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Old 04-01-2009, 11:02 PM
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tbi 5.7 1987 chevy suburban

This is about the fifth time I've requested info. Here is the deal; my vehicle continues to fail to start except when it gets a shot of ether. The following has been done to the vehicle;
1) total tune up
2) replaced the fuel filter and fuel pump
3) replaced oil pressure switch
4) total o-ring and gaskets replacement
5) new egr valve
6) new tps
7) idle control motor cleaned inside and out

Ok ya'all whats next????????????? Plan to re-adjust timing tomorrow with a timing light. Any suggestion on timing??????? How do I check the ecm for fault? Limited to a multi meter. The vehicle runs very well after it is started, good idle no backfire. I really thought I solved my problems by changing the oil pressure switch, but no dice. I have watched the injectors while engine is turning over and they appear not to be spraying that vital squirt of fuel to fire my mill. But like I said after the engine fires it runs good. Very frustrated.

Tommy

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Old 04-02-2009, 12:51 PM
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Quote:
Originally Posted by tommy evans
This is about the fifth time I've requested info. Here is the deal; my vehicle continues to fail to start except when it gets a shot of ether. The following has been done to the vehicle;
1) total tune up
2) replaced the fuel filter and fuel pump
3) replaced oil pressure switch
4) total o-ring and gaskets replacement
5) new egr valve
6) new tps
7) idle control motor cleaned inside and out

Ok ya'all whats next????????????? Plan to re-adjust timing tomorrow with a timing light. Any suggestion on timing??????? How do I check the ecm for fault? Limited to a multi meter. The vehicle runs very well after it is started, good idle no backfire. I really thought I solved my problems by changing the oil pressure switch, but no dice. I have watched the injectors while engine is turning over and they appear not to be spraying that vital squirt of fuel to fire my mill. But like I said after the engine fires it runs good. Very frustrated.

Tommy
Your either not getting the fuel pump: 1. when the key is engaged in the Run/Start positions or 2. the computer is not recognizing the engine is cold.

1. The key switch when advanced to the run then cranking position, turns on a timer that turns on the fuel pump relay to supply voltage to the fuel pump. The timer runs the relay for about 10-15 seconds, hopefully long enough to get the engine started. If the computer senses an engine start in that time period, it takes control of supplying power to the pump relay, otherwise, the relay timer will shut the pump relay off in few seconds if the engine doesn't start and the enigne will no longer start with continued cranking unless you back to Off and begin again. Getting a start on a prime fakes the computer and it will supply voltage to the pump relay which in turn supplies voltage to the pump motor. A failure here can run from the ignition switch thru the fuel pump start cycle relay. You will find that if the engine is primed it will start and run but will never start if just cranked off the ignition start circuit with the key. A quick and dirty test is to unplug the connector from the relay and with a jumper from the battery put 12 volts on the power to pump wire. Been a while, I don't remember the color code for sure so get a shecmatic and check it out. If the pump powers up and the engine can be started off the key switch without resorting to a prime, then you know it's the relay or its timer, or some electrical component in that circuit.

Another no start condition is only when the engine is cold, but will start normally when warmed up. Surprisingly, the engine will usually not start cold if the computer doesn't enter into cold start enrichment mode. This is controlled by an engine temperature sensor that is dedicated to the computer, not to be confused with the temp sensor that operates the panel gauge.

Any of these problems can also root in the wiring or the connectors as well as with sensors and relays. You've got to get a decent multi tester and have a wire diagram then go thru the drill to see if things are coming up and in proper sequence. Often when you engage the key it is possible to hear the pump start relay drop it's usually on the engine side of the firewall in front of the driver, so it's close to you when you're seated behind the wheel, also, sometimes you can hear the pump run. If you don't this is a good place to start looking for the problem. As soon as the ignition switch is twisted into the Run position, you should hear the relay latch and the pump start. If you don't tap into the wires and check for voltage when you switch into Run. There should be a voltage to the pump that lasts for 10 seconds or so. Just stop twisting the switch at Run, there is no need to go to Cranking to see or hear this sequence.

Bogie

Last edited by oldbogie; 04-02-2009 at 03:58 PM. Reason: whew, really bad sentence structure! What was I thinking?
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Old 04-02-2009, 05:01 PM
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tbi 5.7 1987 chevy suburban

I will follow up on everything you suggested, but I have installed a toggle switch straight to the pump. It start now. I can actually turn the key off and the vehicle will keep running until I kill the toggle. For any would be thievies it should create real difficulties with any attempt to steal my Burg. If the switch ain't on it will not start. The relay is brand new and was checked today to see if it was getting power. The test light showed power at the circuit. I don't no what kind of sensor I bye past, but whatever it is it is faulty. Thanks for your reply.

Tommy
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Old 04-02-2009, 09:08 PM
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Bogie is right on with his diagnosis. These trucks have an unusual fuel pump circuit as compared to most EFI vehicles. The fuel pump relay is only used for the initial start. Once the engine is running, an oil pressure switch closes and bypasses the relay. If the relay is not working, the engine will start with the ether then stays running because the oil pressure switch is closed. I've got $10 that says it's the relay that's gone bad.
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Old 04-03-2009, 11:46 AM
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tbi 5.7 1987 chevy burg

You might not win your bet. I put a light on that regulator you mentioned and sure enough it had power. Anyways I wired a direct line to the fuel pump connected to a toggle switch to it. No more ether, the vehicle definitely starts now. One of my sensors are faulty, but I was in desperate need of transpo so instead of trying to track down the fault which could of took hours to find I took the short cut. Really can't make any mistakes towards not turning it off because when I turn the key off the truck it will keep running. Once I flip the toggle switch it shuts down the pump. I will follow up on tracing my circuits but I think it is in the ecm. I am just wondering when it comes time to get it inspected there will be an issue about my switch. Well as Willy Nelson says" I am on the road again" See ya. Thanks for your advise.

Tommy
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Old 04-03-2009, 12:11 PM
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Maybe I'm not understanding the power at the "regulator" (relay?), but it may have power to the relay, but it's all for naught if there's no power from the relay.
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Old 04-03-2009, 12:16 PM
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Quote:
Originally Posted by tommy evans
I will follow up on everything you suggested, but I have installed a toggle switch straight to the pump. It start now. I can actually turn the key off and the vehicle will keep running until I kill the toggle. For any would be thievies it should create real difficulties with any attempt to steal my Burg. If the switch ain't on it will not start. The relay is brand new and was checked today to see if it was getting power. The test light showed power at the circuit. I don't no what kind of sensor I bye past, but whatever it is it is faulty. Thanks for your reply.

Tommy
Does this mean that with the toggle switch, there is no problem starting the engine?

I find it odd that with the key off the engine will keep running, where is the ignition getting its power? It should be switched by the key along with the pump.

Bogie
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Old 04-03-2009, 12:30 PM
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Curious, too, how the current is getting in the back door, but if the PCM and ignition can be powered up by hot wiring the pump, this sounds like a thief's dream come true .
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Old 04-17-2009, 11:17 AM
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tbi on a 1987 suburban 5.7 engine

I have made about six inquires on the same subject here is the deal;my vehicle will not start unless I squirt a shot of ether into the injector. I actually wired a toggle switch straight to my fuel pump to activate it. Even though I can hear the pump running the doggone vehicle still fails to start. I had the system running perfect about week ago until the toggle switch broke and the connection in the rear some how shorted out. I fixed the short put a heavier switch on the circuit but now the vehicle won;t start without a shot of either. Hey i got all new oil pressure switches and a new relay. Still wont start
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Old 04-17-2009, 02:36 PM
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power to the pump

Quote:
Originally Posted by oldbogie
Does this mean that with the toggle switch, there is no problem starting the engine?

I find it odd that with the key off the engine will keep running, where is the ignition getting its power? It should be switched by the key along with the pump.

Bogie
I wired the toggle switch straight to the fuse box. Hooked it to a 20amp fuse. Then ran a line to the pump. Well that worked great for about a week until some how the wire shorted out and my doggone toggle switch broke at the same time. Ok back under to fix the short. I taped it up real good and repair was made. Got a heavy duty toggle switch and wired that up. Ok here is the results; my fuel pump will come on when the ignition switch is turned on and the toggle switch is put in the on position. Here is the problem; my fuel pump is running, but my vehicle still will not start unless I squirt some ether into the tbi??????????? Bye the way I timed the vehicle with a light and just replaced the oil pressure switch, relay and oil sending unit. The vehicle has a new coil and rebuilt gasket set.
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Old 04-17-2009, 03:40 PM
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Quote:
Originally Posted by tommy evans
I wired the toggle switch straight to the fuse box. Hooked it to a 20amp fuse. Then ran a line to the pump. Well that worked great for about a week until some how the wire shorted out and my doggone toggle switch broke at the same time. Ok back under to fix the short. I taped it up real good and repair was made. Got a heavy duty toggle switch and wired that up. Ok here is the results; my fuel pump will come on when the ignition switch is turned on and the toggle switch is put in the on position. Here is the problem; my fuel pump is running, but my vehicle still will not start unless I squirt some ether into the tbi??????????? Bye the way I timed the vehicle with a light and just replaced the oil pressure switch, relay and oil sending unit. The vehicle has a new coil and rebuilt gasket set.
OK I though that when you wired the toggle switch the problem went away.
Is this a wrong conclusion on my part?

Now for some stupid questions but humor me.

1) Am I correct in thinking that this is only required for a cold start?

2) Is it required for a hot start as well? If not, how much time passes as the engine cools before you have to ether it again to get it going?

3) Will it start from a prime of gasoline, or is only something really volatile like ether able to fire it?

4) It's eyebrow singing time! With the air cleaner removed like you were going to give it an ether blast, with someone else cranking and you looking down the throttle bores, do the injectors shoot fuel when the engine is cranking?
Wear a face shield otherwise you just might end up with those singed eyebrows.


So you know what I'm thinking about, I'm trying to separate some conditions. 1) If this is a cold start issue caused by the computer or a sensor.

2) An injector problem.

3) An ignition problem

4) A wear problem with the timing chain and gears.

5) A compression or leak down problem.

6) A cam and lifter or pushrod and rocker wear problem.

The first 4 questions are aimed at the injection system with a touch on the ignition. We'll get deeper if this doesn't expose something.

Bogie
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Old 04-17-2009, 04:54 PM
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Quote:
Originally Posted by oldbogie
OK I though that when you wired the toggle switch the problem went away.
Is this a wrong conclusion on my part?

Now for some stupid questions but humor me.

1) Am I correct in thinking that this is only required for a cold start?

2) Is it required for a hot start as well? If not, how much time passes as the engine cools before you have to ether it again to get it going?

3) Will it start from a prime of gasoline, or is only something really volatile like ether able to fire it?

4) It's eyebrow singing time! With the air cleaner removed like you were going to give it an ether blast, with someone else cranking and you looking down the throttle bores, do the injectors shoot fuel when the engine is cranking?
Wear a face shield otherwise you just might end up with those singed eyebrows.


So you know what I'm thinking about, I'm trying to separate some conditions. 1) If this is a cold start issue caused by the computer or a sensor.

2) An injector problem.

3) An ignition problem

4) A wear problem with the timing chain and gears.

5) A compression or leak down problem.

6) A cam and lifter or pushrod and rocker wear problem.

The first 4 questions are aimed at the injection system with a touch on the ignition. We'll get deeper if this doesn't expose something.

Bogie
This condition happens cold or hot.Never tried just gasoline.Oil pressure reads 50lbs on my gauge, that should eliminate #4,#5,#6 questions. The vehicle runs very well after it has been started. I checked the spray of the injectors while the vehicle is running, nice cone shaped spray. I don't think the injectors are bad but something is stopping the tbi from getting a prime. I will have to check while cranking if any fuel is squirted out from injectors. Up to this point do you see any conclusions?
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Old 04-17-2009, 04:56 PM
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Have you checked the fuel pressure? if it`s not getting fuel pressure it`s not gonna run. Also I would never run a fuel pump to a toggle switch, this is not safe as if you wreck and are unconcious and a fire breaks out, well, you know the rest of the story. It`s also possible something in the distributor is off, as if I recall correctly it`s the distributor that sends the pulses to the injectors.
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Old 04-17-2009, 06:01 PM
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Quote:
Originally Posted by tommy evans
This condition happens cold or hot.Never tried just gasoline.Oil pressure reads 50lbs on my gauge, that should eliminate #4,#5,#6 questions. The vehicle runs very well after it has been started. I checked the spray of the injectors while the vehicle is running, nice cone shaped spray. I don't think the injectors are bad but something is stopping the tbi from getting a prime. I will have to check while cranking if any fuel is squirted out from injectors. Up to this point do you see any conclusions?
Let me start by saying that 50 psi oil pressure doesn't eliminate any questions. You gotta do this by the drill, when you start assuming things, stuff gets over looked.

I'm not assuming bad injectors, I want to know if they're flowing fuel when the engine is being cranked. If they aren't the engine will never start without help, at issue here is a completly different circuit is involved with cranking than running. Somebody got you off on the wrong track with oil pressure, the computer doesn't give a damn about oil pressure, its looking to idle speed. The oil pressure safety circuit is a dumb switch that simply kills the fuel pump power circuit if oil pressure is lost. It rightly or wrongly assumes the vehicle has been tipped over and oil pressure has been lost which can be used to shut off the electric pump, which would otherwise keep pumping. Some systems use a up/down switch letting gravity seat the switch, the problem is sensitvity between a high G turn or a flipped vehicle.

So we still need an answer to questions 3 and 4 these are really important.
Which are:
3) Will it start from a prime of gasoline, or is only something really volatile like ether able to fire it?

4) It's eyebrow singing time! With the air cleaner removed like you were going to give it an ether blast, with someone else cranking and you looking down the throttle bores, do the injectors shoot fuel when the engine is cranking?
Wear a face shield otherwise you just might end up with those singed eyebrows.


Bogie
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Old 04-17-2009, 08:39 PM
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had this sameproblem on a tbi 4.3L and we were stumped for a year even after new pump andother parts

ended up being bad pink wire from coil to distrib

was broken inside the insulation to where you could not tell visually it was broken

figured it out one day when it did fire up(randomly) and was messing with the wires while running and it died

20 bucks later with a new coil harness from chevy dealer parts counter and it was fixed like brand new forever since


good luck
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