Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
It sure sounds like you have a charging problem. Have you measured the volt level at the battery when the vehicle does not start? If so, what was the voltage that you found?
No, I haven't measured the volt level of the battery yet. But, there is not a problem starting it numerous times after I either jump it or charge the battery.
If I use it every day it there is not a problem starting it. The only time it won't start is if it hasn't been used for a few days.
If that is the case, you may have an "extra" drain on the battery - or something that is not turning off when it should. There are a lot of control modules in the vehicles that are supposed to shut down after about 20-30 minutes and not drain the power from the battery. Or you could have some other piece of equipment (cell phone charger, power amplifier for the audio system, etc.) that is drawing just enough power to drain the system a little too quickly.
Let me send you this procedure that can be used to find out of there is any extra drain on the battery that should not be there. It will take some time to do this, and will require a little bit of equipment, but none of it is too expensive.
Battery / Parasitic Drain Test
Basically you will be looking for any "excessive" current being drawn from the battery after the 20-30 minute delay time. If you find something over about 25-30 milliamps, it would be a matter of pulling out fuses and disconnecting devices until you find what is drawing the power.
Please let me know what you find or if you need more help.
Take Care, Greg A.
The battery read 12.4 volts last night after cranking over the engine several times . But, the engine didn't start. This morning it it also read 12.4 and 12.5. And also wouldn't start.
As I stated earlier when I pour gas directly down the throat of the air horn it will start and run until I quit pouring gas down it.
I'm thinking there is a module or relay or ?, in the fuel system that is going out. It actually started doing this slowly, gradually worsening until now when it takes a boost to energize something in the fuel system to finally activate.
It could be the fuel pump relay. Perhaps there is some corrosion in the socket that it sits in and that is dropping the voltage to the relay enough to make it not work. Have you tried looking under that relay for any signs of dirt or corrosion? Can you hear the fuel pump when the vehicle will not start?
If you can tell me the engine size, I can probably get you a diagram of its location (in the underhood electrical center).
As I stated earlier the fuel pump is new and checks out ok according to the Haynes Repair Manual. I'm thinking it's further down the line. The engine size is in question, the book gives sizes for (the eighth charater of the vin. number ) V,U,T,W only. Mine is an
'R'.It is an 8 cylinder and rather peppy.
That's a 5.7L (see below).
I am not so concerned about the fuel pump itself, but the connections that supply power to the pump (which is through the relay and the wiring to the pump).
Very often it is recommended that the connector and wiring at the connector be replaced when the fuel pump is replaced. This is because sometimes the connectors heat up and start to melt and the wiring becomes loose. That is why I mentioned checking the relay (see below) and asking if you could hear the fuel pump when there is the no start condition.
Now that you have reminded me about the fuel pump connector issues, what I would like to do is actually check the voltage at the fuel pump connector wires to see if any power is getting lost along the way. But that can be kind of difficult (needs to be on a lift), so you might want to check that relay first. If at all possible, try to check the voltage at the fuel pump connector pins when trying to start. It should be right up to the same level as battery voltage. If you are loosing half a volt or more, you may not be getting the pressure you need to start up.
Please let me know what you find.
I replaced the fuel pump relay and cleaned the connectors. It still would not start with
12.4 volts at the battery. I put my battery charger on it set to boost and it started right up.The battery read 13.8 while running(apx.30 seconds till I shut it off.). The reading stayed at 12.4 after I shut it off. I then proceeded to start the engine over and over again( apx 10 times ) over the next 20 minutes all the while the battery read 12.4 and 12.3. however this morning while the battery was at 12.4 it would not start.
What I really would be concerned about is the voltage at the fuel pump connector itself. That is where the lose would be if there was any damage to that connector.
I am also going to send a note to a couple of other experts here I know and ask for their input. I will let you know when I hear back from them.
Here are a few comments I received:
BGHow about the fuel pump ground and the terminals for the fuel pump relay? Security?
MLSounds like it could be both Starter & Battery.Battery weak, goes to crank, Voltage drops to far = No Start
CHMy main concern would be if this engine has the proper fuel pressure. They stated that is will start if they pour fuel down the TB. These engines are real picky on fuel pressure and if they are not getting the 55 psi mark it will certainly not start nor run correctly until the 60 psi mark. I did not see any mention of any pressure tests at any point. Just something to think of.
Being a troubleshooting type of person, I like the last comment the most. If you have a pressure gauge, I would check the pressure with the key on and the engine off. According to the specs, it should be 60-66 psi.
I would do that both in the no-start condition (let it sit for a while), and then measure it once you connect the charger and boost it up. What I would be looking for would be a difference in the readings.
Please let me know what you find. This one is turning out to be a real head-scratcher!
One more comment:
I would start with reading the voltage at the battery when it is being cranked,if it going below 9v it will cause starting problems.I would also do a voltage drop test at the pump positive and ground connections,or try starting the truck with jumper wires directly from the battery as a test.
the voltage at the battery reads 9.8 volts while being cranked over.
the fuel pump pressure reads 62 lbs. when I turn the key on and then again when I turn
the key off. The fuel pump hums for the usual two seconds then shuts off , as soon as it shuts off the pressure drops to zero until I turn the key off or on again. It may be leaking from the guage connection, but I'm surprised it doesn't kick back on by it's self to keep the pressure up.
the engine will no longer start even with the charger attached and on boost.
because I work out of town I will not be able to check it out until next weekend.
That sounds like good pressure, but I don't think it should drop down to zero so fast. You might want to check and make sure that gauge is not leaking.
That pressure should hold even after the key is turned off, unless I am thinking of another vehicle. I will check on that to be sure.
The 9.8 volts sounds like a pretty deep drop in voltage, but it may be OK if it is just momentary and it comes back up to around 12.6 volts. If not, that battery may not have a whole lot of reserve capacity. It is amps you need during cranking, and the battery should be recharged during normal operation. So if the charger was not left on overnight (in slow charge), then that might be the reason for that. All of this cranking could have drained it. You might be able to leave the charger on boost for a short while and be able to try again today, but otherwise just leave it on slow charge for the long haul until we get this resolved.
I also want to let you know that the system here at Just Answer may send out occasional reminders to come back and visit this page. So if you get a "nag" message (reminder), just come back when it is convenient.
I have a few PDF files that you might want to look at during the week.
Fuel Supply Components Description
Fuel Metering Components Description
Fuel System Diagnosis
I appreciate your help and information and gave positive feed back.
However my Tahoe still does not run.. Once again it has morphed into into a different direction. Where as it used to start when boosted by my battery charger set to 50 amp boost, now it will not. It will turn over nicely ( without the battery charger ) and act like it wants to "catch" but usually does not. once in a great while it will start but will only run for a few seconds before dieing, acting like it is running out of gas. I also did check to make sure that it wasn't on 'empty'
To recap it has:
1) a new battery reading 12.9 to 13 volts then dipping down to 10.7 when turning over the starter.
2) a new fuel pump with 62 lbs. when the key is turned on and off and 55lbs. while running for its few seconds. it also holds its pressure for long periods.
3) a new fuel pump relay
4) a new fuel filter
I've read through the files you sent but they don't seem to point to the problem.
If possible can we start a new contract to pick your brain for further possibilities?
perhaps in a different direction than other than fuel , maybe timing or??????
Sorry for the delayed response, as I have been pretty busy over the last few days.
I am going to try and get you some help with this as I will be pretty busy for the next few days with another project. If necessary, I believe I can get the accept transferred to another expert that helps you. I just want to get you fixed up and running.
Thank you for your patience, Greg A.
Hi Gary, it's not a problem time wise.
I really apprieciate any help you can give me. This thing is becoming an obsession with me. I've been wrenching for 50 years and I refuse to let this beat me, it does how ever make me long for the days of a "Stromberg 97" setting on top of a flathead Ford.
Thank You ,George
Just checking in again to let you know that I will not be able to look into this until after noon (pacific time) tomorrow.
Thanks again for your patience.
I'm back for this afternoon & evening.
I agree that maybe we should go in another direction with this. Maybe having something to do with ignition or some other input to the computer that is keeping it from running properly.
So I was wondering if you have or know someone that has a code scanner or scan tool you can borrow. I know some auto parts stores will "lend out" scan tools with a small deposit so that they will be returned.
Also, most parts stores carry "Noid lights" which will help confirm that the fuel injectors are firing properly. You may even be able to borrow these from a parts store.
Please let me know if you can get some of these tools.
I have used a code scanner already and no faults were reported. Is a code scanner and scan tool the same thing?
I'll look into the niod light.
I was just wondering if you have a code reader, that you own, that you can use when there are problems. Sometimes codes are set that do not light up the check engine light the first time a problem occurs, but the "pending codes" can still be read with the tool.
Also, there are several flavors of scan tools. From simple readers to the once that can be connected to display what is happening in real time. Of course the more advanced ones are pretty expensive (running in to hundreds or thousands of dollars), and I wouldn't expect you to have one of those.
It sounds like you have good pressure from the fuel pump, so the next step, at least for fuel delivery, would be to check the injectors. That's why I suggested the noid light.
But I also received the following from one of the other experts here, and I thought I would pass it along:
Are we getting side tracked with the fuel in the intake? By that I mean, do we have a weak coil? Bad cap and rotor?
With these modern "computer controlled" engines, one weak link is all it take to keep them from running right.
I will also be sending notes to a couple of other experts here to have a look at this message thread and see if they have any input, as I might have missed something.
yes I own a code reader , I have put it on several times and each time it came up negitive for any problems.
The coil or distributer sounds interesting I'll go out and explore them now.
I checked for loose terminals and connections and came up empty. I haven't found any other test equipment yet.
when I turn it over and it runs for a few seconds ,it runs smooth but will stall immedienty if I give it any gas at all. It will also die on its own if left alone after several seconds( 5-7 seconds )
This brings to mind a 1977 Ford pick up I had with the 'new elecronic ignition system,' that would quit running every 50,000 miles due to the ' Control Module ' going out. They called it "The Brain" back then and it would act like it was running out of gas and just rolled to a stop some times it might start up again some times not.
It was interesting how at 50K it would go out like clock work until the patent expired and they could sell after market units that would last forever.
Anyway, in retrospect this acts very much like that. Does this Chevy truck with 107K miles have a control module that could be going out that would cause all of these problems?
Sorry about the delay. I am starting to wonder now if you have more than one problem going on here.
When the engine runs for a few seconds (5-7 then dies), this makes me think it might be a security issue, or some signal that is not getting to the computer to tell it to keep running. Without checking my notes, I seem to recall that the "prime" signal is what turns on the fuel pump to get the engine started, and then it needs something else to tell it to keep running (keep the fuel pump relay energized). Again, I will half to check my notes on this particular engine & computer, but that is what is popping into my head.
I also have a few notes from the other experts to go through to see what they have to say. I will try to get back to you with that soon.
Here are a couple of other experts comments
I think there is more than one problem here. The two combining make the symptom appear but they both need to be fixed. I know the battery is new but..
Quote:Hi Greg,the voltage at the battery reads 9.8 volts while being cranked over.
This is no good. Either the starter has way too high draw, there is a bad connection or the battery is junk, my vote is battery junk if we are guessing.
Next Quote:the fuel pump pressure reads 62 lbs. when I turn the key on and then again when I turn the key off. The fuel pump hums for the usual two seconds then shuts off , as soon as it shuts off the pressure drops to zero until I turn the key off or on again also not good.
So let's put the two together, fuel pressure drops off to zero meaning it is going to take more than the usual prime to get it going. Battery drops off means slower crank and less voltage to the pump which results in lower volume in a case when you need max volume. The two systems need to have a thorough going over. Fuel system isolated to find the leak and battery/starting system isolated as to what is causing the voltage to drop to 9.8 under load. I was guessing battery because it starts with a battery charger, that charger is not putting out the amperage that the battery should be capable of but without a starter draw test that is just an educated guess.
SK:This question goes all over the place!
I think I want to find out where we are at too.
I was under the impression that a few weeks ago that the vehicle would start and run, once it got started, for a whole day, and then not start the next morning.
Now it seems that it will start briefly (5-7 seconds), but then dies.
I also wanted to send the following PDF file along for you to look at. It shows how to troubleshoot the fuel pump electrical circuit. It also shows the my memory has not totally failed, as it has the part about the computer keeping the fuel pump relay energized if it receives pulses from the ignition system, while the engine is running.
Fuel Electrical Circuit Diagnosis
I sure wish I was there or could connect a GM class 2 scan tool to it can see what was happening.
I finally gave up and had the Tahoe towed to a garage. The owner told me he put the intake housing - duct back on the air horn and it worked fine. He hooked it up to his computer scan machine and it also read fine. Apearently the whole intake system must be connected for it to run.
We suspect that the original problem was corrected somewhere along the line, but with out the ducting connected I never knew it.
In all my years I've heard of such a thing, the first thing you do is remove the air cleaner so you can see all the parts and connections. I even re read the book ( fuel and elect.)and it didn't mention having it attached.
I still don't know what the original problem was , reading back .the only thing I changed was the fuel pump relay and I still had problems after that.
Thanks for all your help , George
Thanks for getting back to me & letting me know what happened.
Yep - these 'new fangled' engines with sensors all over the place gotta have everything just right to keep them running.
Please let us know if you have more questions in the future.