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  #16 (permalink)  
Old 11-04-2015, 07:13 AM
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Fuel pump is kicking on, If i "prime" the system it only cranks 2 or 3 times. I dont think i am gonna get under that as i run 15w-40 in it. It's 6 cranks before fire if i dont turn the key on position and back off 4-5 times. On a hot start it fires right up, youd think it was MPI. TPS is good, IAC is great, i did rebuild the TBI and didnt adjust base-idle. Do i need to do that? I think the pressure is just bleeding off somewhere.

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Old 11-04-2015, 12:32 PM
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TBI motors usually don't have a fuel pressure test port..

the pump should make 25 to 27 PSI instantly when deadheaded at the filter..

what.. i usually keep an extra filter around.. with a section of proper fuel line threaded into one side.. a chunk of hose.. to hook my pressure gauge to..


this is a 10 second MAX test.. fuel pumps don't like to be dead headed..

do you have a digital volt meter that has at least a 10 AMP DC setting..

if so.. find the fuel pump fuse. remove it.. set the meter up... use the probes held lightly without spreading the terminals into the fuse holder... have somebody start the engine.. i like to see less than 7.1 amps..

you might want to invest in one of these.. since you use the full size fuses. 30 Amp Automotive Fuse Circuit Tester
some stores may also have the 20 amp version.. if they do buy both.

if you remove the fuel pump relay.. you can with some care remove the cover from the relay.. plug it back in. give it a squeeze to turn on the fuel pump without the engine running.. the fuel pump amp draw should be really stable.. not bouncing all over the place.

i have found so many pumps that the bushings are worn away. the armature just wobbling back and forth rubbing on the half shell field magnets..

1990 S10 Idle Surge fuel pump shafts worn - Album on Imgur


Throttle body setting..

engine off.. grab the throttle lever... open it slightly.. wiggle.. you should NOT have any front to back play.. or very very little.. the throttle shaft bores wear .. so instead of this.. (O) you get movement when you open the throttle ( O) to this(O ) this effects the angle the throttle shaft closes to..

if the TPS voltage is not exactly the same each time the throttle closes.. you will confuse the computer..

do you have any friends with a scan tool to display LIVE data stream on these systems... snap on MT2500s, OTC monitor 4000s, monitor extended.. extended monitors.. genisys. autoxray units, actron CP9110 versions.

do you have a digital volt meter?? so you can check the TPS voltage..
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Old 11-04-2015, 01:05 PM
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Yes i have a digital voltmeter and have already tested the TPS. Its tested good. I will check the throttle. Fuel pump is new so i really hope it isnt the issue. Not expensive but just a waste of money. I dont have a scanner for live data and i dont know anyone who does. There is no SES or CEL light anymore. Annnnnnd when i pulled in my driveway i thought i would be funny and mess with my dogs so i went to give her some throttle and heard a pop from the engine bay. Thought it was back fire. But when i put it in park and gave it some revs i got nothing. I back down my drive and headed back up in the same mannor and nothing. Not sure what it was. I dont have a Catalytic converter (not that it would even have anything to do with it) Just not sure what would have made the sound. I check my plugs and they are fine. When going down the road and coming up on a hill i can put my pedal half way to the floor and still be losing speed. My engine doesnt gain rpm or anything just seems like its starving for fuel. I can hear the fuel pump kick on when i turn my key and i can hear the relay as well. Im just at a loss with no scanner.
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Old 11-04-2015, 01:32 PM
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Retested my TPS, its getting .586 V at idle and 4.1-4.280 at WOT (key turnde to on and engine off of course) Shouldnt it be 4.5-4.6?
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Old 11-04-2015, 01:43 PM
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that TPS reading is perfect..

can you verify that each time it closes it reads the same..


did you see about stuffing a rag into the idle air bypass passage to block it.

then adjusting T15 idle stop screw to a very low idle speed... pull the shop towel back out and the idle will surge.. don't worry.. grap the throttle and take the RPMS to 1500 to 2000 and hold it stable there for 20 seconds.. then slowly return to idle.. that gives the computer the time to relearn the idle air position. you can shut it off.. wait 10 seconds and restart it without touching the gas..

this is a manual that covers both TBI and PFI for marine applications.. but it is the same testing for your preobd2 system. there is some there that does not cover your system. but a great idea.. in the first few pages . look at the CLEAR FLOOD mode.. that is why you need to have the TPS at the proper position and NOT vary..

http://www.weindex.info/pdf/FuelSystem/9.pdf
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Old 11-04-2015, 06:07 PM
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Quote:
Originally Posted by waynep712 View Post
that TPS reading is perfect..

can you verify that each time it closes it reads the same..


did you see about stuffing a rag into the idle air bypass passage to block it.

then adjusting T15 idle stop screw to a very low idle speed... pull the shop towel back out and the idle will surge.. don't worry.. grap the throttle and take the RPMS to 1500 to 2000 and hold it stable there for 20 seconds.. then slowly return to idle.. that gives the computer the time to relearn the idle air position. you can shut it off.. wait 10 seconds and restart it without touching the gas..

this is a manual that covers both TBI and PFI for marine applications.. but it is the same testing for your preobd2 system. there is some there that does not cover your system. but a great idea.. in the first few pages . look at the CLEAR FLOOD mode.. that is why you need to have the TPS at the proper position and NOT vary..

http://www.weindex.info/pdf/FuelSystem/9.pdf
YEs, i can verify it is a solid .586 everytime it closes. About how many turns should i adjust the idle screw and can i access the IAC valve with it on the motor? I have never tried. I will do it tomorrow in the daylight since the world seems to think it has to get dark at 6:30. Should i leave it set at the lower idle or readjust back to "normal" i dont have a Tach so not sure what it idles at. But i do sometimes have to give it some throttle while its idling to get it to go into closed loop (idle lower like its supposed to) I dont know how many miles are on the motor since it isnt the original. Also when i took the TBI off i noticed the IAC doesnt sit flush, it is alway open a little, is it supposed to be?
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Old 11-04-2015, 07:28 PM
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there is a passage on the passenger side top of the throttle body.. above the idle air control valve.. kinda behind the hold down bolt to pack with the rag to block the bypass air to set base idle..

page 9 of this.. procedure B. but read the other ones also..

http://www.askatech.com/AskATechLive...Track/G067.pdf

you may also want to read this..

http://www.gmcmidwestclassics.org/We...0the%20TBI.pdf


both don't cover it exactly like i described.. but you have not mentioned if you have access to a scan tool.. so i am taking that you don't..

well actually the upper link comes close.. as it says to use the thexton plug. but i found that they don't always fit.. so i just stuff a shop rag in it filling the cavity.. this is a 2 minute procedure.. it takes longer to warm up the engine and take the air cleaner off than it does to do this..

sorry i cannot pass 35 years of knowledge thru my fingers .. would you like to talk.

edit... http://www.askatech.com/AskATechLive...Track/G083.pdf

Last edited by 69612; 11-04-2015 at 07:52 PM.
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Old 11-05-2015, 07:25 AM
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I dont have access to a scan tool. I wish i did. My motor is warmed up right now as i took my son to school. I will go out and perform this test and let you know.
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Old 11-05-2015, 07:49 AM
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Okay i dont what you said/what i read. Didnt seem to affect it any. The way it acts is almost like an injector is shutting off sometimes. Just boggs when i go to give it gas to go up a hill or even pick up speed. Only does this under load. Light acceleration its fine. If i punch the pedal it falls on its face. I am just going to have to assume for now its a Fuel pressure issue until i can get a gauge to put on it.
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Old 11-05-2015, 09:03 AM
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that description of bogging if you give it any throttle.. aims right at fuel pump failure..
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Old 11-05-2015, 10:26 AM
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Well New doesnt always mean good i suppose. I guess ill just have to replace it again.
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Old 11-05-2015, 10:42 AM
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Quote:
Originally Posted by LATECH View Post
Several years ago I had an 89 that came in to be checked out for a very similar problem.
Took some looking to find it, but....and I am not saying yours will be the same but....I found the wire to the pickup coil in the distributor were corroded almost in two. I replaced it and it must have been the problem because it fixed it.
Funny thing is it still had spark but wouldn't spray the injectors.
Must have been sending a signal that was too weak to Feed the Ignition and the ECM
That being said, the TBI system is very good at startup especially cold as it sprays the fuel, promoting atomization, unlike a carb that requires the fuel be siphoned through small orifices in the carb before it even atomizes .
A TBI is a very dependable cold starting system even in the face of -25 degrees and better.
I wouldn't worry about any timing chain problems at this point as it is a dual row chain and not the morse silent type. The dual row is used in roller cam engines because it is less prone to allow timing fluctuations due to design alone.
I would try spraying down the throttle and then try to start it first thing in the morning to see what you get.If it starts with a spray then fuel is lacking for some reason.
It would really benefit the diagnostic routine if you had a pressure gauge on the system to verify cold startup pressure or lack of, or slow to build pressure.
Better to diagnose than to throw parts at it.


One other option for cold startup fuel starvation (a presumptive test) would be to turn the key on don't crank, wait 2 seconds. This cycles the fuel pump by using the ECM 2 second pulse that turns the fuel pump on to prime the system. You can cycle the key 4-5 times. Be sure to listen to be sure the fuel pump relay is indeed cycling. Then after that see if you get a decent cold startup.
If that seems to help the startup situation the it is likely the pump check valve is not holding or the line in the tank between the pump and the fuel outlet line is leaking.


At any rate you really need to nail down if your cold start problem is fuel related.
Be sure the fuel pump relay will cycle and that it is powering the circuit
Get a fuel gauge and hook it up.
Stop guessing at it.
The factory did not use a roller chain in flat tappet cammed engines and did not use a double row roller in roller tappet engines it was single row roller which does have a bit better life than the morse chain over a plastic tooth gear b ut not near the life of a double row roller chain.

Bogie
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Old 11-05-2015, 01:04 PM
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Quote:
Originally Posted by oldbogie View Post
The factory did not use a roller chain in flat tappet cammed engines and did not use a double row roller in roller tappet engines it was single row roller which does have a bit better life than the morse chain over a plastic tooth gear b ut not near the life of a double row roller chain.

Bogie
Fuel Relay on mine kicks on everytime but the pump itself only kicks on everyother time ( if i cycle the key and dont start the engine.) Doesnt matter if i do it right after the fuel pump kicks off or wait 2 minutes the second time only the relay kicks. Shouldnt the pump kick on everytime?
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Old 11-05-2015, 04:46 PM
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The relay contacts could be worn or burned away.. that is why i ask most people to remove the relay and inspect the contacts.. then do mechanical squeeze the bare frame relay tests.. to see if the pump kicks on every time..

i ask them to get the truck started.. then pull the fuel pump relay out.. the engine should NOT die.. if it dies then the oil pressure switch is bad.. even if it shows good oil pressure.. the fuel pump circuit contacts are completely isolated from the oil pressure circuit in the sending unit.



GM trucks up thru 2003 used an oil pressure switch as a redundant circuit for the fuel pump power.

a worn out fuel pump will usually fail to spin up sometimes.. doing a FONZ slap to the bottom of the fuel tank while somebody is cranking the engine may get them started..

i had to lay under a minivan with a big rubber mallet with a relay extender/remote starter button wired to a old relay to get the pump to run enough to pump the fuel out of the tank.. it was filled to the neck.. it took me a while to do it..

testing failing pumps is why i use the amp meter.. the amp draw should be steady.. not surging..
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Old 11-05-2015, 06:06 PM
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My oil pressure gauge is normally maxed out will occasionally on a perfect day work intermittenly. So Oil pressure sender could actually be the root cause of this. I will check the relay tomorrow in the light and if it dies ill replace the Oil sending switch and go fromt there. Also another thought i had, if my Injector(s) are fouling out at Operating temp could that cause it? After it warms up i noticed today it has a slight miss. But only does it in closed loop at normal operating temp.
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