OBD code 34

[kickdeez]

I have been getting intermittent misfires and hesitation/stumbling over the past couple weeks. Problem seems to occur when the SES light is on. The light does not come on all the time...maybe once every 4 or 5 times I start the truck. When the light is off, the motor runs fine, no issues, no stumbling or misfiring. When the light is on, it is throwing a code 34, which I understand to mean low circuit voltage to the MAP sensor. I read somewhere along the way that I should check the vacuum hose from the intake manifold to the sensor. I have decided that I am just going to replace all the vacuum lines, as they generally appear pretty aged, so I went ahead and ordered some new silicone vacuum hose. In the meantime, can someone send me a picture of what the MAP sensor looks like and where it is located? Also, my knowledge of this issue is very limited, and any troubleshooting suggestions would be much appreciated. The fact that it is intermittent makes me think it may be an electrical issue versus a leaky vacuum line. If it was a leaky vacuum line, I feel like the problem would be present all the time. What else should I look at or consider? 1990 GMC Suburban with 454 tbi. Thanks in advance!

Also, not sure if I posted this in the correct section (maybe Electrical?). If it's in the wrong spot, I apologize, and please feel free to move it to the correct section.

Kyle

 

[89Suburban]

Here is pic of the MAP on my 1990 Burbs 350 TBI in the yellow circle. My '89 had it mounted on the bracket in the orange circle.

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[kickdeez]

Your picture does not show up for me for some reason...

 

[bucket]

It could just be a bad MAP sensor if the vacuum lines are good. It could also be the EGR valve sticking open causing an intermittent vacuum leak. When it is running properly, you can disconnect and plug the vacuum line going to the EGR valve, then drive it around like that for a few days. It will likely set an EGR code at some point, but if it doesn't act up then you have narrowed it down to a sticking EGR.

Also could be a leaking TBI mounting gasket, I've seen them intermittently leak.

 

[kickdeez]

Well a leaking tbi gasket should be fairly easy to identify with a can carb cleaner. And as far as that goes, I guess I could check the vacuum lines that way too. I will give that a try and report back. I hate to just start blindly throwing parts at it. Is there a way to test the MAP sensor to tell if it is bad?

 

[89Suburban]

Your picture does not show up for me for some reason...

Fixed it, sorry about that got pulled away from the computer.

Here is a thread that may help:

http://www.gmsquarebody.com/forum/showthread.php?t=8719

 

[kickdeez]

Thanks for the picture and the information. I checked for vacuum leaks last night with a can of carb cleaner and did not find any. I did see that the clip on the plug from the wire harness to the MAP sensor was broken off. I didn't think it would be a big deal because the plug was still connected; however, when I started fiddling with the plug while it was running, I was able to replicate the stumbling and poor idle symptoms I have been experiencing. The SES light also came on. When I squeezed the plug tight into the MAP sensor, the symptoms and the light went away. I did this several more times to confirm it wasn't just coincidence. I have ordered a new pigtail connector from RockAuto and it should be here in a few days, along with the new silicone vacuum lines I already ordered. When they come in, I'll splice in the new connector and install the new vacuum lines, then I'll report back. Thanks for the help guys.

 

[kickdeez]

I got the new vacuum lines installed and spliced in the new map sensor connector. I took the truck for a spin and it ran fine. No stumbling or missing during the drive. I got back to the house and turned the truck off. I started it back up to head back out, and when I got the the bottom of the driveway, the motor died out. It appears that the injectors are not spraying. There are no warning lights on the dash. The fuel pump kicks on when I turn the key into the on position. What would cause the injectors to not spray?

 

[kickdeez]

Fixed it. It was a bad ignition control module. Don't know why it would be bad, the whole distributor (and whole ignition system for that matter) is pretty much new within the last 2,000 miles. But it was definitely the culprit. Swapped in the new ICM and it fired right up.

 

[bucket]

I've seen the ICMs crap out after 20 miles before.