OK, long story, so I'll try to keep it short.

Bought 93 STS, 91K, drove it about 5000 miles, couldn't be happier and amazed with the power. One day for no apparent reason (out of town filled up, drove hard 100ish to next town, 30 miles) developed a constant "stop light" miss, especially noticable in drive at idle. Seems to smooth at higher R but is still there. NO Codes except usual battery dissconnect, "lift and dive once", RR speed sensor, but no related.

I'm thinkin bad fuel. Changed FF and it went away for about 10-15 minutes, right back like a switch. Had plans & parts for complete tune-up including plugs, wires, systh oil, air filter, clean TB, etc. To no avail. Will go away, somtimes at cold start for a few minutes, then like a switch.

I'm getting a little frustrated by now, so I take it to the neighborhood shop for diagnosise. Couldn't use his scope(claimed it was too new) but have traced it to #1 - 180lbs compression, says it has to be injector dumping.

So I take it home pull the rail(plastic), AC/Delco test and service, five of them were 52 lean and #1 is fine. Not The Problem! must be intake gasket. replace FPR and MAP while top popped. Lifted the intake and cleaned egr passags and ratholes. They were a mess, plugged and looked like the problem for sure. Valve looked clean. Spent some time on it and reused the old gaskets with alittle orange RTV. No Good Starting to get a bit pissed by now!

Bottom line is #1 is dead, no codes, plug is fairly dry w/a slight browning of insulator at electrode, no gas smell, slight oil. Excellent spark at plug, swapped coils- no change. pretty dam sure intake is sealed good, been inside and out checking for vacum or pinched fuel, but nothing. All looks good or is new. What the Hell! NOW I AM PISSED!!! still think that hole no fuel? computer? please help...:banghead:

So...it just misses at idle and runs ok when under way or at heavy throttle...???...or does it miss all the time..??

Swap injectors between locations and see if the problem stays with the same cylinder??

Check the injector harness for continuity for injector #1........ My guess is you either have corrosion, or something (cut wire?) is causing the electrical signal from not reaching that injector. I don't recall if the ECM uses seperate drivers for the injectors, but it's possible the one for #1 is dead....

You did say that #1 is not firing, and the injectors and spark is fine, correct?

It seems to miss all the time, but it's kind of hard to tell at higher rpms, except there is a definate loss of power, throughout. It's a shaking miss at idle and a chugging miss in drive with brake. I'll go try injector swap right now and let you know.

Thanks for the fast reply bbobynski. You are the man!

I have it scheduled for the shop at 9AM tommorrow. I need my three hundred horses back!

Still hopefull I can solve this myself (with your guys help)> It has now become a mission!

That is correct Eldorado1. #1 is definately not firing. Have good spark, new plugs, wires and swapped coils to be sure with no change. ACDelco checked, cleaned and reconditioned all injectors on rail. Said they were not down over about 5% lean and not the problem. They say they're all blowing 60 now like they should.

Good point about the signal not reaching the injector I don't quite understand what you mean by ECM using seperate drivers though.

So... I'll go swap injector and check harness now and let you guys know. I appreciate your help.

One question> is it or is it not ok to start the engine with the lid off so I can check injector for clicking? "93" STS. Thanks guys....

Don't start the engine without the lid. I believe it causes the engine to rev extremely high.

To clarify, you did change plugs and wires?

Possibly the coil pack. You can switch them to see if the problem follows the pack.

Did it change with the new plugs & wires? If it got worse you may have a bad new plug. Check both on that pack.

First things first.

Swap #1 plug wire with another an see if the miss moves.
Do the same with the plug.
Take an extra plug and connect it to #1 plug wire and see if it sparks when running.

Do a Norwegian compression test. Disable the ignition and crank the motor. All beats should be even. wa-wa-wa-wa-wa-wa-wa-wa. If it is more like wa-wa-wa-WA-wa-wa-wa, That isn't one cylinder trying to fire; you have low compression in one hole no matter what the compression test showed.

Then swap injectors around and see if the miss moves.
Pull a cam cover and check for a flat cam.

Next you will need to check for a failed valve spring. It may be broken or VERY weak. It will show good compression when cranking but as the oil pressure comes up as the motor starts the hydraulic lash adjuster may hold the valve off of the seat. These can be a real bitch to find. It will most likely be an exhaust valve spring, BTW.

Good hunting

.....One question> is it or is it not ok to start the engine with the lid off so I can check injector for clicking? "93" STS. Thanks guys....

DO NOT ATTEMPT TO START THE ENGINE with the intake cover off on a 93 or 94 Northstar engine.

The cover is the top seal for the intake manifold. If you start the car with the top off, you will have a runaway/unthrottled engine!

-George

Thanks alot for all your help. Will NOT start w/cover off! Still haven't figured it out tho. Just now getting time to try the injector swap and other suggestions.

Took it to another shop this morning and they also don't have the right equipment(I guess Cadillac is the only one that does), but they were able to verify good spark and NO vacuum leak. They are guessing it is an injector software problem(1 driver per injector). Scheduled with local Cadillac Monday morn - will let you know the outcome.

They are guessing it is an injector software problem(1 driver per injector). Scheduled with local Cadillac Monday morn - will let you know the outcome.

injector software??? Wow, I didn't think it was possible for a shop to be that far off base. Then again, some of them are staffed with high school dropouts.... (<cough>..like around here... <cough>) It sounds like you've isolated the problem then..... For some reason or another, one injector isn't getting a signal. Like I said before, could be something as simple as corrosion on a connector. A wire with a nick in it can also corrode to where it will no longer conduct. Also, the ECM has transistors in it that "amplify" the signal from the actual "computer", and send it to the injectors. Those aren't serviceable, and the ECM would have to be replaced. Or I guess it's "PCM" now, isn't it....

Just out of curiosity, what makes you want to bring it to a shop? You're on the home stretch..................

You could get a noid light and see if that injector is getting a signal...