Starting and idling problems

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Boony405hp

Boony405hp

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I'm having issues with my 5.7 running and idling. I turn the key and I can hear the fuel pump prime, I push the start button and the engine fires, runs for a second or two then cough's and dies. I've just had the fuel injectors all professionally cleaned and serviced so I know they are in perfect order and there is fuel in the tank.
 
I think you will need to figure out if it's losing fuel pressure, or spark. Ima thinking it's fuel, so I'd be putting a pressure gauge on it.
It kinda sounds like the pump loses electrical power in the run position.
 
AJ/FormS said:
I think you will need to figure out if it's losing fuel pressure, or spark. Ima thinking it's fuel, so I'd be putting a pressure gauge on it.
It kinda sounds like the pump loses electrical power in the run position.
Click to expand...

I put a volt meter on the fuel pump connections and when it initially primes I get voltage and then then cranking and starting I get my 12volts and then when it dies I lose voltage. I don't have a pressure gauge but I'll have to buy one and install it in the line somewhere as it sounds like a good thing to be able to inspect when needed. The fact that it starts and then dies makes me think it might not be the fuel pump and perhaps an electrical issue? If it was just cranking then perhaps I'd suspect a dodgy fuel pump.
 
Wait up, you already proved my point, when you said; "and then when it dies I lose voltage." Would it be more correct to say;It doesn't die and then lose voltage; it loses voltage and then dies.
That's probably the ASD (Automatic Shut-Down) module.I can't say what it's responding to, unless it thinks the vehicle is being stolen (anti-theft program).The priming signal does not go through the module; it is a timed computer signal,activated every time the key is cycled.
Someone else smarter than me will be along shortly to help you. Hang in there. No need for a pressure gauge just yet.
In the meantime he will want to know what vehicle we're working on.
 
AJ/FormS said:
Wait up, you already proved my point, when you said; "and then when it dies I lose voltage." Would it be more correct to say;It doesn't die and then lose voltage; it loses voltage and then dies.
That's probably the ASD (Automatic Shut-Down) module.I can't say what it's responding to, unless it thinks the vehicle is being stolen (anti-theft program).The priming signal does not go through the module; it is a timed computer signal,activated every time the key is cycled.
Someone else smarter than me will be along shortly to help you. Hang in there. No need for a pressure gauge just yet.
In the meantime he will want to know what vehicle we're working on.
Click to expand...

It's in a Valiant Charger, it's a 5.7 hemi from a charger, 6spd manual with a flashed 05 ram computer and harness from hotwire auto. The car previously ran, but I was running it on a some 6.1 injectors but then I had the 5.7's professionally ultrasonic flushed and flow tested, and new caps and o-rings installed, so they are proven to be working.

So I turn the key in which it primes the fuel pump and you get 12V at the fuel pump terminals while this occurs, once it finishes priming the pump the voltage goes away until you crank it by pushing the start button. 12V is then present and remains while the car is running but then after a second or two the car just dies, whether the ASM module now has an issue? . It cranks and fires up everytime and then dies, if it was a faulty fuel pump or fuel issue i'd have thought it might have trouble starting occasionally or not fire at all but it fires as normal each time then dies. Did not have this issue before and don't remember changing anything.
 
I was thinking it sounded an awful lot like the anti-theft stuff as well. That will let the car start and run for a few seconds, but will shut it down shortly after. I would think the flashed computer would have taken care of that, but you might check with Hotwire and see if there is any troubleshooting they could help you with to confirm that. I'd double check all sensor connections as well. Could be starting up fine, but notices a sensor out and instead of doing a limp mode thing just kills it. Not sure how the factory computer handles all that as I went aftermarket.
 
I would put the 6.1 injectors back in and see if it solves your problem.
 
Here is factory mode of operation:

The following actions occur when the starter motor is engaged.
•If the PCM receives the camshaft position sensor and crankshaft position sensor signals, it energizes the Auto Shutdown (ASD) relay and fuel pump relay. If the PCM does not receive both signals within approximately one second, it will not energize the ASD relay and fuel pump relay. The ASD and fuel pump relays supply battery voltage to the fuel pump, fuel injectors, ignition coil, (EGR solenoid and PCV heater if equipped) and heated oxygen sensors

I would check it for codes , If either cam or crank is lost it will shut the ASD off.

I agree, if you weren't having any problems with the other injectors I would put them back in and see if it runs. Seems odd if that was the only thing changed and it caused this problem.

The vehicle theft will disable the engine after 2 seconds of operation and wont allow it to crank , should leave a trouble code if that was a problem. This shouldn't be a problem with your ECM though.
 
Good thought's and input lads. I was thinking along the same lines of re-trying the 6.1 injectors, and if it runs on that then it's got me buggered as to why the 5.7 ones wouldn't be working. It is a 6.1 fuel rail, wouldn't have thought that would be an issue though. If no luck, i'll report back with what I find out. It will probably have to wait till the weekend till I can get back to the car.
 
If you put the 6.1 injectors back in and it runs, then my first thought would be that the 6.1 injectors are bigger and giving it more gas and that's what it is needing.
The factory computer is going to give you a tune for a stock car, and that is assuming everything is correct as far as specs. You need to make sure that it is getting the proper fuel pressure, The sensors are giving proper signals. Coolant, Intake air temps are correct , map sensor etc.
For example, if your coolant temperature sensor signal is off 15 degrees telling the computer it is 70 when it actually 55 degrees, that may be just enough to lean it out and cause a starting problem.
Also these swaps are usually getting free flowing headers and exhaust systems that are going to change things.
When I talked to Hotwire they recommended a different tune over stock in these resto mod cars, he said they couldn't believe how much better they run and sound different with the updated tunes.
 
I guess it's possible one of the injectors has some kind of short that is pulling too much current and messing with the computer. It could see a really high draw and shut itself off as a means of protection. I'd think since you got them cleaned that they would have noticed, but if they just hook up a power supply to open them up then they might not be paying attention to how much current they are actually drawing.
 
I think post #8 says it all.
I had the same thing on an older Dak. It was the cam sync generator. The SFI computer needs to know where #1 piston is in it's cycle, to begin counting. If no sync.signal is found, it does not compute, and ASD will be engaged.
 
Update: I retried the starting with the rebuilt 5.7s after rebuild, struggled to start first go, then second go it fired and then died, if I give it some throttle it would keep running although felt a bit rough. Since I only have 5 X 6.1 injectors that I know flow I had to use 3 X 5.7s. Not ideal but has worked in the past. Sure enough it fired up and ran and idled without stalling.

So it's either a fuel pressure issue OR these 5.7s have something wrong with them.

What's the difference between the 5.7s and 6.1s pressure wise, I believe I've read 30lbs vs 34lbs? Would that be enough to cause a starting issue if pressure was an issue. So now I'd have to install a pressure gauge to check? Pity there isn't a screw on port like on some other factory fuel rails
 
5.7 injectors installed after cleaning and new o-rings and end caps (finally fires but then stalls)
[ame]https://youtu.be/e0bVj1DpofM[/ame]

Mixture of injectors (5 x6.1, 3x 5.7)
[ame]http://youtu.be/TLok8rwBJ6s[/ame]

How it ran originally on mixed injectors before cleaning
[ame]http://youtu.be/dTlruNZpMZQ[/ame]
 
I assume you have headers on it. One nice thing about that is if you let it run a little like in the first video you can quickly touch the header tubes and make sure they are all getting equally hot.
If you had one not getting hot that would indicate a problem in that cylinder. You could have an injector not flowing enough or even leaking down .
If you don't have complete confidence in these 5.7 injectors , it may be time to put new ones in it.
You could even get a hold of performance shop like Modern muscle and see if they would have a good set, I am sure they upgrade to bigger ones a lot and have good stock ones off a running vehicle.
 
That seems a lot like what happened to mine after a few miles. I have a fuel pressure gauge in my system so I could see it was a fuel pressure issue. What I thought was a pump that couldnt hold pressure was actually a bad fuel filter/regulator. It literally had 100 miles on it when it crapped out. Motor would idle poorly, with fuel pressure so low it didnt even register on the gauge. I was baffled at how it even ran.

Get a pressure gauge on there for sure, otherwise you're just chasing your tail.
 
I'm going to order an electric gauge and run a sender so I can permanently monitor it if needed.

Good news though, after doing numerous tests checking volt drop at the fuel pump etc thinking perhaps it was getting full voltage and therefore not pumping out at its optimum pressure. I found nothing out of the ordinary I thought, look, I'll swap the 5.7s back in again and see what happens , fully expecting nothing to have changed. Sure enough bam fires in to life beautifully! I don't know if there was an air lock or some issue when I had taken the injectors out and left it to sit for a week? But after running the 6.1s and then putting the 5.7s back in She now runs sweet as a nut. I am still going to get he permanently mounted fuel pressure gauge for the dash though so I can monitor and help diagnose in the future if anything odd occurs again.

Thanks to all those that chimed in with ideas and things to check
 
Well i jinxed myself and it's doing it again, starting and idling then it almost dies then the revs pick up again. Hmm back to the drawing board, the car always seems to me to be running rich, quite fumy. Car runs full exhaust and cats so I thought it wouldn't be so fumey. Back to the drawing board, maybe vacuum leak?
 
Fuel pressure is critical. Being a 05 PCM the pressure should be 58psi. When using other than stock injectors you will need to scale the injector. Being that you are using a 05 PCM a CMR tuner will be able to dial you right in with little problems. If you are attempting to start with it being flooded, hold the pedal to the floor and crank it up. Holding the gas pedal down cuts of the injector to clear the motor when flooded. Your description seems like a fuel pressure problem to me. good luck...
 
Ok so I have installed an electronic fuel pressure gauge. When you turn the key it primes the pump and reads 50psi, when the engine is running it's reading 58psi. Is this normal for the corvette filter/reg to prime only to 50psi initially?

What is an acceptable drop off in PSI if you were to prime the pump only and then watch the gauge over a few minutes?

Car is still starting a bit rough but then after a bit of spluttering etc for 10-15 seconds it sorts itself out and idles fine.
 
Think about a wiring issue. After swapping parts, it ran good for a while then started acting up again. Maybe a wiring connection in one of the plugs is sketchy?

My background is in Industrial Controls and more often than not I find wiring issues are responsible for erratic behavior.

Cley
 
Boony405hp said:
What is an acceptable drop off in PSI if you were to prime the pump only and then watch the gauge over a few minutes?

Car is still starting a bit rough but then after a bit of spluttering etc for 10-15 seconds it sorts itself out and idles fine.
Click to expand...

The factory test:
Install the fuel pressure gauge: Start the engine and allow the fuel system to reach maximum pressure. Turn the ignition off.
NOTE: Fuel specification is 407 KPa +/- 34 KPa (59 psi +/- 5 psi).

Monitor the fuel pressure gauge for a minimum of 5 minutes.

NOTE: The pressure should not fall below 241 KPa (35 psi)

If everything checks out good with your fuel system ,You may want to contact Hotwire harness and ask their Tech about your problem. The factory system requires a scan tool to perform Electronic Throttle Relearn for idle problems . Maybe it will require a modified tune to fix the problem.
 
I use an external regulator and the system doesn't hold pressure with the pump off. When I start cold I have a toggle switch to run the pump for a few seconds then turn the ignition on to run the pump for a moment then crank to fire it up. Usually turning the ignition on alone is enough, but if you have a modified system similar to mine then priming the system first is needed.
 
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