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jazzmaster, ASE Certified Tech
Category: Buick
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Buick Century: My 1990 buick century will start run and the

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My 1990 buick century will start run and the shut itself off.The in-tank fuel pump runs and has pressure when key is turned on and as it is being cranked. I replaced the fuel filter.

hi my name is XXXXX XXXXX I will try to help you .

I need to ask you a few questions .

was the old filter clogged up ,that is really dirty and was hard to blow air through .?

do you have an anti theft/security light on ?

does this have an anti -theft ?

you really need to test the fuel pressure with a gauge hooked up to the fuel release schrader valve . the fuel pressure should read 40-47 lbs .

and the pressure should hold for at least a minute and not drop to zero ,it will drop 10 lbs when the key is first turned to the run position and then drop 5-10 lbs ,but should hold pressure for at least a minute or so.

just by seeing whats coming from the tank by unhooking the fuel line may not show you the pressure reading . .

at 40-47 lbs of pressure it would shoot across the shop or street . ...jazzmaster ....

Customer: replied 4 years ago.

The old fuel filter was easy to blow through.I'll get a gauge at the local auto parts store tomorrow and check the pressure at the schrader valve and let you know what it tells me.My car doesn't have an anti-theft option.If there is plenty of pressure ,what else should I look at?

ok, just remember to check the fuel pressure by, turning on the key to the run position

the pressure should read 40-47 lbs on the firsrt turn of the key , it will then drop 5-10 lbs after a second or so.

it is better to see the pressure around 47 lbs but 40 may suffice.

If the pressure goes up to or over 47 lbs and then drains off quick to o-10 lbs it may be that the pump is ok, but the pressure regulator is bad .

you could also have a bad pump as well .

something electrical shouldnt be the issue but lets go with the fuel first ...jazzmaster ....

Customer: replied 4 years ago.



I hooked up the gauge this morning.When I turned on the key,the gauge went to 40psi and stayed there.I then started the car.The pressure went to 36-38 psi and stayed there while the engine was running.It ran for about 4 minutes ,which is a lot longer than usual but then it shut down as if I had turned off the key.The pressure went to 40psi and stayed there but would not re-start.I have spark.

take the ignition module off and run it down to autozone or some other parts store that tests modules , have them check it twice , the nice thing with the testers they have will actually put it under run conditions .

the fuel pressure is a little low but that shouldnt shut off the car like you turned the key off .

I think you have an issue with the module(igniton) and when it heats to a certain point it may be losing a contact inside .

this may still show spark but the injector(ground) pulse is also affected by heat ...jazzmaster ..

please let me know how the ignition module tested out and if need be we can go further into it ..

Customer: replied 4 years ago.

OK ,

I just got back home to check my messages.I'll remove the module and find someone to check it.By the way before I left today I tried to start the car and it wouldn't.

When I got home it fired right up.I t had the same fuel pressure and ran for about a minute.Then I revved it a few times and it shut down not to start again.It'll be tomorrow before I can have the module tested.

ok let me know then , I will be around tomorrow
Customer: replied 4 years ago.

I've called around and Advance Auto Parts and Autozone don't have a way to test ignition modules.Its an expensive part that I'm willing to buy if you are pretty sure that is the problem.Or I could get one from the junk yard.

do you have an autozone or some other parts store near you ?besides advance auto ?

you do have a crank sensor on this car but if that sensor was bad it would most likely have no spark or rpms .

I wouldnt want you to change that part just yet ,there has to be some other parts store that has the tester or an autoxone close to you or perhaps a little ride to it but it will be worth it if you can get the ignition module tested before buying one .

a good clue for a bad module would be no injector pulse to the injectors ,which can be tested easily with a noid light that plugs into the connector that goes to the injectors.

you might want to see if the car will start up by spraying carb cleaner into the air intake /air cleaner hose .

if it starts and runs for a few seconds then you will definately know is the ignition part of the system is working corectly .

you can also try disconnecting the mass air flow sensor and see if it starts as well..

if you have spark/fuel pressure and injector pulse ,the maf sensor may also cause a no start or seems like it wants to start issue ......jazzmaster ...

Customer: replied 4 years ago.

I found an Autozone who would check my ignition module ,but before I removed it I tried the carb cleaner.This morning the car started right up.It shut down about a minute later and wouldn't re-start.I squirted the carb cleaner in the intake and it fired up for about 5 seconds and it shut down.It would then sputter and almost start only after I sprayed more carb cleaner.I disconnected the plug to the MAF sensor it ,and it wouldn't start or sputter.When I sprayed carb cleaner in the intake it would sputter but not start.I haven't checked the injector pulse yet.Would that be checked with a 12v bulb connected parallel to the injector?

ok, good..

ok it seems that the spark/ignition system is working.

by spraying the carb cleaner and it starting and then stalling and the fact that disconnecting the maf sensor didnt change things ,it would be safe to assume that the ignition control module may very well be the issue and its great that you found an auto zone to test it at ..

yes you can check with a bulb connected in the injector connector ....jazzmaster ...

dont buy the module unless the old module tests out bad .

one other thing is sometimes ,that is if the module checks out good ,is that where the module mounts make sure that the serfice areas are clean where it mounts ....

Customer: replied 4 years ago.

I took the module to Autozone and made sure it was warmed up by leaving it on the dashboard,in the sun,with the hot defroster blowing on it.

It was tested about ten times and everything was good.I cleaned it and its mounting bracket. It fired right up,ran for about 30 seconds ,shut down and wouldn't re-start.The Autozone guy recommended checking out the crank sensor.Thanks for the help so far.As usual ,it'll probably be something simple.

yes, ok, the crank sensor is the next thing to look at .

this may or may not throw out a code ,or a stored code .

when the car doesnt start then the next thing is to check the spark, if it appears weak not bright then the crank sensor may be weak or failing.

these sensors do seem to not last as long as they should .

the best/quickest way to check this is with a scanner and monitor the rpms ,if they are erratic or note showing any movement the crank sensor is most likely bad .

if the car has a rpm gauge ,then good ,look at the gauge and see if there is any movement .

no spark as well will point to a bad/failing crank sensor ...jazzmaster ...

Customer: replied 4 years ago.

I hooked a 12volt bulb to an injector.When the car ran for only a few seconds the bulb would light.I couldn't see the bulb light up while I was cranking and the engine not starting ,but the battery died and it is now on charge.

good, but you still need to see if the rpms are good,that is if it is showing rpm movement .

this is best done with a scanner if you can get one or use one or know somebody who does .

Customer: replied 4 years ago.

I don't own one or know anyone who does. A new sensor is cheap.I'll just buy one.Thanks

if you want to just buy one and try it ,fine but I was trying to have it so that you werent buying parts that you didnt need

I am used to using a scanner to help in diagnois vehicles and can understand the stress of kinda guessing and not having access to other diagnoising tools

I am still a little concerned about the fuel pressure,even though the specs call for 40-47 and yours is around 40 ,it is always better to have it read closer to 47 lbs .

that still may be an issue or at the least anproblem that isnt helping matters. I never seen a ful pump that was showing the lower number in the specs cause a vehicle to just shut off .

but the pressure should be higher

Customer: replied 4 years ago.

I ordered the crank sensor and it finally came today.When I tried to remove the old one,it looks as if I might need to remove the harmonic balancer to get the sensor out.It looks like too much trouble.What scanner do I need to use?

any type of scanner that can read rpms or live data will work --a code reader wont .

yeah those balacners can be a pain to get off.

sometimes they come off easy but most need a puller to take them off ..

Customer: replied 4 years ago.

OK .Thanks.

as an added note if the rpms do show movement then we need to go into further testing
Customer: replied 4 years ago.

I've been asking to borrow a scanner and none of my friends have one.I don't want to junk the car so I guess I'll buy one.Will the auto parts know what I need? I replaced the crank sensor, having to remove the harmonic balancer to do so,and it still won't start.It doesn't even sputter anymore when I spray carb cleaner into the intake.I have to work on the car outside and the weather here is nasty now.

ok , there may be other things contributing to it not starting ,that is from all the testing you may have fouled the plugs ,it may be good to check a few of them for being gas fouled/wet, ESP. since the weather is bad ,if it is wet out or cold the fouled plugs dont help the situation . so if they are ,hust take them out and clean/dry them .

Things to also try/do/check ;

please check the spark .it should be bright -with a spark tester -its tough to check with a screwdriver in the plug wire near a ground -such as a bracket or the motor but it can be checked that way -check at least two spark plug wires -as an added note ;

when cranking over the motor see if the spark is not jumping from the wires

sometimes you can disconnect the mass air flow sensor and see if it tries to start then .this may point to a dirty sensor-in that case clean out the resistor in the maf sensor with carb cleaner and blow dry it gently

A scanner is expensive and unless you plan on using it a lot in the future or just using it isnt a good investment .

You may have to take this to a shop to get checked or at least have it diagnoised where then you can replace what needs to be replaced

without a scanner capable of reading the live data-not a code reader scan tool -you are throwing parts in that may not be needed

the important thing is that you can check for basic spark and recheck the plugs to see if they are fouled ;

otherwise, you really need to have this hooked up to a scanner to read the live data

you know the module is good and if it started and ran for a few seconds and then died after sparying carb cleaner into it that shows it had spark at the least ,but as I said from testing may have fouled the plugs enough to now have a no try to start issue .

but spraying carb cleaner may prove that there is spark but wont show if the injector pulse is good ,so check the plugs and check for spark and then let me know ..thanks ///jazzmaster///

Customer: replied 4 years ago.

Checked the spark at the coil points .A good spark jumped the 1/12" gap between them.The front 3 spark plugs were clean and dry.Disconnected MAF sensor and would not even sputter with or without carb cleaner spray.I connected a 12v bulb across tone injector and it didn't light at all.

Still have 40 psi fuel pressure.

I guess its time to tow it to the shop,huh?

first check at the injector connector the dk blue wire to each is the ground signal from the ecm .so while cranking the motor over check at that dk blue wire (injector connector disconnected) and with one end of the test light to bat positive ,then touch the point to the dk blue wire ,the test light should blink if there is a ground pulse coming from the ecm. on the other wire on the connector ,this should show postive bat voltage with the key on and also when cranking over the motor .,let me know what you have ...jazzmaster.

the white wire at the ignition contol module is the tach output ,you can check for tach signal at this wire while cranking over the motor when it doesnt start .


at this point if the ground signal isnt there then suspect the ecm -try tapping lightly on the ecm when it doesnt start and see if that helps it start ,as well as when its running you can tap on it and see if it starts sputtering or stalls out ,if it does then the ecm is at fault

also see if voltage is going to the fuse for the ecm-fuel inj fuse when it wont start although if there is voltage on the one side of the injector at the same time there shouls also be voltage flowing through the fuse/.






there is one other thing that I can think of as well ,try disconnecting one injector at a time and see if it starts and runs ,this will point to a shorted injector ,check the wiring from the injectors as well ,near the alt too as I have seen the wiring rubbing against a ground source or alt casing .the injectors can be tested with an ohm meter ,just disconnect the wiring to each and on the injector touch the meter leads to each terminal of the injector -they should all read consistantly or around 1.5 or so ohms ,if one reads alot higher or lower then that too may be bad .if all this tests good or you are lost with this then it may be time to take it too a shop and in the long run may be cheaper to fix,-as well as you can have them diagnois it and then maybe fix it your self graphic

here is one other chart ,this is a pinout for the ecm ,check the voltages and grounds at the ecm wiring when it doesnt start ,this too may help to pinpoint the issue at hand


Customer: replied 4 years ago.

Sorry . I got sidetracked.

I'm glad to give you a good rating and pay you,but can I come back when I get time to work on the Buick after I leave feedback?

yes you can come back to this question ,just save this post or ask for jazzmaster .

but only rate me ,a good rating ,if you intend on giving me a bad rating ,please post back to me and we can still go further ,but we can go further anyways .

and check the ohms reading for each injector ,

to do that disconnect the injector and ohm it across the 2 terminals on each injector ....

..jazzmaster ....

Customer: replied 4 years ago.


yeah, it looks as you may have a bad injector and this will cause the issues you have .

this is a problem I see sometimes on an older fuel injection system ,also look at the wiring to the injectors,where it runs along the motor ....

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