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chevy vortex hard starting


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toolman0007
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Aug 18, 2012, 8:50 PM

Post #1 of 46 (1755 views)
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 I have an 2001 Chevy express 350 vortex motor. only way it will start is by putting the gas peddle to the floor. once it starts the idle stumbles a bit but smooths out and will run high for about 3 sec. then drops to normal and as well I get a bit of well not black but gray smoke out the exhaust. check engine lite came on a week ago in reference to mass air flow censer tested that. 13.75 volts feed to it 4.30 volts on the signal side and drops when gas is pushed, as well as unplugging it when running there is a change in the way it runs. was told signal side should read 5 volts . I even tried tapping on it and there is no change. am i right to think the mass air flow is working ??. I was kinda leaning towards idle control valve. but readings there are where the should be. with it out and wired and the key on it dose retract the plunger fully. But thought it was suppose to extend fully in stead. any one with info it would be helpful. throwing parts at is not how I do things


Hammer Time
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Aug 18, 2012, 9:12 PM

Post #2 of 46 (1735 views)
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Is the check engine light coming on when you're not unplugging things?




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
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Aug 18, 2012, 9:55 PM

Post #3 of 46 (1721 views)
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The mass air flow sensor on that design generates a digital frequency signal, so the PCM can calculate air flow. You can't see this signal with a digital volt meter because the meter is going to average out the voltage. The PCM sends 5 volts on the signal wire to the MAF. The MAF pulses this 5 volt signal to ground depending on how much air is flowing through the sensor. You can measure the frequency with a meter that has that function, but it is almost near impossible to catch glitches because the signal is extremely fast (Khz). You really need an oscilloscope to check out a MAF properly if you know that power supply (battery voltage), signal voltage (5 volts), and ground (0.1 volt drop) is good to the MAF.

If you have a scan tool with datastream capabilities, you can look at the calculation the PCM figures out. It is usually in grams/sec. Sometimes you can also view the MAF frequency in the datastream also.

When you shut the truck off the IAC will fully extend and then retract a bit, to help in starting the engine. You don't want to test a idle air control valve that is removed using the PCM because more than likely the PCM will fully extend the pintle when you turn the key off causing the pintle to launch out of the motor. Once it does that you have to replace it. Best way to test an idle air control valve function is by using a scan tool with the idle control rpm function.

If you put the gas pedal to the floor during cranking, the PCM goes into clear flood mode. The PCM doesn't fire the injector in clear flood mode. The purpose of clear flood is to clear out a flooded engine. If you have to put it into clear flood mode to get it to start, you have a flooded engine. Could be a leaking fuel pressure regulator or some type of fuel leak underneath the intake. Probably wouldn't be a bad idea to test fuel pressure leak down rate.





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(This post was edited by Discretesignals on Aug 18, 2012, 10:16 PM)


toolman0007
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Aug 18, 2012, 11:33 PM

Post #4 of 46 (1702 views)
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no the check engine lite has not come on again since the first time. and it's been driven almost 200 miles


toolman0007
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Aug 19, 2012, 12:01 AM

Post #5 of 46 (1698 views)
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thanks.. I know about the two types of censers. mine is just a three wire connection and from my understanding it's a voltage type. given the fact it should have 5 volts at the signal wire i think I would not even get the 4.30 reading if it were a frequency type. my concern is it's only got 4.30 volts reading in stead of 5.0. how much dose that difference effect things as far as starting. as fore the IAC it dose fully extend when the key is turned off but retracts all the way in about 1/2 a sec after not part way. as far as clear flood mode I know I have good pressure just replaced the fuel pump almost two months ago do to the fact it quite working. but feel I will test that again just to get that out of the way. I do know it's either an air or fuel issue. have known others who tested their maf's thought nothing was wrong but after time replaced them only to find they were faulty


Discretesignals
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Aug 19, 2012, 12:43 AM

Post #6 of 46 (1688 views)
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The sensor is the voltage type, but it produces a digital signal. 5 V on and 0 V off. The frequency of that signal is what the PCM wants to see. The average voltage your seeing on your meter is going to change a little because the frequency of the signal is changing. You can't tell if the MAF is working properly by watching the average voltage your meter is displaying. You need something fast like a lab scope to see the signal properly. Even when viewing the voltage with the lab scope you can't catch glitching. You need to monitor the signal's frequency.

It's not a like a Ford sensor where the MAF produces a 0-5 volt analog signal.

Here is a great video..check it out:

http://www.youtube.com/watch?v=h5KAHv47viw





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Aug 19, 2012, 12:53 AM)


toolman0007
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Aug 19, 2012, 9:27 AM

Post #7 of 46 (1661 views)
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hey thanks for the link to the video. never ending process of learning. well I have to see if my scan tool can help with further testing. cen-tech can obdII code reader eobd scanner. if not it's either another tool or take it and have it tested. cause this thing is eating more fuel than it should and im not buying parts till I know for sure whats up.


Discretesignals
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Aug 19, 2012, 9:38 AM

Post #8 of 46 (1657 views)
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Quote
cause this thing is eating more fuel than it should and im not buying parts till I know for sure whats up.


Spoken like a true tech. Smile





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Hammer Time
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Aug 19, 2012, 10:07 AM

Post #9 of 46 (1653 views)
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I would take a hard look at the fuel pressure and especially the rest pressure. I know you didn't mention it but i suspect this thing is setting rich codes. They are known for leaking regulators.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



toolman0007
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Aug 19, 2012, 9:01 PM

Post #10 of 46 (1630 views)
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well did not have time today to get to my truck. if i'm not mistaken the fuel regulator is under the top portion of the plenum. if it's leaking where would the fuel be going. in the cylinders or is it possible to get in to the oil through the lower half of the plenum. any ways I will be checking the fuel pressure. if this gets solved I will surly let you know what it was. have a local friend that has a scope and will retest maf as well may be a few days but that's how life is. once the chevy is done I will get to my ford. check engine light's been on for a while now both banks running lean. don't drive it much but the way I see it better lean than rich


toolman0007
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Aug 19, 2012, 9:05 PM

Post #11 of 46 (1626 views)
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oh and no check engine is off and has not come on for over 200 miles. no pending or stored codes are coming up


Tom Greenleaf
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Aug 20, 2012, 8:38 AM

Post #12 of 46 (1612 views)
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Just a comment: It's not better lean than rich it needs to stay in parameters or will waste fuel either way. Hammer mentioned fuel pressure holding. That is that it will maintain that pressure and not leak down if only returning to tank,

T
_________________________________________
Long retired now


Hammer Time
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Aug 20, 2012, 8:56 AM

Post #13 of 46 (1606 views)
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I'm still waiting for a fuel pressure reading and whether the pressure maintains when the key is shut off.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



toolman0007
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Aug 20, 2012, 8:04 PM

Post #14 of 46 (1585 views)
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sorry haven't got the chance to check it yet. have to take it to my friends place. that's a tool I don't have as soon as I know something I will post it


Tom Greenleaf
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Aug 21, 2012, 7:29 AM

Post #15 of 46 (1569 views)
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This one may only fit your Vortec fuel rail and some others without a bunch of adaptors for others.............



~ $45 bucks in stock in many places. The damage possible for improper fuel pressure and delivery will make that look like pocket change. Ask, but not sure if these can be loaned. Waiting may cost you a fortune,

T
_________________________________________
Long retired now


(This post was edited by Tom Greenleaf on Aug 21, 2012, 7:30 AM)


toolman0007
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Aug 21, 2012, 8:10 AM

Post #16 of 46 (1560 views)
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he hee yep like putting gold in the tank, have a buddy has had one for years he says he has only used it once. stopping by his place later today


Hammer Time
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Aug 21, 2012, 9:29 AM

Post #17 of 46 (1552 views)
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Quote
have a buddy has had one for years he says he has only used it once.


Then he isn't working on much late model stuff because it is the most used diagnostic tool on today's cars beside the scan tool.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Aug 21, 2012, 9:30 AM)


toolman0007
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Aug 21, 2012, 9:21 PM

Post #18 of 46 (1533 views)
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well now I know why he has not used it in so long. grate guy knows what he's doing but some times forgetful . anyways got a tester here's the stats ---
turn the key on it snaps right to 60 psi then drops to 55 psi . running it sets at 53 psi turn the key off it's at 48 psi . it took 2 min to go from 48 to 45 another five min and it was at 40 psi im thinking every thing is fine


Hammer Time
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Aug 21, 2012, 9:27 PM

Post #19 of 46 (1525 views)
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I'd be concerned where that pressure is going at rest. If it's leaking at the regulator, it will run to cylinders 3 and 5. From there it will either hydro lock or dilute the oil.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



toolman0007
User

Aug 21, 2012, 9:44 PM

Post #20 of 46 (1518 views)
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so what are you saying ... the resting pressure should remain at the start level and hold for a longer period .. no smell of fuel in the oil


Hammer Time
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Aug 21, 2012, 9:47 PM

Post #21 of 46 (1515 views)
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You lost 20PSI in 5 minutes. That should be no more than 5 or 6 PSI.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



toolman0007
User

Aug 21, 2012, 10:12 PM

Post #22 of 46 (1510 views)
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   so there is an issue there. it was just 6 weeks ago pulled in for gas and it stalled just rolling in to the station. filled it up and it would not start pump died. it's got a 14 foot by 8 foot box on it, went home got the generator grabbed the saw and cut a hole in the floor. new pump and filter. guess i'm going to have to go a bit further and get to the regulator. got 126000 on it plan on keeping it for a while. well thanks for the info and the help will let you know what I find. might be a few days though


Hammer Time
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Aug 21, 2012, 10:17 PM

Post #23 of 46 (1507 views)
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If you have a scan tool with data, clear the adaptive memory and then start it while monitoring the adaptives and see if they immediately start moving negative.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



toolman0007
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Aug 21, 2012, 11:35 PM

Post #24 of 46 (1503 views)
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   will do that first thing in the am


toolman0007
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Aug 22, 2012, 9:35 PM

Post #25 of 46 (1486 views)
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been a long day. and you will have to excuse me i'm still learning this scanner and what every thing means LOL ... the ect comes up -8 and a lot of the short term and long term fuel trims are in the neg as well shrtft1-10.2 longft1-1.6 shrtft2 -8.6 shrtftb1s1 -10.2shrtftb2s1 -8.6 . I also found that I can read the maf with a graph as well. it appears to me to be all over the place but dose spike when the gas is hit




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