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1990 STS does not pass emission check


jlinde

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I am trying to help a friend with his 90 STS which does not run on all 8 cylinders when warm.

When I do the injector shut off test (from instrument panel) when warm 2 of the injectors don't decrease the rpm(cyl 4 and 7)

Did this test 7-8 times to be sure. Pulled and checked the number 7 spark plug -looked perfect.

When ign cable for #4 and #7 were taken away from distributor it was clearly felt.

No ECM codes except the E052 for disconnected battery.

Plugs, cables, distributor cap, heat sensors and tps as well as oxy sensors are all new.

Around a year ago 1 fuel injector was replaced - Can it be so that even more injectors are

bad (4 and 7) but all of them give the 'click sound' in the stetoscope when I listen to it.

/Jan L

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There is unmetered fuel entering the engine at some point. Either the injectors on #4 and #7 are leaky or the fuel pressure regulator is bad. If you remove the vacuum line from the FPR and turn the ignition to ON, there should not be any fuel leaking out of the FPR nipple. If there is, the FPR is bad. You may need to let the car idle with the vac. line disconnected from the FPR and watch for fuel from the FPR nipple. Be sure to use a golf tee or pencil to plug off the vacuum line.

If the FPR checks good, then you'll need to remove the fuel rail and turn the key to ON while observing the injectors. There should not be any fuel dripping from the ends of the injectors. Pay close attention to the injectors for #4 and #7. You could also swap the suspect injectors with two other cylinders and then turn off the injectors to the cylinders you moved injectors #4 and #7 to and if there is no idle speed drop, then the injectors are bad.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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i thought a intake leak results in high CO readings? or more air getting in than is normal or another way to look at it is less fuel being delivered than expected. if your injectors are not working than you should be getting more air vs fuel, not more fuel vs air.

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i thought a intake leak results in high CO readings? or more air getting in than is normal or another way to look at it is less fuel being delivered than expected. if your injectors are not working than you should be getting more air vs fuel, not more fuel vs air.

High HC readings are the result of too much fuel entering the combustion chamber. Excess fuel can enter via an injector that has a pintle seal that is not sealing or a bad fuel pressure regulator.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I have not done anything specific yet with my friends 90 STS but I searched the net and when reading

I experienced that there is a lot of writing about problematic injectors for the 4.5-4.9 (The Northstar injectors don't seem to be as faulty as I can understand it) and even the ECM can be the problem source. I do not have any extra ECM but I have a good set of injectors for a Mustang 90 GT which are possible to use according to different sources. The Mustang has #19 and Cad #18 and pressures are 39 psi and 43 resp. So the Cad will get some more fuel because of this but the oxy sensors

will maybe take care of this. So I think I will do a test with with those Ford spec injectors - the 4.5 runs so bad now so anything is worth trying. I also think I will advise the friend-owner to invest in an extra ECM out of Ebay (for my own 93-94 Northstars I have a couple of extra engine computers).

The idea of moving the injectors around is of course good but it will take a little more time? than just installing injectors that all work from the start - at least they did a couple of weeks ago. Injectors for the 4.5 Cad are very expensive here ($300 each at the dealer) otherwise it would of course be the best to just buy a set of them and that is what will be done later on from the USA ($320+shipping)

/Jan L

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Jan, keep in mind that if you need something shipped to you in Sweden, that I would be happy to help you out, I have lots of scrap yards near me, that have injectors sitting on the shelf. Mike

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I have not done anything specific yet with my friends 90 STS but I searched the net and when reading

I experienced that there is a lot of writing about problematic injectors for the 4.5-4.9 (The Northstar injectors don't seem to be as faulty as I can understand it) and even the ECM can be the problem source. I do not have any extra ECM but I have a good set of injectors for a Mustang 90 GT which are possible to use according to different sources. The Mustang has #19 and Cad #18 and pressures are 39 psi and 43 resp. So the Cad will get some more fuel because of this but the oxy sensors

will maybe take care of this. So I think I will do a test with with those Ford spec injectors - the 4.5 runs so bad now so anything is worth trying. I also think I will advise the friend-owner to invest in an extra ECM out of Ebay (for my own 93-94 Northstars I have a couple of extra engine computers).

The idea of moving the injectors around is of course good but it will take a little more time? than just installing injectors that all work from the start - at least they did a couple of weeks ago. Injectors for the 4.5 Cad are very expensive here ($300 each at the dealer) otherwise it would of course be the best to just buy a set of them and that is what will be done later on from the USA ($320+shipping)

/Jan L

I purchased two reconditioned injectors from www.rockauto.com for my 4.5 Allante they were $27 per unit plus a $10 core charge. They worked perfectly. I did the drop cylinder test as well to determine the cylinders that were not firing. I could hear the questionable injectors fire as well as you did.

It took me some time to figure it out because it started up well cold on eight then the injectors would drop out when the engine warmed up slightly .

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Hi guys, I really appreciate the kind of help you are offering -it is especially valuable when

I need a part that is not available from for instance Rockauto where I am a customer since a couple of years. I believe that my friend will soon buy a set of injectors from Rockauto to get this job right from the beginning as his car behaves exactly like the 'blue_eldo' car. It is bad though that he can't get his 90 STS ready in time for a Caddy Tour to Germany which is taking place just in a few days - /Jan L.

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