Just new here.
my 90 eldo 4.5 just decided to develope a miss or 2 just after the dealer did a tune up. The gm tecks did a balance test and thought it may be a head gasket. I stripped the engine down and did a compression test All cyl were at around 160 - 180 except for #-6 which was 110 I put some carb cleaner into the injector port and gave it another test and compr. was up to 160. i suspected a dirty valve. The vehicke will start but decides to miss on # 8 and then on #6 and #5 . I can rev up in idle, but when in gear, it misses badly and no pwer at all OF COURSE.
I have no va*** to the brakes and not enough va*** to activte the park brake release. Brake is very hard as if it was not running.
My Question: Could it bea plugged Cat or bad injectors.
Prior to this event, I had it through air care and it failed the Nox , no engine miss and the HCO and Co were very very low. The car ran very well prior to this. It never used oil and there is no water in the pan and no bubbling in the rad when it runs. This led me to belive it was not a head gasket. ANYONE have ANy ideas. Any comment is welcome.

Thanks
Denny

as soon as you said that something went wrong after they worked on it, that was all i needed to see..go back and make them fix it...if it was fine before the service, and bad after it was worked on, they fouled something up...

Did some more checking and it is missing on 8, 3, 5, and #2 cyl.
NEW: plugs, cap, rotor, and wires check out ok at 10,000 ohms or less.
Can the electronic controll module cause this eratic behaviour??

How do I check the pick-up coil in the dist.??? Anyone have specs
Thanks
Denny

Up date:: fuse was blown for 1 bank of injectors. Miss not as bad, but still runs rough.
Set code e041 and replaced cam sensor/helix and now code is history.

Next I checked injectors for resistance and I had 3 bad ones. Replaced them and car runs great.
Injectors read at 15 - 16 ohms and 3 of them were below 6 ohms. What a difference. They must have been going bad for a while because for 3 years my nox readings were climbing even after I put in a new cat.

Hope this helps someone

Up date:: fuse was blown for 1 bank of injectors. Miss not as bad, but still runs rough.
Set code e041 and replaced cam sensor/helix and now code is history.

Next I checked injectors for resistance and I had 3 bad ones. Replaced them and car runs great.
Injectors read at 15 - 16 ohms and 3 of them were below 6 ohms. What a difference. They must have been going bad for a while because for 3 years my nox readings were climbing even after I put in a new cat.

Hope this helps someone

Well, got the care to pass emmisions.
Problem originaly___ bad hall effect and 4 injectors below resistance that was acceptable.
Then I failed emissions and checked the egr tubes at base of intake and they were plugged. Cleaned them out and nox went down to new vehicle specs.
Only problem now is a fast idle on deceleration. Tps and isc reset and all within specs, but idle stays high (1400 rpm) cruising at 25 - 30 mph. Have to use brakes and at 5 mph, it shifts down hard and idle settles down to 750 rpm as it should. Any one had this problem??

thanks
Denny

not much to say but i have the same problem with my 90 deville... i have replaced fuel pump, filter, plugs, wires, and the distributor.... and still the same problem as urs..... i havent tried the fuel injectors yet..... how did u test them....

What does the emgine have for a base idle ? These motors will see any vaccuum leak as increased idle speed. If it has a good base idle I would be concerned with it's learned minimum air rate. You can reset that by unhooking the battery and losing the old learned idle speed. Rehook the battery and start the car w/o touching the throttle, if it stalls at first that's OK. Let it idle for 10 minutes. SHut it off and restart again and let it idle in gear for 10 minutes. This may resolve your idle issues.