K2500 454 with rough idle and hard starting

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Hello all,

 

I could use some help troubleshooting an idle and hard starting problem with my Chevy K2500. It has the 7.4L 454. I've only had it a few months and a few weeks after buying it I found that after it was warmed up it was difficult to start. When it was cold in the morning it would start fine but after it was warmed up and let to sit for 15 minutes or so, it would take 10 seconds of cranking to start it up and after it started you could smell fuel like it was flooded. I checked the fuel header pressure and it was at the suggested pressure. ( can't remember now how much that is, maybe 50psi?) I ran it in this condition for awhile until it threw the first code P0175 to rich on bank 2. It was suggested that the MAF sensor was bad. I replaced it and the inlet air temp sensor and now I've got a new set of problems. It is throwing P0102 pretty consitantly. I replaced the distributor, rotor and ECM but they really didn't look that bad. Today I replaced the fuel pressure regulator and I've still got the same problem. P0102 and rough idling with a hard to start problem. At one time today the fuel trim was maxed at +50% for both banks. I found that if I leave the MAF sensor disconnected, it seems to run much better but is still hard to start. After I plug the sensor back in and reset the DTC it immediately starts to idle down and right before it quits, surges up to 900RPM and then idle down again to do the same thing over and over. Is there some way to set a base line to try and trouble shoot this problem? Can I reset the computer someway?

 

Any help would be greatly appreciated.

 

Thanks in advance.

[superbee]

Do you think you might have a vacuum leak? Surging kinda sounds that way. Anyhow, when you first start and are in open loop you're okay right? Once you go to closed loop, things go to crap. I'll ask my sensor guru and see what he says. You may want to try reposting this in ask the GMtech section. Good luck

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I also noticed that the inlet air temp reads over 100F when it's 50F outside.

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Shouldn't the inlet air temp read pretty close to the outside air temp?

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Could this indicate a wiring problem with the IAT sensor?

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What is the difference between closed and open loop and how does the PCM descide to switch?

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I also noticed that it runs OK when the P0102 DTC is active and then runs bad after the DTC is reset.

[Haulin' 8.1]

There is likely a air intake leak. The code is for MAF sensor low frequincy, meaning not much air being measured but the engine is running in a manner that would require a lot of air. Your O2 are correcting the reading, hence the +% fuel trim. Look for a missing or torn boot, gasket, or component in the air intake ducting, the intake manifold, or the PCV system (crankcase included). Make sure the duct clamps are on all hose joints and tight.

 

Check the vacuum lines and the components they goto for leaks.

 

Vernon

[superbee]

Open loop is when the engine is running on it's cold preset values, closed loop is after it is warmed up it uses feedback from o2 sensors and such. That's how I understand it anyway.

[blockader09]

Air intake leak. had one just like it