mdkswan

I have a tuned port on a chevy truck,which is CA smog legal.A little while ago it developed a hard start problem,and it's consistant whether hot or cold. it's taking sometimes three or more long cranks to get vehicle started.I checked everything i could think of from fuel pressure to noid lights to ohm meters,everything i've found in my books and on this board. I counld'nt find anything wrong and finally gave up and went to GM,but after having vehicle for two days, the two techs who worked on it and the service manager said they could'nt fix it and sent me packing. Any help would be greatly appreciated.Thanks Mike

chevymec

iTrader: (5)

Mine does the same, and I just crank it and go. Could be the fuel psi leaking back into the tank.

JeffW

check cold start injector, timing is critical too. fuel pressure regulator, fuel pump. fuel pressure.

sofakingdom

iTrader: (1)

Forget the timing. It won't cause a no-start or even a hard-start, if the car runs right after it finally starts.

The engine requires 3 magic ingredients to run: air/fuel mixture, spark, compression. All you have to do is figure out which one disappeared.

Odds are, it's not compression or spark. That doesn't go away during cranking and come back after "3 long cranks".

Most likely, you either have too much fuel during cranking, or not enough.

Shoot some starting fluid into the intake before cranking it, and see if that changes it either better or worse. If it gets better, you don't have enough fuel; if it gets worse, you have too much.

Too little fuel = low fuel pressure, failure of pump to prime, bad injectors

Too much fuel = bad injectors (leaky), bad CTS (open or high resistance, which makes the ECM see low ambient temp, which makes it feed too much)

This isn't brain surgery or anything, it's just a car. Not aot of mystery to it, really. Don't allow it to intimidate you, just reason it out, logic will lead you to the source of the problem. Random parts swapping, guessing, "codes", dealers, messing with the timing (typical newbie response to blame EVERYTHING on "timing", because they don't know what it even is let alone what it does) are all excellent ways to lighten your wallet without fixing the car.

Vader

MD,

Welcome Aboard!

I think he's on to something, even if it is just a long piece of furniture.

A few more details might help. What year was the TPI "donor" car? There are some subtle differences in the fuel systems that may make diagnosis a little different.

Was the entire setup from the same vehicle (ECM, sensors, EST, and all)?

Also, when you tested fuel pressure, what was it?

I'm going to guess that someone has already checked to make sure the pump is running when the key is first turned on, right?

A little data about the year of the TPI and ECM would help. You may have an incompatible pair of items, such a an early ECM with a later TPI (lacking a cold start injector), or a MAF system with a fixed TPS throttle body, etcetera.

mdkswan

The tpi is speed density.I got the harness and ecm from Street and performance.I'll have to check the intake number to find out what exact year it is,i got it from a friend.And the new vin on my sticker from B.A.R has it smogged as a 92 firebird.I've had it on for a couple of years and have had no major problems until now.It was to the dealer before this last episode,and they said it was the fuel pump.Which i changed(all gm parts)that i believe was about 5 months ago,and then recently this started.The techs said they checked everything from the fuel pump forward and could'nt find a problem with vehicle.but with a shot of starting fluid it starst right up with minimal cranking.I had went through the trouble shooting charts in my books for no start but could'nt find anything wrong.The gm guys even checked the fuel pump volumne and they said it ok.Thanks guys for all your responces to my question.I'm going through my books again to make sure i did'nt miss anything.The biggest bummer is that it cost me $88.00 and they told what i had already figured out.Thanks Mike

DENN_SHAH

iTrader: (1)

first thing, i would look at the data with a scanner, what's the temp readings on both the air & coolant sensors, are they close to the same after it sits over night? after a hot soak? do the temps they show seem to be right?
what's the TPS reading?
what's the battery voltage the ECM shows when cranking?
when was the last time you had the injectors flushed? were they done on the motor or were they removed & sent off?

Rob Wade

Sounds to me like your loosing fuel pressure when it sits. Either the pump check valve (shouldn't be since its a new GM pump) or the injectors leaking down. Do you get a puff of black smoke when you first fire it up? Does the fuel pressure hold for a while after you shut off the truck? It should hold pressure for a while. What year chevy truck and how did you mount the fuel pump?

anesthes

iTrader: (12)

No? You sure about that? Wanna swing by the shop later on, bring a 6 pack and I'll show you some stuff with the laptop.. We will try to crank at say.. 30 BTDC. See how well it starts..

anesthes

iTrader: (12)

Sounds to me like a vac leak at the runner gaskets. It will prolly run the nuts, maybe even better than when fixed with the speed density system. Thap sees more air and is like "oh yeah!".

I'd get it idling and start spraying down the plenum/runners with carb cleaner and see if your idle starts hunting.

I don't think it's a fuel problem at all. You can verify that with a gauge, but i'd find it hard to believe.

You can hook up a scanner, but unless you have a good idea of what the idle MAP values were prior to the problem, and can compensate for environmental differences, then you might not find much to help. You can probably simulate the starting fluid by altering the crank AFR in the prom too, but i'd suggest finding the real problem.

-- Joe

firebirdjosh

iTrader: (1)

I had the same exact problem and changing the fuel filter fixed it. It doesn't seem like that's the problem but if its not new might as well swap it, its only $6.

sofakingdom

iTrader: (1)

A vacuum leak won't cause a hard-start condition. It WILL cause a poor idle condition in many situations; but not a hard-start. A vacuum leak at startup does absolutely nothing, because there's no vacuum; so nothing leaks. For that matter, with a reasonably small vacuum leak, the S/D system has no problem at all supplying the correct amount of fuel, because it supplies fuel on the basis of vacuum (which is affected only slightly if at all by a typical leak), and RPM. Therefore a vacuum leak will NOT cause a hard-start, and not even too terribly bad of a run-like-poop problem. If the engine runs reasonably correctly after it starts, it's not a vacuum leak problem; so don't bother even allowing yourself to be confused about that.

Don't take a left turn into the weeds by straying from the lack of fuel diagnosis you have already made. Now that you've told us what you REALLY have, which makes a HUGE difference by the way, I'd almost be willing to bet money that you actually have 2 problems: the first is that your fuel pump doesn't prime when you turn the key on, and the second is that you have a leaky injector and/or a bad check valve in your fuel pump.

Listen to the pump, and see if you hear it prime when you first turn the key on. If it doesn't, then there's your problem right there. If it does, try priming it 2 or 3 times, then see if it cranks up. If it does, but then fails to start after it's been sitting for a few minutes, then you know you need injector service. NOT new injectors from the dealer.

More likely though, in the swap process, your wiring got left off or otherwise improperly installed somewhere, and your pump doesn't give its 2 second shot at key turn-on.

Personally I really don't give a rip what the guys at the dealership could or couldn't find, or what they did to test it, or what; and neither should you. Evidently they're idiots or lazy. What they did or didn't or could or couldn't do, doesn't change the basic fact of whatever is wrong with the car. Forget that they exist, use some logic on your own, and proceed directly to the cause of the problem .... without them.

As has been posted here by others, "The simplest explanation that fits all the facts is usually the right one". Don't lose sight of observed reality.

anesthes

iTrader: (12)

No, it will cause a hard start. The MAP won't correct a thing during cranking, thats what the crank AFR routines are for.

A vac leak also might not show up at all as a rough idle on a S/D system.

That is a possibility but I'd be surprised if the dealer didn't notice the pump not kicking on when key on. Still should be checked.

-- Joe

sofakingdom

iTrader: (1)

There's no vacuum during cranking. Or at best, VERY LITTLE vacuum. Therefore the ECM has nothing to correct for.

The cranking AFR routines involve primarily coolant temp and ambient (MAT) temp; not vacuum.

And of course, a vacuum leak that's big enough to affect cranking AFR so much that it will cause the car not to run, will be SO HUGE, that there's ABSOLUTELY NO WAY it wouldn't be noticeable once the engine is running.

And furthermore, a vacuum leak that's so serious as to produce the observed symptoms, won't just magically heal itself after "3 or more long cranks". The thing most likely to produce that synptom is a lack of prime routine, such that there is no fuel pressure until AFTER THE MOTOR HAS CRANKED LONG ENOUGH TO BUILD UP OIL PRESSURE. Which is of course the "simplest explanation that fits all the facts" (emphasis on "fits" and "all").

You're not doing him any favors by feeding him more "maybe it's this, maybe it's that" crap to go chase after, when he hasn't covered the "simplest explanation that fits all the facts" yet.

Stick to the basics.

Merlin

Is there an echo in here?

Data. We need data. Fuel pressure NUMBERS, not just "it was tested and is fine."

The pump primes, yes or no.

IROCThe5.7L

I'd get yourself a fuel pressure tester, and watch your pressure after the vehicle is turned off. If it drops off fast, then you can look at the injectors/regulator/check valve.

mdkswan

Thanks all for your replies.And yes the fuel pump does give a prime shot when key on. i have pressure set at 42 p.s.i. with hose off,there is a pressure gauge on fuel rail and i have a electronic gauge in cab,and i have'nt noticed any erratic readings while driving.My regulator is a Holley,which i don't know is good or bad after reading the reports on the board.I've had the rails off the intake to check for fuel leaks and didn't find any leaks.My injectors are about two years old and have'nt been serviced.Thanks Mike

anesthes

iTrader: (12)

Now that your finished performing tests that the newbie suggested, have you tried hunting for vac leaks? Still might not be the cause, but I've seen it more times that not on old TPI setups.

If you were a local guy i'd invite you to my shop to help you troubleshoot this. Oh well

-- Joe

sofakingdom

iTrader: (1)

1. A lower post count than someone else doesn't make one a "newbie" to working on and understanding cars. Nor does it affect the laws of physics; like, flow occurs from a higher pressure area to a lower pressure area, so if there's no pressure differential, no flow occurs (e.g. if there's no vacuum, such as there isn't any when the car isn't running yet, vacuum can't be leaking, so a vacuum leak is not an issue at that time).

2. Being recently appointed to Moderator status on one of the other boards may allow one certain privileges; however, alteration at will of the laws of physics is not granted at that level.

3. Which is of course not to say that there isn't a vaccum leak, since we all know how prone TPI is to developing those over the lifetime of the parts; only that the symptoms as described DO NOT indicate a vacuum leak, and that therefore, although checking for vacuum leaks in general might be worthwhile, it WILL NOT SOLVE the problem at hand, but rather will merely waste the guy's time.

4. Haven't heard yet about a fuel pressure leak-down check when the car is shut down. Which is of course, at the root of the problem. We also haven't heard yet if turning the key on, letting it prime, turning the key off and back on and letting it prime some more, 2 or 3 times, will make the car start up like it's supposed to.

Let's stick with the program of not sending the guy on a left turn down a dirt road and into the weeds, wasting his time playing around with stuff that CANNOT cause the symptoms he's complaining about; but rather, let's hit all the high-probability failures that are actually capable of creating the behavior at hand.

ede

sofakingdom is a newbie

anesthes

iTrader: (12)

I'm not concerned about post count, I see you registered in Sept. So either your a "newbie" to TGO (welcome!) or your an older user who made a new account after being banned. Which is it?

The second the engine starts cranking there is vac.

No, there is no privileges, and this is not my board. I'm a regular user here, just like you. But I have been here for 7 years, and i've seen this exact problem NUMEROUS times and it always ended up being runner gaskets leaking.

Of course it COULD be a fuel problem, but how many different people would you like to check the fuel system? it's been checked, move on..

The guy is sitting in a cab, turns the key on, looks at the gauge. He has indicated he hasnt seen any issues, he has had a dealer check it out. He himself has checked it out. Why don't you take a fly out there and check it out, so we can move on and check another part of the system.

-- Joe

PhLaXuS

I just wish to corroborate what was said earlier: MAP will not cause a no-start. I had my MAP vacuum line break in half and it initially killed the engine, but upon restart, it cranked and complained and was overall acting way off, but after ~4 seconds, the engine threw a code and it ran roughly normally.

mdkswan

Hi Guys,i'll pick up some start fluid today and check for vac leaks,see if i get a stumble.Thanks Mike

sofakingdom

iTrader: (1)

No, not me!! I'm not like Dean. I haven't reached that level of whatever just yet.

I don't count checking by a dealer as being worth very much. An older vehicle with a swapped engine that the customer is going to eepair himself, is going to get exactly zero attention in their environment. While I in no way discount the abilities and so forth of the techs at dealers, I DO understand the real world that they work in, evidently better than alot of other people. So here's what happened at the dealer. TPI didn't come in a truck. So those guys are going to go to their computer and look up a 71 C-10 or whatever, and they're not going to find much of any help there on the scan of the stone tablet; they're going to look at their book time for a checkout, write the book checkout time on the work order along with a "no defects found" report, go smoke a cigarette, and move on to something that they can make money on. If he's REALLY REALLY lucky, the tech got curious and hooked up a FP gauge or something. But I doubt that even that much actual work occurred there. It would not surprise me if no one actually touched the truck at all.

Although I myself don't work at a dealership, I have one brother who is the service manager at one; another brother who spent about 10 years as a tech at one, and has since moved on; and another brother who was a service writer at numerous dealerships during his career. So I have some degree of familiarity (literally) with what goes on in dealer service departments.

Right, but there's no vacuum UNTIL THE ENGINE IS RUNNING.... which is PRECISELY what isn't happening. So IT DOESN'T MATTER what might happen AFTER the engine starts running, we're concerned about what happens BEFORE the engine starts running. Namely, it has to crank too much.

I'd love to fly out there. I used to live there, and I really liked it. I kind of miss it. But I don't particularly want to go work on somebody else's car (I work on all of my own cars entirely enough, thank you), and I doubt the guy wants to pay for it anyway. There's cheaper ways of getting it done.

So let's move on and leave this vacuum leak thing behind and quit trying to point him away from his lack-of-fuel problem, and start helping him understand how to determine why it takes so long for fuel to become present during cranking. And of course, the first thing is to measure the fuel pressure during cranking; and establish when it is there and when it is not. Which a static fuel pressure reading while the engine is running, doesn't help with. We need to catch the fuel pressure WHILE IT'S MESSING UP, and see what happens that makes it STOP MESSING UP, and make it happen sooner.

Dyno Don

iTrader: (7)

Lets go over what we already know here:

It starts with a shot of starting fluid

When the motor is not running, the map is at max (100 KPA)

So, it could have a vacuum leak but this would not effect starting as it is @ max KPA

At max KPA the fuel is delivered at what is set in the chip tables vs. engine temp (fuel pressure stated is at 42lbs.)

We know it is a modded set up so it has a custom chip (no VATS) because it is a '92 Firebird setup

Recently I have had occurrences where the chip actually had segments that erased themselves in more than one occasion

Since it just started happening just maybe it could be the culprit.

So, that being said, it might be an area to check.

Hope maybe this will shed a little light on the subject.

Zepher

iTrader: (1)

Have you checked to see if the injectors are getting power and are firing?

Have you tried a different ECM?

John 89 Formula

I had the exact same problem with my '89.
I did every test in the book, changed everything from the fuel pump to egr valve to relays, even a new maf sensor, nothing worked. Turned out to be a bad oil pressure switch, replaced it, problem solved.

Hope this helps

1981TTA

First, let me say I agree with the fuel pressure diagnosis approach that's been discussed here.

Second, I think there is some potential merit to a vacuum leak causing start "problems". Keep in mind, the IAC is nothing more than a computer controlled vacuum leak. It is true when cranking a static amount of fuel is commanded based on coolant temp and other parameters. But, it's also true a specific IAC position (i.e. vacuum leak) is commanded at startup based on similar conditions. Depending on the relationship of how much air is being drawn into the cylinders vs. how much air is "leaking" through the IAC (assuming constant closed throttle blade position) the manifold pressure will stay at BARO (IAC Flow = cylinder flow @BARO) or start drawing a vacuum (IAC Flow < cylinder flow @BARO) until an equilibrium is reached. In the case of the MAP staying high, the largest amount of air will be ingested into the cylinders for a given crank RPM. (Kind of a broad generalization, but stay with me here.) In the case of a decreasing MAP, a relatively smaller amount of air will be ingested. If the amount of fuel being injected into the cylinders via calibration at a calibrated IAC opening "assumes" there will be a smaller amount of air when, in reality, there's more air in the cylinder, the mixture will be lean. This would be the condition we could see given a vacuum leak. When the engine was calibrated, they found that IAC position "X" with AFR command "Y" generated the best start under varying conditions. It's also possible that a MAP value close to BARO was experienced during calibration and the "lack" of a sufficient vacuum leak is the problem. I can speak from experience that playing with the startup IAC calibrations does have an effect on both the time it takes the engine to start *and* the RPM "flare" after the engine gets started.

The IAC closed loop RPM control could also be the reason the engine runs fine after starting. (I.e. doesn't show classic signs of vacuum leak.) The IAC position will adjust itself (more leak or less leak) within both mechanical and calibrated limits to maintain a given idle speed.

Again, this is just a hypothesis that was generated to fit the facts of this problem. How severe the vacuum leak would have to be to cause a long crank while being small enough to allow the IAC to compensate would have to be calculated based on the engine parameters and ECM calibration. I just wanted to point out the thought may not be as far out as some might think.

I also wanted to point out that perhaps the computer controlled vacuum leak has a problem. Has the IAC been cleaned and reset recently? The issue could be 180deg from having too much air caused by a vacuum leak. Maybe the problem is a clogged IAC that isn't allowing enough air (or as much as was present when the ECM was cal'd under the same conditions) during crank. Again, the closed loop idle RPM control could mask this problem by opening up further after the engine is running to compensate....

Merlin

How about we put this vacuum leak theory to bed?

To simplify the situation for many of us old timers, consider going out to your old carbureted engine, step on the fun pedal, hold it to the floor (even without a choke) and see if it doesn't fire when you crank it. There is no way in Hades that there is any such thing as even a semblance of vacuum in that skinny little intake manifold when four two-and-a-quarter-inch bores are being held wide open to the world. None. Atmospheric pressure all the way from the air cleaner to the backs of the intake valves. Period. So, is vacuum necessary to start an engine? If you don't remember or understand barometric differential fuel metering devices, try it with your EFI engine. Just remember not to go all the way to the floor, since the "smart" PCM will cut fuel in the Clear Flood Mode with an 80% throttle opening.

And if you were worth a crap at tuning a carb, it would have fired AND run.

GM/Delco Electronics was not so ignorant to require a MAP signal to administer starting fuel in their programming. Not even on the very oldest of their efforts did they overlook starting fuel. Even the old, completely mechanical 1957 Rochester RamJet had a start fuel enrichment cam. The programming was not any different. They aren't Ford, after all.

Vader

Trouble-maker

We've finally established 42 PSI standing fuel pressure. Is that true while it's cranking as well?

And you're using the '730 ECM, correct? Don't overlook the possibility of a "flaky" MAMCAL/PROM, poor connections, and anything related to the TPI swap.

Has this occurred since the weather has turned cooler, or even in warmer weather? I know you mentioned it has happened "whether hot or cold", but is that engine or air temperature? Is the MAT sensor functionng? S/D uses the comparison of the MAT and CTS to trim starting fuel. If you unplug the MAT does it start more easily?

You've established that the 'noid light indicates injector firing. Is that also true while cranking during this no-start condition? As someone asked before, what is the cranking voltage? That affects injector PW in the programming, and you apparently have a custom PROM or have manually bypassed VATS. I'm guessing the former.

I know you can unplug the MAP and it will run. Let's not go there. It should run on nothing but the TPS and HEI signal, and may actually run on only the HEI signal at idle.

Zepher

iTrader: (1)

Oil pressure switch doesn't have to be working or intstalled for the car to run, it is a backup for the fuel pump relay.

If the prom is bad, it should still run in Limp Home Mode. If the entire memcal is bad then I am not sure what the car will do.
I do know that if you have a good memcal and your prom is on an adaptor and you remove the prom from it, the car will still start and run.

Also, a bad dist module can keep it from starting since that pusles the injectors till the engine hits about 300rpm then the ECM takes over.

anesthes

iTrader: (12)

Well, if the checksum is enabled, the code should do a checksum on the whole image at load time, and if it fails will go in limp home mode. So what vader spoke about is possible if the checksum is disabled in the bin.

You sure the dizzy will fire the injectors until 300rpm? I don't see how thats possible looking at the wiring diagram.

There is another possibility I thought of earlier but I won't bring it up until mdkswan gets back to us with more data.

-- Joe

90Formula-X-F

G.M. Tech sitting here scrathing his head wondering if I should even respond. My *** man it's gonna be fuel or spark.

Put all these things out of your mind.

Put a spark tester on this thing so you can see it. Strap a fuel pressure gauge on it and keep a noid light handy It's gotta be missing one of 2 things, fuel or spark.

unless your over fuelling. But if so, it should be loading up.

You around Sacramento area ? Bring it to me I'll fix it !

Vader

X-F,

He mentioned earlier that there is an electric fuel pressure gauge in the cab of the truck, and it indicates 42#. That doesn't mean the injectors are firing, or if the coil is being fired.

No doubt it's a strange one, and that it's getting more confused by all the possible (and mostly valid) reasons that it might not be starting easily. Regardless, it's likely going to be something related to fuel, since he also mentioned that "with a shot of starting fluid it starts right up with minimal cranking." That tells me that starting fuel is inadequate. I'm guessing the PROM is custom (no VATS), and am starting to question whether it is correct, or trying to start on the backup resistor networks. THAT can take a lot of cranking to get it to fire, even at 70°F. The backup parameters will have no start enricnment whatsoever - just enough to keep an engine running.

When you manually administer fuel, it fires up straight away. So what's missing from the "triad of combustion" with that information? Seems easy to me. Finding the reason that there is no starting fuel may not be so easy, but fuel is going to be the key.

John 89 Formula

[QUOTE]Originally posted by Zepher
[B]Oil pressure switch doesn't have to be working or intstalled for the car to run, it is a backup for the fuel pump relay.

Thats exactly what the mechanic said when he installed the new maf sensor which did NOT solve the problem.

I swapped the old maf back in and a new oil pressure switch, and the problem was solved. Had to replace the switch again a week later 'cause the fuel pump wouldn't shut off.

rx7speed

but how would it run after it started if it starts? like crap I'm sure.
think what sofakindom was saying is that if timing was the issue then it would run like crap still after you get it started.
timing wouldn't make it hard to start and then once it started run just fine.

anesthes

iTrader: (12)

I was just pointing out something.. And actually, it depends. I idle my trickflows at 40* commanded BTDC.

-- Joe

anesthes

iTrader: (12)

How did this ever turn out?

Rob Wade

Maybe he got tired of all the argueing!!