1990 C4 Won't Start - Mechanics and I are stumped!
11-30-2014, 12:47 AM
#41
Team Owner
Pro Mechanic
Leesvet,
re-read your FSM. What you're saying is totally wrong. Pump runs when the engine is cranking.
Period.
re-read your FSM. What you're saying is totally wrong. Pump runs when the engine is cranking.
Period.
11-30-2014, 01:35 AM
#42
Team Owner
Pro Mechanic
F'k it... I will go ahead and waste my time, spoon feeding you the actual FACTS, as opposed to the massive cofusion that you have crated for yourself.
1. You honsetly believe in an EFI vehicle, the engineers are going to rely on the uncontrollable rate of leak down the fuel system has, to "meter" fuel during starting?? If you do...
Didn't you say elsewhere that "EFI is 100% about accuracy"?
2. If that were true (that line pressure was used to meter fuel during starting) why have a "Clear flood mode" built in? Wouldn't it clear eventually as line pressure drops??
3. What about extreme conditions? If it's extremely cold, and pressure is dropping as you crank...how's it going to get enough fuel to start (as just one example)?
But none of that^ matters b/c what you're typing is wrong anyway and now I'll destroy your misunderstanding of the "facts". Here we go...
You're not passing on fact, you're passing on misinformation, which confuses the unwitting...not helpful.
You are dead assed wrong. And here is where you go wrong:
probably a higher enough rpm to indicate the engine IS running
That is the crux of all your misguided thinking. Does it say "probably" in the FSM that you have? No it does not. Now it's FACT TME.
The ECM DOES run the pump for ~ 2 seconds at key on (and only Key On)...like you said, then turns it off, Until it gets the dist reference that its looking for.
When does that happen? As soon as you crank the engine! In FACT leesvet, that happens w/in 1/4 turn of the crank shaft, (with an L83 or L98 -1* of crank revolution in an LT1 or LT4) as the 8 pole reluctor wheel passes the pickup coil. As soon as the ECM sees ONE reference pulse from the pick up coil, which is 1//4 crank turn or less, pump goes on, and remains on as long as there is a reference pulse....which is as long as you continue cranking or the engine starts.
The entire problem with the foundation of your last several epic novel posts that are all wrong, is the ASSumption that you made...
#1: "probably". That the ECM reference pulse is "probably" when the engine is running. NO! It is when the first pulse comes from the distributor when cranking which is effectively, instantly (in less than 1/4 crank turn).
#2: That we turn the key from off to crank instantly. The FSM is referring to the 2 second on time for a KOEO situation. You turn the key to Run/On, but not to crank...pump runs for ~2 seconds. Engine is not turning, no reference pulse so pump turns off*. THAT is the ~2 seconds that the FSM is talking about. If we go from "Off" straight to "Crank", as we often do, then the "~2 seconds never happens. The key goes from "on" to "crank" in an instant, and the crank is turning, distributor sending a reference pulse to the ECM, long before the ~2 seconds is up...pump continues to run, based on the reference pulse from the already turning distributor.
*Back to ASSumptions. Here, you've assumed that the key is going straight from off to crank. You've also ASSumed the reason for the pump shutting off. It's not to prevent flooding as in this situation, the engine isn't cranking. There is simply no need to run the pump on, when the engine isn't turning...right? Right. That simple.
You're FSM is not wrong, but you're right...your comprehension needs help.
By "starts" the FSM means receives that reference signal from the distributor that you were talking about. That happens w/in...1/4 turn of the crank. So yes, key on, pump runs about 2 seconds, then shuts off as you said...until the ECM gets it's reference signal....1/4 turn of the crank.
Because you're making ASSumptions and guessing, that's why.
No, no, no. More ASSuming and guessing about how it really works. Again, is that "control"? No it is not. Pump running, steady pressure is control. That is how it works.
You are wrong. FSM is not wrong. You made up/added stuff to what the FSM actually says.
Easy...b/c it's not..."etched in stone". It's a slaughtering of the facts and simple operating principles. People who don't know, come here looking for GOOD advice (like the OP). You're info is WRONG...so that is why I correct (not debate) it.
i "get it"...but it won't work they way you've said b/c the system doesn't work they way that you claim that it does.
Not enough...apparently. You need to go back to fuel pump school.
Well...now you've gotten something right! Come with the real facts and there won't be any "debate". I wouldn't call this a debate; that involves opinion. In this case, you're just wrong. Fuel pump runs during cranking. You claim that you like to learn things....if you read this carefully, you just did. You asked me to prove it...tomorrow, I will, and you can learn some more.
.
1. You honsetly believe in an EFI vehicle, the engineers are going to rely on the uncontrollable rate of leak down the fuel system has, to "meter" fuel during starting?? If you do...
Didn't you say elsewhere that "EFI is 100% about accuracy"? 2. If that were true (that line pressure was used to meter fuel during starting) why have a "Clear flood mode" built in? Wouldn't it clear eventually as line pressure drops??
3. What about extreme conditions? If it's extremely cold, and pressure is dropping as you crank...how's it going to get enough fuel to start (as just one example)?
But none of that^ matters b/c what you're typing is wrong anyway and now I'll destroy your misunderstanding of the "facts". Here we go...
The ECM manages the pump on/off. Until it gets the dist reference that its looking for, probably a higher enough rpm to indicate the engine IS running under its OWN power and NOT the starter, it DOES NOT allow power to pass thru the FP relay. That's a fact Jack. After that initial 2 secs...its done. No mas.
probably a higher enough rpm to indicate the engine IS running
That is the crux of all your misguided thinking. Does it say "probably" in the FSM that you have? No it does not. Now it's FACT TME.
The ECM DOES run the pump for ~ 2 seconds at key on (and only Key On)...like you said, then turns it off, Until it gets the dist reference that its looking for.
When does that happen? As soon as you crank the engine! In FACT leesvet, that happens w/in 1/4 turn of the crank shaft, (with an L83 or L98 -1* of crank revolution in an LT1 or LT4) as the 8 pole reluctor wheel passes the pickup coil. As soon as the ECM sees ONE reference pulse from the pick up coil, which is 1//4 crank turn or less, pump goes on, and remains on as long as there is a reference pulse....which is as long as you continue cranking or the engine starts.
The entire problem with the foundation of your last several epic novel posts that are all wrong, is the ASSumption that you made...
#1: "probably". That the ECM reference pulse is "probably" when the engine is running. NO! It is when the first pulse comes from the distributor when cranking which is effectively, instantly (in less than 1/4 crank turn).
#2: That we turn the key from off to crank instantly. The FSM is referring to the 2 second on time for a KOEO situation. You turn the key to Run/On, but not to crank...pump runs for ~2 seconds. Engine is not turning, no reference pulse so pump turns off*. THAT is the ~2 seconds that the FSM is talking about. If we go from "Off" straight to "Crank", as we often do, then the "~2 seconds never happens. The key goes from "on" to "crank" in an instant, and the crank is turning, distributor sending a reference pulse to the ECM, long before the ~2 seconds is up...pump continues to run, based on the reference pulse from the already turning distributor.
*Back to ASSumptions. Here, you've assumed that the key is going straight from off to crank. You've also ASSumed the reason for the pump shutting off. It's not to prevent flooding as in this situation, the engine isn't cranking. There is simply no need to run the pump on, when the engine isn't turning...right? Right. That simple.
uhhh cause it might flood if it KEEPS on pumping fuel to an engine that's NOT firing and running yet>? hmmm. It has the fuel under pretension....that's plenty to start the engine. ALL it needs until it is running on its OWN and NOT the starter. THAT is built in. Go read the electrical section.
Well...now you've gotten something right! Come with the real facts and there won't be any "debate". I wouldn't call this a debate; that involves opinion. In this case, you're just wrong. Fuel pump runs during cranking. You claim that you like to learn things....if you read this carefully, you just did. You asked me to prove it...tomorrow, I will, and you can learn some more.
.
Last edited by Tom400CFI; 11-30-2014 at 01:58 AM.
11-30-2014, 11:01 AM
#45
Drifting
to all you guys with more stars than me.....I count on your expertise all the time....stop sounding like a bunch of morons.....you're disallusioning me....
11-30-2014, 11:27 PM
#46
Race Director
When my car did this I fixed it by doing a minimum idle adjustment:
http://forums.corvetteforum.com/1570563689-post1.html
http://forums.corvetteforum.com/1570563689-post1.html
12-01-2014, 04:41 PM
#47
Instructor
Member Since: Oct 2010
Location: Bayonne New Jersey
Posts: 169
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Thanks for the input, guys. Given my car is around the 80000 mile mark, the IAC valve seems to be suspect. I've ordered a replacement and hope to work on it this Saturday. These guys at the chevy dealership don't seem to really know what they're doing, and I'm going to get the car back to my place for the time being. If it's not the IAC valve I'll check the fuel filter. I really appreciate the suggestions!