Trouble codes 34 and 45

[Jorge6.5]

I checked for codes on my '90 Chevy k1500 with 305 since the check engine light is illuminated. The codes that came up were 34 and 45.

What do these codes mean and what could be the cause and fix for them?

The truck will sometimes have a lack of power and will buck or hesitate. The truck actually stalled twice today while going down the road. The idle can be a bit off and rough at times.

I have recently done a tune up but the truck is the same before and after. I used mostly ac delco parts, cap, rotor, plugs and wires. A new air filter and msd ignition coil. I have yet to replace the fuel filter.

Thanks guys.

 

[JiFaire]

Most likely O2 sensor (45) - rich exhaust or MAF sensor - low airflow (34)

The two are often related, as you might imagine. Look for a vacuum leak.

 

[Jorge6.5]

A vacuum leak could cause all that? I thought I heard a vacuum leak every so often. Should I chase down the vacuum leak and think about replacing the map and o2 sensor?

Thanks

 

[JiFaire]

If you have a vacuum leak, it messes with your mix ratio. You end up running rich and that in turn messes your sensors.

I'd find the leak, first. Those engines are bad for throttle plate base, intake manifold gaskets, and at that age, I wouldn't bet against cracked hoses. I had a stubby little 2" long hose leaking on my tranny (modulator valve) in an old Trans-Am ... made everything run like crap, unless I was stomping on it. Just idling around town, it hurt me for about 5 mpg. Took forever to find... I mean, who looks for vacuum leaks under the tranny?

A can of WD40 - or even ether, if you're REAL careful - will help locate any leak.

 

[Jorge6.5]

I could not find any vacuum leaks. Unfortunately i could not try the wd 40 trick cause I have none.

All hoses appear to look good. The injector spray looks ok but not great.

I heard it could be the coolant temp sensor. They are pretty cheap so I will try that next. Might even get a new map sensor while I'm at it .

Will post my results.

 

[JiFaire]

Look up the codes online

www.gmtuners.com/OBD1_DTC.htm

GM OBD-1 Diagnostic Trouble Codes. For 1995-previous model year EFI- equipped GM vehicles.

this list says 34 is vac high... Mine said MAF low. One way or hhe other, I'm betting you have a rich condition affecting your o2 sensor. Did you clear your codes after changing the air filter?

 

[Jorge6.5]

I'm not sure how to clear the codes on OBD I. The check engine light isn't always on. I scanned for codes while light was off and got nothing.

The truck runs good at first then it bucks the light comes on and the power is kinds weak.

 

[Jorge6.5]

Well I picked up a new coolant temp sensor, replaced that and now I'm only getting code 34. While driving the ses light will go out and come back on several times. Still have lots of bucking, hesitation and lots of fuel consumption. The truck sometimes feels like its ready to die and has stalled today at a red light. Come Friday I'm gonna replace the fuel filter that I've had for it, recheck all vacuum lines and connections. Might just go ahead and replace the map sensor. Also read someone was having a code 34 and turned out to be the ECM. The carb swap is looking like a much better idea at this point

 

[WarWagon]

The sensors and ECM are cheap vs. a carburetor. TBI is stupid simple. Codes don't mean much as the computers report the symptom, value out of range, not the problem. This code is saying the MAP voltage is low: High vacuum. May be an electrical problem. MAP is also the baro sensor and can start you at the wrong altitude so the entire time the engine is running it is lean or rich due to thinking it is at an altitude it isn't at. The ECM reads the MAP as a Baro sensor at start-up before engine cranks, WOT, and maybe another condition I forget about.

May be a true high vacuum situation. Throttle body worn or out of adjustment. IAC sticking or gummed up.

Clean the MAP sensor connector and trace wires including our favorite trans dipstick ground.

Can't disagree with simply tossing a MAP at it, but, I would check the TB for groves/wear, the IAC, and maybe run a TBI adjustment procedure first.

Disconnect batteries for 30 seconds clears codes. Get it over 45MPH to allow the ECM to re-learn the IAC position by the ECM stepping it 255 times closed.