Hi,
I own a 94 Camaro V6 3.4l and had/have issues with a misfiring engine. When it first occurred a mechanic installed new spark plugs and replaced the ignition wire set. After that the engine was running perfect no misfiring and definitely more power than before. So I was very happy, well until about 2 weeks later. While driving on the highway the engine went suddenly from perfect to misfiring really bad. Back to the shop. They found wires and plugs were still fine, but there was no output by cylinders #2, 3, and 4. But #1, 2, and 5 had good output. Compression was at 125 psi.
I had to decline the recommended replacement of all 6 fuel injectors since the cost estimate was about 2k, which is more than the car is worth. One mechanic mentioned that maybe bad fuel could have caused the 3 injectors to fail and recommended filling up with high octane fuel to “clean out” the injectors- is that a possibility/ good idea?
Thanks a bunch,
Chris
High octane gas isn’t going to solve the problem.
A compression test reveals the condition of the engine. If some cylinders read good compression, but others are low it usually means the engine is worn out and either needs to be rebuilt or replaced.
Or the timing chain may be stretched.
Tester
Whether or not the problem truly lies with the fuel injectors and how they failed is easily determined with a good scan tool, some test equipment, and accurate data while the engine is running. Whatever the problem, the octane of the fuel won’t help anything.
I’d expect 6 new injectors installed to be under $1500.
Bad gas could be the cause. Does this car have a gas filter??? If so when was the last time it was replaced???
What you might be able to do is pull the injectors and clean them. Soak them in fuel injector cleaner. I’ve never done this…but I know a mechanic who’s done it…says it works great.
Based on this information, I doubt that the problem is fuel injectors, but yes, poor fuel can gunk up fuel injectors, and the injectors used by GM in those days were fairly sensitive to fuel quality. I am not familiar with your particular engine, but generally, removing fuel injectors is only a little more work work than removing spark plugs.
If the problem is fuel injectors, adding different fuel or pouring fuel injector cleaner (e.g. Techron) into the tank is not going to help at this point. Some mechanics pull them out and others pump cleaner through them in place, but the best approach is to take them to someone who will ultrasonically clean them and check the flow and spray pattern. Witchhunter and Cruzin Performance do this via mail order in about a week if no one locally does it. I doubt that new injectors are called for, though that is the quickest and most profitable course of action for your mechanic.
Cars have been equipped with Fuel filters for many, many years…Injected cars have a large, high-quality filter…But if you never change it, and it fails, it can dump its contents into the injectors, destroying them…
New injectors are available on e-Bay for a fraction of dealership prices…$2000 is an insane price, even at dealership parts and labor rates…A mechanic who has done this a few times should be able to do this in under two hours…
Dont’ spend any more money. The 125 PSI of compression flat sucks so you have serious engine problems more than likely.
When the shop found 125 PSI they should have immediately run a wet compression test to determine if the rings are gone or the problem is in the valves. It’s likely the former.
Given the shop doesn’t know that 125 is bad then I would question the injector diagnosis as well.
The fact that your car was running fine after the plugs & wires were replaced, but then suddenly started to misfire 2 weeks later is a big clue. It is unlikely something that has been building up for a long time. Here’s what I’d do if it were my car, in order:
- This is most likely an electrical firing problem. First thing to do is check all the high voltage electrical connections (the spark plug wires and the common wire going to the distributor cap), and if nothing noted, then replace the the distributor cap. Inexpensive.
- To rule out injector problems, test the fuel injectors for equal fuel output. Don’t do this yourself unless you have expertise on fuel injection systems and their maintenance. Good mechanics know how to do this; they just pop the injectors, insert them in separate test tubes, and run them all for 5-10 seconds simultaneously, then they measure to see that all test tubes contain an equal volume of gasoline. It doesn’t take much time to do the test, so it shouldn’t cost more than $200 or so for that.
- To rule out compression problems, test each cylinder. They should all have more or less the same compression. “OK” says 125 is a low compression, I don’t know whether it is or not, but it is unlikely all the cylinders would go from good to bad compression at once. If they all measure more or less the same, compression isn’t the problem. A compression test takes less time than the fuel injector test.
- If you still haven’t figured it out at this point, your problem is probably some problem in the electronic ignition system. You could try simply replacing the coil if you wanted to take a gamble. You’ll probably need to find a mechanic who has specific expertise on your car to fix it at this point.
Thanks a lot for all your replies. My favorite answer is definitely the one from George_San_Jose not only because he gives me at least some hope that there is a chance to fix the car without going bankrupt but also because I think I can rule out most other possibilities:
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the fuel filter has been replaced twice over the last 3 years (once on purpose and once “by accident”) plus the last time I filled up before the engine started misfiring was at brand name gas station, so most likely it wasn’t the fuel then.
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the car has only 130,000 miles, I am the 2nd owner and the 1st owner really took care of this car, so even considering that it’s a Chevy I don’t think the engine should be seriously worn out already. Well, but I don’t know what the compression (psi) should be . . .
-Anyway the car ran flawlessly until the misfiring occurred the first time, except for the fact that you had to crank the engine 2-3 to start when cold. So I am thinking that’s maybe another hint for an electrical problem - as George_San_Hose suggested.
BTW all of you were right, high octane gas and injector cleaners did not help at all. So I will try the distributor cap + rotor next.
Thanks,
Chris
I’m surprised they didn’t change the cap and rotor when they did the wires.
Cap and rotor are generally supposed to be replaced more often than the wires.
It could be the compression test wasn’t done properly (throttle open?) or the gauge is off.
The compression readings are low, no ifs, ands, or buts about it. This test should be revisited and done properly the next time.
I will add that when compression gets low like this that misfires are going to develop as low compression like this can start killing off spark plugs.
Can an engine run at least apparently well with compression this low? Yes. The question is how long and and would it be worthwhile to sink money into a problematic motor.
Given the low compression, the failure to recognize that basic problem, and a stratospheric price on a set of injectors I would not rely on this shop too much.
(I’ll also add that some service manuals refer to compression readings like 125 being fine and so on. Well, those manuals are dead wrong. They were written by technical people with no clue and compression readings like this are not the only flaws to be found in the specifications section.)
Today, a “Compression Test” performed with a mechanical gauge inserted in a spark-plug hole is a rare thing…Most shops use the “electronic” method today and some of this diagnostic equipment will even fabricate PSI readings based on RPM drops as the cylinders are shorted out…
When you pay for a compression test, ask if it will be done with a mechanical gauge or not…
Wow! I must say I’m flabbergasted at my recent problem with my 98 BMW 540i…
I have a 98 BMW 540i with 305k on it now. I bought the car with 290k and I must say have been really pleased with the way it runs until now. It started missing so I went to Autozone and after they connected a “box” to diagnose it, they told me number 7 was missing due to either a plug, coil or injector. I swapped coils with number 6, replaced the plug and went back to have the box hooked up again—still number 7. I put Techron in to no avail. Here’s what crazy to me: it started out smooth at idle then missing, then smooth again cycling in this manner. It would miss when I would accelerate and drive it. It progressed from those characteristics to steadily missing for a good while and now seems to come and go but is more prevalent than not. So it’s back to missing while idling but when I accelerate sometimes it doesn’t miss and sometimes it goes back to steadily missing!
Dumbfounded…
Thank you all in advance.
Thanks again, and yes I won’t go back to this dealership they are really expensive and you can only talk to the guy at the counter but not to the mechanic itself, I am sure there is a better place in the East Bay area.
Anyway I was getting ready to buy a new distributor cap for my car- Autozone cells one for a Camaro 3.4l 1994 - but then I found out my from the manual that my car has none! The 3.4L engine uses a “waste spark” method of spark distribution . . . - not sure what they sell at Autozone then 
Well, so I will replace the ignition coils - seems to be not too expensive and doable - and if that doesn’t help I’ll try to find a good, honest and approachable mechanic to figure out what’s wrong.
-Chris
So what are you going to do after spending a fortune replacing every single engine performance part on that car and then “discover” that the engine has serious issues: as in the 125 compression?