1990 Buick Century Engine will not start and stay running

Tiny
RALBON
  • MEMBER
  • 1990 BUICK CENTURY
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 63,000 MILES
When the engine starts, it will run rough like it is missing on several cylinders. It will also backfire thru the intake. I changed the spark plugs, cranksensor, and all four of the relays, and the coolant sensor. I checked the ohms on the injectors and five of them have 12.2 ohms and one has 8.0 ohms. With the ignition, on the pink wire of the injectors all have 11.7 volts. When I first replaced the cranksensor, the engine started and ran very good. About an hour later I tried to start the engine and it ran very rough and then stalled. Also, I had the ign module checked at a local parts store and the module passed, and they checked 3 or 4 times. I don't have enough money to change everything on this engine. Also, I keep getting a trouble code of 42, which is the spark timing circuit. I am lost on this one, please help. Thank you very much.
Saturday, October 3rd, 2009 AT 6:36 PM

19 Replies

Tiny
MATHIASO
  • MECHANIC
  • 1,209 POSTS
What we have here is a failure to communicate?

The ignition module and the computer are in constant communication when the engine is in operation. (Over 400 RPM.)With the computer telling the module the correct timing. If communication is lost or a circuit becomes infected with false signals (bad grounds, short to battery +, Electro Magnetic Interference spark plug wires to close to circuit wiring, oil contamination of the circuit connectors and wiring) then the computer will turn timing control back to the ignition module and flag the code 42.

If the crk and the cam are not synchronized or if the routing of the spark plug wires are close to the EST circuit(s) wiring.
Alldata has a very good on-line manual system for the DIY?S that contains all the information and a trouble?Tree? Chart(s) for the proper method to test computer for your vehicle.
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Sunday, October 4th, 2009 AT 6:19 AM
Tiny
RALBON
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Hello Mathiaso: I understand what you are saying, but I don't know where to start or how to accomplish what you are saying. If I have a short or a bad ground, how do I check for those things and elimanate the problem? Thanks

The ignition module and the computer are in constant communication when the engine is in operation. (Over 400 RPM.)With the computer telling the module the correct timing. If communication is lost or a circuit becomes infected with false signals (bad grounds, short to battery +, Electro Magnetic Interference spark plug wires to close to circuit wiring, oil contamination of the circuit connectors and wiring) then the computer will turn timing control back to the ignition module and flag the code 42.

If the crk and the cam are not synchronized or if the routing of the spark plug wires are close to the EST circuit(s) wiring.
Alldata has a very good on-line manual system for the DIY?S that contains all the information and a trouble?Tree? Chart(s) for the proper method to test computer for your vehicle.[/Quote]
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Sunday, October 4th, 2009 AT 10:00 AM
Tiny
MATHIASO
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It is no way with a magic triks to solv this problem, before solving any problem, it is important to understant the root cause of it. Have put out a number of possible causes, like spark plugs wire vlose to other circuits.
You change the crk, what about the cam?
The code 42 is a challenging code, Alldata can be a good help for you as I describ it.
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Sunday, October 4th, 2009 AT 1:51 PM
Tiny
RALBON
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This engine has the cam and crank sensor as one unit. Did the ohms on the injectors mean anything to you. What will a good injector be ohm wise. While running the fuel pressure is 35 and 45 with engine off. Why would wires that have been in the same place since the car was new, be causing a problem now? I got the car started and tapped on the computer and the engine would either die or run better, does this mean anything? How do I check for a short or a bad ground? If you cannot help any more than you have so far, then you should refer me to someone else or refund my donation. Thanks
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Sunday, October 4th, 2009 AT 2:15 PM
Tiny
MATHIASO
  • MECHANIC
  • 1,209 POSTS
Your injector reading should be between 11 and 18 ohms.
Replace the injector that was low, it should not be 8 ohm. Check fuel regulator, remove the vacuum line feeding the fuel pressure regulator, check for the presence of fuel, if fuel is present the diaphragm inside the regulator has ruptured and is feeding raw fuel into the engine causing it to run rough.
In most cases 45 p.S.I. To 55 p.S.I. Is standard in port injection system. Your fuel pressure might be little low too
what do you think?

Let me know what you find.
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Sunday, October 4th, 2009 AT 3:02 PM
Tiny
RALBON
  • MEMBER
  • 11 POSTS
Hello mathiaso -- I haven't been able to get back to the buick yet but I will soon and will let you know what I find, don't give up on me. Thanks
[quote="mathiaso"]your injector reading should be between 11 and 18 ohms.
Replace the injector that was low, it should not be 8 ohm. Check fuel regulator, remove the vacuum line feeding the fuel pressure regulator, check for the presence of fuel, if fuel is present the diaphragm inside the regulator has ruptured and is feeding raw fuel into the engine causing it to run rough.
In most cases 45 p.S.I. To 55 p.S.I. Is standard in port injection system. Your fuel pressure might be little low too
what do you think?
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Wednesday, October 7th, 2009 AT 8:45 AM
Tiny
MATHIASO
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Thank you buddy, keep me updated, we will work on it together.
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Wednesday, October 7th, 2009 AT 2:50 PM
Tiny
RALBON
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Hello Mathiaso: finally got a little time to check on buick---No gas in hose to regulator, cleaned all the grounds that I could find -- disconnected all the sensors except the ones that are needed to start. Started the engine, no difference, still runs very rough, it did run long enough to check the firing -- have a dead miss on #3 no fire at all -- These are the original wires on this car, should I change them or is it the coil? While it was running I tapped on the relays and the engine shut off. I did reconnect all the sensors, but did not make any difference. Also, the gas smells unusual, could this be bad gas? Thanks again, God Bless
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Sunday, October 11th, 2009 AT 1:15 PM
Tiny
MATHIASO
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What about the injector that was 8 ohms, was it on the # 3?
Suppose it is a 3.1 L
swap the # 3 to one on the opposite of the coil
and swap theone on the opposite of the coil to #3
this will determine if the problem is in the ignition coil or not.
If the misfire remain on #3, then the coil and spark plug wire are good if misfire goes to the a new cylinder then the coil need to check.
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Sunday, October 11th, 2009 AT 2:13 PM
Tiny
RALBON
  • MEMBER
  • 11 POSTS
The injector that is 8 ohms is on # 2. I have a coil off of a 95 cutlass 3.1 will that coil work for a check -- This engine is a 1990 3.3. What is causing the engine to shut off as if you turn off the key?
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Sunday, October 11th, 2009 AT 9:54 PM
Tiny
MATHIASO
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3.1L (VIN T and M) engine without distributor Firing order: 1-6-5-4-3-2 Distributorless ignition

3.3L engine without distributor Firing order: 1-6-5-4-3-2 Distributorless ignition

yes they have the same firing order and derfor should work

yes that another way to to test the coil.
yes this could make the engine to shutoff too because of lot off unburn gas, computer shutt it off to avoid inondation.
you told me you smell lot of gas don't you?


https://www.2carpros.com/forum/automotive_pictures/46384_33_l_1.jpg

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Monday, October 12th, 2009 AT 2:26 PM
Tiny
RALBON
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Hello Mathiaso: I don't smell a lot of gas, the gas seems to have a bad smell when I am around the charcoal canister -- The coils on the 3.1 are numbered diffently -- anyway I tried one of the coils off the 3.1, which is running good, and it didn't help any -- maybe I should try all of them -- I am sure leaning toward PCM being the problem -- I can get a used one from the local saolvage for $40.00 -- maybe it will be worth a try -- had the ign mod checked aagin by a different parts store and it checked good -- I am really stumped on this one --
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Monday, October 12th, 2009 AT 2:58 PM
Tiny
MATHIASO
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When there strange smell of gas around the canister mean that there is a problem. The filter in the canister may be need to be replace.
If you can get a vacuum pump, remove purge solenoid valve, apply vacum, the vacuum should be maintain, if the vacuum is not maintain, the solenoid is leaking and tthat cause the problem you are having.
Test the purge solenoid, the canister valve,
just remove the hose on each and apply vacuum.
Vacuum should be maintain.
The charcoal canister has filter that should be checked once a year. Or every 15000 miles, it may be soacked with lot of gas, replace it.
Forget the coil for this time, test those components and let me know.
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Monday, October 12th, 2009 AT 4:48 PM
Tiny
RALBON
  • MEMBER
  • 11 POSTS
Hello Mathiaso, I checked the purge valve and it will not maintain vacuum. I have not removed the canister yet, evidently the purge valve is bad, what next? Also, this may not mean anything, but when check for trouble codes and turn on the key all the lights come on the dash, and the engine light blinks like it is suppose to, but if the temp light goes out the engine light will blink very fast until the temp light comes back on, this is really getting weird. Thanks Mathiaso
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Tuesday, October 13th, 2009 AT 3:43 PM
Tiny
MATHIASO
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You did a good job, you do not need to remove the canister. Just replace the valve, that will take that smell away or may be the answer to our problem
now let's go back to the coil.
Now, on the coil, swap the cable on the #3 and #6.
I mean put the cable on # 3 to #6 and from #6 to #3.
Let me know if the misfire is still on # 3 or have move to #6.
This step is very important.

I'm waitting.
You did a good job.
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Wednesday, October 14th, 2009 AT 2:33 PM
Tiny
RALBON
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Hello Mathiaso:-- I swapped the wires on #3 and #6 still no fire and also I checked all of them again and now I have no fire on #2, #3, #4, #6 -- it is only firing on # 1 and # 5 --- keeps getting worse. What do you think?
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Friday, October 16th, 2009 AT 3:53 PM
Tiny
MATHIASO
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The problem is probably with the coil.
You will need to change it.
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Friday, October 16th, 2009 AT 6:01 PM
Tiny
RALBON
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Hello Mathiasol: Well, I changed all three coils, the engine started, I drove it around for a while and parked it. About an hour later, no start, back to the same thing. We haven't nailed it yet. Thanks Mathiaso
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Tuesday, October 20th, 2009 AT 5:42 PM
Tiny
MATHIASO
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Do not worry, it not the end of the world yet :-)
Do you still get engine light with code 42?
That code is associated with ignintion module.
Then have the Crank Angle Sensor (CAS) looked at with a scanner. If all checks are okay, replace the ignition module.
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Tuesday, October 20th, 2009 AT 7:52 PM

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