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get somebody to listen to the fuel pump.. while you turn the key on.. does the fuel pump come on for 2 seconds at Key ON. then turn off.??

if not.. replace the fuel pump relay.. 89 should be over on the passenger side of the firewall under the hood.. it will have a small black wire that is connected to ground.. a ORANGE Wire that is hot all the time. a Green and white stripe wire.. DO NOT probe this wire with a test light.. i am giving you wire colors to identify the relay location.

at key on the ECM sends positive power to the Green wire with the white stripe.. that closes the relay for 2 seconds at KEY On.. then it turns it off if it does not see the Cranking signal from the ignition switch to the ECM.. and it will turn it off if it does not see RPM from the distributor Pin B on the 4 pin connector.

get your engine started... reach over and disconnect the fuel pump relay.. the engine should continue running.. if it dies.. then replace the 2 prong or 3 prong oil pressure switch/sender...

what.. the fuel pump relay is controlled only by the green white wire from the ECM.. when the engine is running the oil pressure switch which has 2 circuits on the 3 pin version will connect the outer 2 pins to power the fuel pump with the oil pressure up..

if its a lot of cranking cold but not so hot.. change the fuel pump relay.. repeat the test above.. key on 2 seconds of fuel pump operation.. cranking you should have fuel pump operation..

if you have not changed the engine coolant temp sensor. SU102 at AZ is under 20 bucks for the sensor and pigtail.. both the sensors and the pigtails go bad.. tell the computer that the engine is way over temp.. if you disconnect the coolant sensor you should get a code 14.. if you clear the codes and jump the yellow wire to the black wire and turn the key on you should get a code 15. this proves the wiring to the sensor has not failed inside the harness.

there is more to accomplish.. like setting base idle on the TBI..

engine at operating temp.. stuff the idle air bypass passage full of shop rag.. you should have a fairly low idle speed.. you want 1/2 to 3/4 turn of the idle stop screw above the point where the throttle blades bind in the bore and stick closed.. if you had access to a scan tool to look at live data..

engine warmed up to operating temp. coolant temp over 195F.. TPS voltage below 0.98 volts.(0.45 to 0.75Volts DC throttle closed). IAC (idle air counts ) 20 to 50 is the perfect spot for them. if your throttle shaft bore is worn.. you will have issues..
 

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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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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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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/AatFileShare/References/FastTrack/G067.pdf

you may also want to read this..

http://www.gmcmidwestclassics.org/Web pages/Tuning the TBI.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/AatFileShare/References/FastTrack/G083.pdf
 

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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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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.
with a hot misfire.. i would examine the ignition coil for signs of high voltage leaks.. white marks around the outside of the windings. there is a chance your injectors could be shorting internally..
 
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