a "dummy program" in there. But I call BS because it's supposed to be an unprogrammed unit and they even say it needs to be programmed right on it. Never even bothered to do anything to offset the cost. Extremely disappointed. I can get it done tomorrow by someone I trust for $140 or wait until Wednesday and pay $260 (which I'm SURE is more money for the shop to be the middle man because they farm it out, all part of the novel they sent). Guess which one I'm opting for.
 

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doncaruana

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This is 1st link I clicked.
Yeah, the money grubbing owner that replied said this:
"While there is a possibility that we received a PCM that was previously installed and programmed on another vehicle, I don't think that it is this case. The reason being is when we talked to the company that programs the vehicles for us they were saying that the rebuilders don't ship these PCM's out blank and have a "dummy" program in it. I'm not sure of the reasoning behind that, but that would be why it was programmed to when we got it. I also don't think this was a junkyard unit because the supplier we used is a trustworthy and reputable company and to the best of our knowledge we have never received a part from them that has come from a junkyard."

I don't buy that for a second. Moreover, I don't think their 3rd party is actually charging them $260 to do programming - I'm sure he's getting a little on the top there. And that's the part he should be giving up because at this point it costs him nothing - no work, nothing. Just money for existing. Yeah...I'm pissed.
 
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