1995 Firebird Low RPM shaking / missing

I have a 1995 Firebird w/ a 3.4L engine. Recently, I changed the spark plugs on the car with Bosch (new plug, no gap required). After the plug change the car started running horribly bad (missing). The car misses after shifting into overdrive (at very low RPM) - severe shaking. I changed from the Bosch new fangled to Autolite platinum plugs and replaced the wires. The car ran well for about 5 minutes, then started shaking again.

What could be the problem?

  m5racerx

hmmmm tough one... when you had the plugs out did you check the compression, go back to basics and check the three main things... spark(which you hprobably have) fuel(pressure test and volume test) and air(is it getting enough and does it have proper compression?) if all turns out well i would start with ignition diagnostics. check all the wiring test the sensors, make sure all the inputs to the ignition module are fine, if you wanna guess and throw parts at it like most people, start with new sensors crank or cam or both then go coil packs then ignition module... guessing gets expensive by the way

  BanffAutoSpa_ap

what did the old plugs look like? deposits, discoloration, etc.

  dodger65

Take out your plugs and gap'em to 0.060" and put a little dielectric grease on the boots of the wires(both ends)...make sure the wires snap on securely to both the plugs and the coil pack. Just because spark plugs are new doesn't mean you shouldn't still check the gap(unless it's a bosch+2 or +4 in which case you really can't gap'em)...many spark plug part numbers fit multiple applications, each usually requiring a different gap setting than others. Basically...the spark plugs in your car are designed to work in a few different applications. Try what I said, and let me know what happens...start off with simple easy things then work your way up....also, make sure you have your firing order right...i've seen that done many times.

-Don

  Sick88Tbird

Spark plugs looked fine, no oil or gas or other unusual deposits.

  m5racerx

OK, I can try this new gap setting, but the mfg recommended setting is 0.045".

  m5racerx

The misfiring is getting worse over time. It used to be that at higher RPMs the car would run relatively normal; however, after driving it a few days, the car is running progressively worse. It is as if the plugs are fouling...

  m5racerx

if it says .045 go .045 your stock ignition probably cant handle more than that effectively

  BanffAutoSpa_ap

all the plug wires are on the right plugs, right? (sorry--gotta ask) and are you aware that #1 on that motor is on the passenger front?

  dodger65

undefined :thumbs:

Plug wires are all in the right places (yes I am aware of plug 1 position). As I said previously, after working on the car, cleaning the plugs, etc. it starts to run better. However, over time (1 or 2 days), it appears that due to whatever is going on with the car, the plugs start to "foul" up and the missing progressively worsens.

I'm sure someone else has seen the same issue, but so far, no such luck...

  m5racerx

I'm having exactly the same problem with the same car and engine. Anyone have any ideas on this yet?

I've changed plugs and wires and I'm wondering if it's the fuel injectors? Any thoughts?

Thanks,

Mike

  coach mike

Maybe somethings wrong with your distriburator?

  vmc2

Ive said it once and Ill say it again: Its the Bosch plugs. The dont work for shit in American cars for some reason. :screwy: Replace them with Autolites, and youll have no more problems.

  SlipKnoT

get some ac delco plugs best plugs you can get.

  adamc44

Autolites always tend to work better in Ford products. And AC Delcos for GM cars.

  SlipKnoT

I have new AC plugs and wires but the problem still is there. What else should I be looking for?

  coach mike

injectors not firing? you might be able to pick up a noid light from a parts store and test the wiring going to the injectors, if the all fire then you should make sure the injectors are working fine,a couple of ways of doing this, the best is a waveform viewer with a low amp probe so you can watch the solenoid windings and the spike of current....without the low amp probe??? hmmm maybe pull them out and see if the fuel spray pattern is proper, i dunno lol good luck, just buy 6 new ones and throw em in ;)

  BanffAutoSpa_ap

It doesn't sound like the problem is the plugs. The new plugs fouling are probably only due to the engine running poorly.
A quick easy way to check for a really bad injector is to pull the plug wires one at a time on each cylinder. If the engine idles worse while pulling one then the injector is probably ok. If the engine runs the same when pulling one then the injector is probably bad. Note; if an injector is only slightly bad then it might be hard to tell this way.
Check over the new plug wires and make sure they did not come into contact with something like the exhaust manifold. Maybe do an ohm test on them. Should be around 6000 ohm give or take about 1000 ohm. I'm not familiar with your car but if the distributor has any sensors on/in it and you replaced/removed the cap you might check that (optic sensors and dirt/oil, not good). Also check the interior of the cap and the rotor, even if its new.
Maybe check the coil.
Make sure you did not disturb any of the connections on parts when you installed the plug wires such as on the following: Injectors, TPS, MAF, IAC, O2 sensor, Temp sensors etc.. Also, make sure the connectors are clean. A corroded connector that got bumped could have gone out completely.

Finally, maybe the ecm has locked up, try undoing the battery terminal for a few minutes and then reinstall it (who knows)!!!
Go into some more detail: You said it ran good for five minutes then ran bad. Is this always the case (that would tell us it starts when the engine gets hot). Or does it sometime run bad immediately upon startup (when the engine is cold). Does it run bad all the time or just sometimes? When it running bad does it clear up at times or is it consistant? What does it do at higher rpms (like 40 to 50 mph)? Was anything else done to the engine? The more information you give us the more likely we can help you solve the problem. Good Luck!

  Macc

Thanks Macc. I'll check the things you listed. Actually on mine, occasionally has a hard time starting when hot and really spits and sputters under those conditions. I put some fuel injector cleaner in last week and didn't drive it until this morning - letting it sit over the weekend after putting about 200 miles last week with the cleaner going through basically. It seemed a little better but still a hard start this morning.

I appreciate the input guys.

Mike

  coach mike

Here are some additional thoughts.

On some electronic fire ignition engines there is a ecm(computer) relay. If there is a problem with the relay it can shut down or affect parts such as the ecm, injectors, fuel pump, maf etc. and cause engine problems. So, search for such a relay and check its condition.

On many engines a single fuse may be for several different sensors (such as the o2 sensor, the IAC etc.). If that fuse is bad or corroded then the sensors will not work properly and the ecm will read it as one or more bad sensors and likely cause the engine to run bad. Check over the fuse panel.

In one of your posts you said that the car ran ok for about 5 minutes then began to shake (this sounded like it started when the car warmed up). The EGR Valve comes into operation once the engine is warm to hot. Sometimes is can stick open or have a poor seal and flood the intake with exhaust.

Finally, the o2 sensor measures the leftover gas in the exhaust. If there is too much it tells the ecu to cut back on fuel. If it is acting up it can cause engine problems. But, if it completly goes then the default it for the ecu to send more fuel. So, take a quick smell of the exhaust and see if it smells like gas or rotten eggs. This would indicate a shot o2 sensor.

Good luck!

  Macc

You need hotter plugs by the sounds of it.

  Wally