as the title says im having engine issues and im running lean, thought it was a vacuum leak but my vac pressure gauge stays put at 14 psi which according to my instructions is spot on for being 7500ft above sea level. all the open and closed throttle tests came back negative for anything. cant be a vacuum leak so now im leaning toward bad fuel pressure. anything else that you guys can chime in on would be appreciated.

 

Your spot on with assuming fuel psi. Rent, borrow, buy a fuel psi checker and see what you before throwing any parts at it.

 

Yes it can be a vacuum leak...it only take a small amount of unmetered air to trigger a lean condition. It would have to be a HUGE leak to show up on a vacuum gauge.

I highly recommend checking the fuel pressure as noted above AND running the Key On Engine Off (KOEO) tests and stored code (CM) display.

 

ive done the KOEO and engine running tests. ive gotten 18, 22, 33, and 41. 33 i know isnt a problem because ive removed the vacuum solenoid to the egr valve and its stuck closed. 18 is my timing (i removed the distributor and didnt mark it so got it pretty damn close if you ask me and ran great for a month until this issue. 22 is something to do with the map sensor and obviously 41 is a system lean.......im starting to think that maybe it could be an air leak with the map sensor going out of range.......any more advice? i wont be able to get to a fuel pressure gauge for a couple days. ordered my own since i cant take time off work to go loan one

 

Code 18 (CM): IDM circuit failure

Has nothing to do with the base timing. IDM=Ignition Diagnostic Monitor. This is an engine RPM signal to the computer. It uses a 22K ohm resistor to buffer the coil On signal from the Ignition Control Module.


Code 22(KOEO/CM): MAP sensor out of self test range

There is the most likely culprit of all your issues.


Code 41(CM): HEGO sensor circuit indicates system lean

As previously noted for the MAP sensor code.



The computer relies heavily on the MAP sensor to determine how much fuel to apply to the engine. Inaccurate feedback from that signal causes all kinds of issues.

Verify the output with a DVM that can measure frequency. I picked up a $22 USD cheapie at Harbor Freight years ago, works great for this application.

For reference: MAP Sensor

 

i will test the map sensor. also will crossfire cause these same issues? the misfire and lean condition?

 

Misfire, yes......lean condition, not very likely.

 

okay. also another update. when i run the truck to operating temperature then shut her down for like 5 minutes then turn it back on it runs like a champ. no misfire or anything. idk what that could mean. it does it every time

 

another update.....sprayed starting fluid all over the plenum, hit every vacuum line, the vacuum tree and nothing. also when at idle if i unplug the map sensor the engine runs amazingly other than a slight increase in rpms

 

Did you test the MAP sensor?

 

wasnt able to. my voltmeter cant test frequency i dont think

 

i ordered a new map sensor. standard motor red box. im pretty darn sure its the map sensor. everything else that ive tested using my voltmeter has been good. fuel pressure was good at 40 psi.

 

40 PSI under what conditions? At idle with the vacuum hose attached? If so, that's too high. Should be in the 30-34 PSI range.

 

sorry mine was at 36 psi at idle. but when i prime the fuel pump its at 39 or 40. waiting on my new map sensor to see what it does. also i decided to test the iac valve for ****s and giggles and when i unplug the connector the idle only goes down like 100 rpms. could this actually be the problem?

 

Yes that is a problem. Has nothing to do with your MAP code.

Either someone has jacked with the Idle Stop screw or you have a vacuum leak. Look at the stop screw, it should have thread locker on it. Verify the lock has not been cracked or other disturbed by someone moving it.

If it looks untouched then you have a vacuum leak.