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Old 01-03-2009, 02:13 PM   #1
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Default Misfires under load, needs some input

Ok, the car started missing under load the day before yesterday. Code p0128, (engine coolant sensor). Replaced that this morning. Still missfiring underload, but not as bad. SES light flashes at me. P0300 code is present (random multiple missfires). Changed the plugs and wires, bosch wires, tr55ix plugs. I cleaned the MAF. I can ease it up to speed without any noticeable problems. If if stab it or try to push it over about 4lbs it misses and the light flashes at me. The next logical step for me is the fuel filter, any suggestions other than that?


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Old 01-03-2009, 02:22 PM   #2
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Check your fuel pressure. Changing the filter is a good idea. Giving the engine a good seafoam top clean might help as well.
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Old 01-03-2009, 03:02 PM   #3
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Here is the complete story with all the facts so I can get this resolved:

Bought the car 12/26. 88K 1 owner. Car had a half a tank of 87 octane in it, topped it off with 92. Car ran great, full boost no probs 12/28 changed oil; syntec and mobil 1 filter. Changed plugs and wires. Bosch wires and bosch platinum plus plugs (didn't know I shouldn't use the plugs). Jan 1, drove the tank almost all the way empty, added lucas fuel system cleaner and filled up with 92. 3.7 gallons into the tank, the missing started and I got an SES light. Talked to a buddy that runs a gtp 3.1 pulley, nice car. He said plugs suck and he had a set of used tr55ix, that were good when he took them out, they weren't cold enough for him, no sure how many miles on them but he said less than 1000. Changed the plugs this morning, no help. Scanned it got the p0128 (ECT) code. Changed that, p0128 went away, car runs better. Cleaned the MAF today as well. Missfires underload now, p0300. SES light flashes at me under load, the boost is 9.5. I can ease the car up to speed as long as I stay under about 4lbs seems to run fine.
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Old 01-03-2009, 09:27 PM   #4
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Have you checked to make sure you don't have a spark plug wire (#5 and #6 mainly) and make sure they are not near or touching the O2 sensor wire. This can cause error codes like this. Also check for a vac leak. These can cause misfire codes.
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Old 01-04-2009, 09:40 AM   #5
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HP Tuners showed 0 missfires on any cylinder even tho the PCM posted the P0300 code. Cylinder balances were all between 91% and 93%. Exhaust velocity/volume feels (by hand) to be good. I am going to replace the fuel filter tomorrow and put the original plug wires back on it to see what happens.

What indiciation would I have if the LIM gasket was bad? I found no evidence of oil or water pooling anywhere.

If you guys have any other ideas or info please let me know.


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Old 01-04-2009, 09:50 AM   #6
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If you have no pooling on the LIM and can smell no coolant in the exhaust and your not loosing coolant, it'* a good bet your not leaking.

As I said in the post before, check the plug wires to make sure your not touching the O2 sensor wire. Make sure none of the plug wires are grounding. Have you pulled the coils to check the contacts under them? Change the fuel filter and let us know if there'* any change. And check for any vac leaks.
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Old 01-04-2009, 09:51 AM   #7
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Quote:
Originally Posted by Danthurs View Post
If you have no pooling on the LIM and can smell no coolant in the exhaust and your not loosing coolant, it'* a good bet your not leaking.

As I said in the post before, check the plug wires to make sure your not touching the O2 sensor wire. Make sure none of the plug wires are grounding. Have you pulled the coils to check the contacts under them? Change the fuel filter and let us know if there'* any change. And check for any vac leaks.
Thanks, I will be getting that stuff done as soon as I finish my coffee and the "Zone" opens.

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Old 01-04-2009, 01:47 PM   #8
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Same thing with mine except mine is a 96 SE. Also had random misfire when trying to floor it, changed the coils, new ACDELCO plugs and wires, new thermostate, new PCV valve, cleaned MAF. Now it only misfires when the engine is cold, when it heats up to 90* degrees runs fine, now im looking at the injectors
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Old 01-04-2009, 01:52 PM   #9
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I've seen seafoam do wonders for engines. 1/3 can sucked in to a smaller vac line, the other 2/3 can in the fuel tank. Tons of smoke, runs rough for a short time, then smooths out.
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Old 01-04-2009, 01:54 PM   #10
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will it damage my new spark plugs?
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