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Old 07-12-2013   #1
Louvers
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Could use some help, please.

Hi everyone. I am having some issues with my '92 and I wanted to see if you all could help.

Over last month or so my '92 with a 5.7 started acting up. It acts like it's misfiring on one cylinder. I took it to a local shop and they found bad plug wires and a distributor issue. I had all the wires, cap, distributor and O2 sensor replaced but it's still acting up. The mechanic is now saying I need to replace the injectors but I don't really trust him anymore.

Basically, at startup the car runs great. Idle is smooth and so is the acceleration. The issue starts as soon as the car gets warmed up. When you come to a stop and then accelerate again, it sputters and acts like it wants to stall. It's also sputtering now at high speeds which it wasn't dong before I had all the items above replaced.

I'm about an hour from Hawks Third Gen and I'm considering taking it to them now. I wanted to get some thoughts from you guys here first as to what you think might be going on.

Any help would be greatly appreciated. Thanks,

Darrell
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Old 07-12-2013   #2
merc3065
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Re: Could use some help, please.

Fuel pressure is at what PSI? Can you get an external gauge and hook it up while the car is in motion and observe?

This could be a failing fuel pump or fubar'd injectors since you've replaced all of the spark side.

Get a PSI check on the fuel rails and see what it's at.
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Old 07-12-2013   #3
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Re: Could use some help, please.

Quote:
Originally Posted by merc3065 View Post
Fuel pressure is at what PSI? Can you get an external gauge and hook it up while the car is in motion and observe?

This could be a failing fuel pump or fubar'd injectors since you've replaced all of the spark side.

Get a PSI check on the fuel rails and see what it's at.
The mechanic did say the fuel pressure was low but within spec. I believe he said it was at 39 psi. Unfortunately I'm not much of a mechanic. I just don't want to go into extreme expense here by continuing to replace items until the problem is found.

If I had a bad injector, would the car still run fine when cold and then start to run rough as it warms up? Or, is this more likely a fuel pressure issue?

Also, any ideas of what it should cost to replace the injectors by a mechanic? His quote was high, like $1200.
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Old 07-12-2013   #4
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Re: Could use some help, please.

When my fuel pump went, the symptoms started suddenly. One day it ran great, the next day it was hard to start and ran poorly at start up but gradually ran better as it warmed, as some fuel pressure slowly came up (apparently). But, I have heard that some pumps just flat out quit and did not slowly die like mine. Your symptoms seem to be the reverse of mine. But, if your FP slowly bleeds away when the car warms the injectors may not be functioning optimally.
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Old 07-12-2013   #5
Big&Bad89GTA
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Re: Could use some help, please.

Check your fuel injectors with an ohm meter. If you have one "bad" injector, it will feel like a misfire. Two injectors, it really feels goofy... More than two, it might not start, especially once it warms up...
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Old 07-14-2013   #6
Louvers
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Re: Could use some help, please.

Thanks everyone for the input. I will likely just bite the bullet and replace the fuel pump and the injectors.
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Old 07-14-2013   #7
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Re: Could use some help, please.

Something not mentioned yet would be your MAP sensor. That along with my injectors starting to fail gave me the same symptoms you seem to be having. The sensor is easy to replace and it can cure the problem temporarily (it at least got me home in a pinch), but it does sound like injectors for the most part. Test them like was mentioned and you could even put a scope on each injector to listen to it. A good injector will have a definitive pulsing sound where a bad one will sound like its got a blanket on it or no pulsing sound at all. Replacing them isn't as bad as it looks even if you took extra time, it's something that can be done in a day.
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Old 07-15-2013   #8
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Re: Could use some help, please.

Ohmeter on the injectors, should be 16 ohms when cold.
If they are out of spec, they need to be replaced.

Fuel pressure should be at 42psi with vacuum disconnected. 39 is low and could cause the fuel to sprinkle vs atomize nicely which could indicate that you may have a leaking injector or a fuel pump on it's way out.

When injectors heat up through normal use they could stick open. It's electronic so it could happen.

Check the spark plugs as well. They should look light golden brown. If they are wet, black, or any other colour than a light golden brown, it can point to what's wrong.
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Old 07-16-2013   #9
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Re: Could use some help, please.

If the injs are stock and haven't been replace I'd put my money on them.
The fuel PSI seems a tad low but ok.
As stated above, OHM check injs when car is cold and then warm.
If you haven't, change the fuel filter.
Bruce is a good guy and can help out.
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