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Old 11-08-2013, 07:24   #1
w30olds
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Car fellows. Got a question for you

I have an older 95 Grand Prix 3.1L. It has a brand new crate motor. New plugs, wires, coils. It's ran flawless for the first 2500 miles. Tuesday out of the blue it started running really awful. I'm smelling gas and it has awful power. Took it back to the mechanic. He had it for 2 days and couldn't seem to find the problem. He said it might be a bad fuel injector on the #1 cylinder. The check engine light does not come on at all. I was wondering if anyone has had this issue and is it a common problem? I'm going to take it to another repair shop and have them check for any codes in the computer to see if it is something like a sensor. Jus wondering if anyone else has had a fuel injector go bad on them before and what sort of symptoms did you have?

Thanks!


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Old 11-08-2013, 07:29   #2
tehan2
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without a scan it's hard to narrow these things down.

That said, I'm not familiar with the GM 3.1 but it sounds like a vacuum leak of some type
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Old 11-08-2013, 07:32   #3
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Vacuum leak, bad injector, faulty sensor........hard to tell.
Get it to a shop that has the ability to run a diagnostic scan.
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Old 11-08-2013, 07:33   #4
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If your mechanic cannot troubleshoot a bad injector, he's not qualified to do an oil change.

If you do have a "bad" (leaking) injector, that new motor is getting the rings washed with gas and ruining the new motor.

Pulling the codes won't tell you what is wrong, it just tells you what symptoms are present that the computer is aware of.
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Old 11-08-2013, 07:41   #5
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Thanks guys. The car is at another shop and they are going to look at it. I don't want to drive it and risk a fire or tearing up the new engine. The mechanic that installed the engine looked at it and I think he just didn't want to mess with it any longer. Makes me angry that he kept the car for 2 days and couldn't find the problem. Will not be going back there anymore to say the least.


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Old 11-08-2013, 07:44   #6
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I'm not 100% certain if GM still used this system in '95 but I've seen a couple go on '91-'92 GM 3.1 engines. The injectors are run in a batch order meaning if one goes bad, it makes all of them go out and just dump fuel. The engine won't rev up past a low RPM like 2500 with very light throttle input only. Anything over 1/4 or 1/2 throttle and the engine chokes out. Black smoke will be coming from the exhaust.

If that is your case, you have to check each injector's resistance to find which injector is bad and unplug it. Or just unplug and replug each injector one at a time while it's running. Your intake manifold may not allow access to do this without disassembly like the one's I had to mess with. When the bad injector is unplugged, the rest will work properly and the engine will rev up normally again albeit with a slight miss due to being down one cylinder.

Good luck to you.
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Old 11-08-2013, 07:50   #7
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#1. Find a better mechanic.

What he "thinks" is wrong with your car can easily be checked out & confirmed. Why did he not do this? Any mechanic worth his salt could easily perform an injector test using very basic hand tools in less than 5 minutes (as long as the injector is accessible easily as yours is).

Most competent shops would have an exhaust gas analyzer that would tell them if the engine is running rich or lean. Heck most modern scanners have the ability to monitor the fuel tables/values. Some scanners even have the ability to test individual injectors through the software. Simple.

Again, whatever reason you have chosen that specific mechanic is turning out to be a poor reason. Find another reputable shop/mechanic that has the ability to properly & accurately diagnose the vehicle.

The flip side of this coin is that there is a chance that the shop CAN verify the problem but wanted to charge you some diagnostic fees to do so and maybe you did not want to pay, or did not have the cash to pay these fees. If that is the case.. Well, time is money. Time the mechanic spends chasing down problems is time that he, or the shop, needs to be compensated for. Most customers do not want to pay to have a car diagnosed-they only want to pay to have it repaired. Just so you know-in most cases more time is spent diagnosing a repair than actually performing a repair. It's not fair to the shop to spend 2 hours chasing down a problem, performing multiple tests to actually confirm where the issue is, then only replace a $30 sensor and then have the customer expect to pay only for the sensor. Sorry, it does not work that way.

Some shops simply won't spend the time necessary to drill down on the actual problem. They will just guess as to what the problem is and sell you a part based on that guess. Then, when that does not fix it, and you bring it back for the same initial complaint, they will guess again and sell you a 2nd part.. You see where this is going right? Yes, they may initially seem to be cheaper because they did not charge you for diagnostic time to actually solve the problem.. But if you add up the # of times you had to come back, the lost personal time, and the number of parts they end up selling you hoping to hit on the actual problem, you will see that this is a losers proposition.

Find a GOOD shop that will be able to accurately diagnose the problem through testing of components, and then sell you the part, or service, that will actually solve the problem. Yes, you can expect to pay 2 hours (+/-) in diagnostic fees but if it solves your problem the first time without replacing parts that are not bad is that not worth it? I think so.

You say you have no codes setting at this time and the check engine light is not coming on. If you do a couple more key starts, the PCM may set a code. Key starts are simply starting the engine, shutting off the key, and starting it again. Often times the PCM will not set a code until it has seen the same problem during several (3 or more) key-starts before it will set the code. Take several short trips with it and see if it will set the code. Also, take the vehicle to Auto Zone or some other place that will scan it for you for FREE. YOU need to know what the codes are and if any are being stored. Maybe it is setting a code and your shops scanner is just not picking it up. Otherwise, find a shop with a good scanner that can view the fuel tables to see if it is running rich, or lean..
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Old 11-08-2013, 07:53   #8
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Quote:
Originally Posted by jfost11 View Post
I'm not 100% certain if GM still used this system in '95 but I've seen a couple go on '91-'92 GM 3.1 engines. The injectors are run in a batch order meaning if one goes bad, it makes all of them go out and just dump fuel. The engine won't rev up past a low RPM like 2500 with very light throttle input only. Anything over 1/4 or 1/2 throttle and the engine chokes out. Black smoke will be coming from the exhaust.

If that is your case, you have to check each injector's resistance to find which injector is bad and unplug it. Or just unplug and replug each injector one at a time while it's running. Your intake manifold may not allow access to do this without disassembly like the one's I had to mess with. When the bad injector is unplugged, the rest will work properly and the engine will rev up normally again albeit with a slight miss due to being down one cylinder.

Good luck to you.
Thanks sir for the info. The car idles badly. Misfires like crazy when driving. At first I thought it was ignition related but that was ruled out by the previous mechanic. He was pretty sure that it was the #1 cylinder that could have a bad injector. Hopefully this shop has better mechanics and can find the problem.


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Old 11-08-2013, 07:56   #9
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Quote:
Originally Posted by w30olds View Post
I have an older 95 Grand Prix 3.1L. It has a brand new crate motor. New plugs, wires, coils. It's ran flawless for the first 2500 miles. Tuesday out of the blue it started running really awful. I'm smelling gas and it has awful power. Took it back to the mechanic. He had it for 2 days and couldn't seem to find the problem. He said it might be a bad fuel injector on the #1 cylinder. The check engine light does not come on at all. I was wondering if anyone has had this issue and is it a common problem? I'm going to take it to another repair shop and have them check for any codes in the computer to see if it is something like a sensor. Jus wondering if anyone else has had a fuel injector go bad on them before and what sort of symptoms did you have?

Thanks!


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Not necessarily a "car guy" but I will give this a shot:

If you have a faulty injector then you should have a misfire on that cylinder. Try disconnecting the #1 plug wire and see if the engine runs any different. You can go through the sequence 1-6 and if a cylinder is "dead" it should show up as no change in how the engine runs.

If you track down the dead cylinder, wiggle the wire to see if it starts to run better. Sometimes the spark plug wires will "ground out" due to rubbing on a part of the engine and rubbing a hole in the insulation. It is very hard to get all of those wires routed back just like they were.

However, I don't think crate motors come with the top end or the "optispark" system. Those have been known to go bad.

Also, no check engine light typically means no trouble codes.
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Old 11-08-2013, 08:07   #10
w30olds
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Quote:
Originally Posted by Kawabuggy View Post
#1. Find a better mechanic.

What he "thinks" is wrong with your car can easily be checked out & confirmed. Why did he not do this? Any mechanic worth his salt could easily perform an injector test using very basic hand tools in less than 5 minutes (as long as the injector is accessible easily as yours is).

Most competent shops would have an exhaust gas analyzer that would tell them if the engine is running rich or lean. Heck most modern scanners have the ability to monitor the fuel tables/values. Some scanners even have the ability to test individual injectors through the software. Simple.

Again, whatever reason you have chosen that specific mechanic is turning out to be a poor reason. Find another reputable shop/mechanic that has the ability to properly & accurately diagnose the vehicle.

The flip side of this coin is that there is a chance that the shop CAN verify the problem but wanted to charge you some diagnostic fees to do so and maybe you did not want to pay, or did not have the cash to pay these fees. If that is the case.. Well, time is money. Time the mechanic spends chasing down problems is time that he, or the shop, needs to be compensated for. Most customers do not want to pay to have a car diagnosed-they only want to pay to have it repaired. Just so you know-in most cases more time is spent diagnosing a repair than actually performing a repair. It's not fair to the shop to spend 2 hours chasing down a problem, performing multiple tests to actually confirm where the issue is, then only replace a $30 sensor and then have the customer expect to pay only for the sensor. Sorry, it does not work that way.

Some shops simply won't spend the time necessary to drill down on the actual problem. They will just guess as to what the problem is and sell you a part based on that guess. Then, when that does not fix it, and you bring it back for the same initial complaint, they will guess again and sell you a 2nd part.. You see where this is going right? Yes, they may initially seem to be cheaper because they did not charge you for diagnostic time to actually solve the problem.. But if you add up the # of times you had to come back, the lost personal time, and the number of parts they end up selling you hoping to hit on the actual problem, you will see that this is a losers proposition.

Find a GOOD shop that will be able to accurately diagnose the problem through testing of components, and then sell you the part, or service, that will actually solve the problem. Yes, you can expect to pay 2 hours (+/-) in diagnostic fees but if it solves your problem the first time without replacing parts that are not bad is that not worth it? I think so.

You say you have no codes setting at this time and the check engine light is not coming on. If you do a couple more key starts, the PCM may set a code. Key starts are simply starting the engine, shutting off the key, and starting it again. Often times the PCM will not set a code until it has seen the same problem during several (3 or more) key-starts before it will set the code. Take several short trips with it and see if it will set the code. Also, take the vehicle to Auto Zone or some other place that will scan it for you for FREE. YOU need to know what the codes are and if any are being stored. Maybe it is setting a code and your shops scanner is just not picking it up. Otherwise, find a shop with a good scanner that can view the fuel tables to see if it is running rich, or lean..
I totally agree with you. I don't have any problem paying for a good shop to run the tests. At least they will know what the issue is and not guess at it, or just be parts changers. So many shops seem to want to guess at the problem and not actually verify it with a scanner, or diagnostic tests. I'm all onboard with them doing the tests and finding the problem the first time.


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Goodness and Mercy shall follow me all the days of my life. I shall dwell in the house of the Lord forever.
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Old 11-08-2013, 08:14   #11
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It could be as simple as the little 1/8" vacuum line to the fuel pressure regulator is cracked or disconnected.

Pulling codes won't tell you the problem, it will tell you symptoms of the problem that the mechanic must use to troubleshoot the likely causes of said symptoms.
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Old 11-08-2013, 10:10   #12
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Elsolo hit a home run with his post. So many people & shops rely on codes to tell them what the problem is when in reality you should only be using the codes as a base line starting point for your diagnostics. Many customers believe that a scanner exists that you can just plug in and it will spit out what part needs to be changed. Some of you are laughing, but many people actually believe this is how it works.

Good post Elsolo.
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