MONTE CARLO Code 34 - 1988 Monte Carlo SS

[79 USA 1]

According to the emissions tag on my 88 SS follow the 3/16 (Letter "N' port) vacuum line from the back of the base plate on the carb to the vac sensor. I do not have access to my car right now but do believe it is mounted to a bracket that attaches under one of the intake bolts on the passenger side rear of the engine.

 

[Clone TIE Pilot]

What ground should I check? Sorry for the dumb question.

How do I erase it the code? Disconnect the battery?

The CCC harness has several grounds on the engine. One on the backside of the head and another on the waterneck bolt.


Yes, you must disconnect the battery to erase the trouble code.

 

[Clone TIE Pilot]

Oooh. You actually put in a MAP sensor in place of the BARO sensor it seems. Which is ok, they're the same sensor. So no harm done. But no fixing either. I'm not sure where the BARO sensor is on the Montes, but apparently close to the VAC sensor. You didn't do anything to fix your issue. Your VAC sensor giving you the 34 code is still in there. So if it was bad, it's still bad. Because you didn't change it.

The VAC sensor on your car looks externally the same as the BARO sensor (I'm guessing that is it) you took off, except there's a vacuum line going to the port on the bottom of the sensor, where the other end connects to the intake manifold or carburetor. Not familiar enough with the Chevys to know off the top of my head exactly where the sensors are physically located. But they do use a VAC on the V8 only. MAP on the V6. Both use the MAP/BARO sesnor as a BARO sensor only. So V6's have 2 MAPS essentially, and the V8 cars have 1 VAC sensor connected to the intake manifold vacuum, and 1 MAP/BARO (used as BARO only).

Did you do any voltage checking to see if it's acting right?

If it is indeed a MAP/BARO sensor you bought, which is what it looks like, that's likely your problem. A MAP, or Manifold Absolute Pressure, works differently than the VAC sensors. If your sensor has a vacuum hose attached to the nipple, you need a differential pressure sensor. MAP and Diff Pressure Sensors have different voltages depending on the vacuum signal. Kinda backwards from each other. This is likely your issue. At least one of your issues. Never fear, your Baro sensor is new, at least! They're the same sensor, the MAP and BARO.

Read this post.

OLDS - Olds School: 307 Olds V8 MAP sensor or MDP?

Caveat- this is mainly for Oldsmobile 307s, to which I'm more familiar with than say, the 305 Chevy engine. I believe since they use the same sensors, they work the same, but I have done absolutely no further research on them, thus, if you know something different, please correct me where I'm...

gbodyforum.com

You need the right part number ACDelco or equivalent.

View attachment 212328

Here's one on ebay. On sale. The same part number that originally came on your car. AutoZone is out of their minds trying to pass off MAP sensor as a VAC sensor. Wonder how many people have lost their hair wasting their money on that thing instead of them getting the right sensor for their Monte SS? I will SPEND YOUR MONEY HERE. Do it. This one's cheap enough. They're getting more scarce as the days go by.

AC Delco Manifold Absolute Pressure Sensor 16054920 for sale online | eBay

Find many great new & used options and get the best deals for AC Delco Manifold Absolute Pressure Sensor 16054920 at the best online prices at eBay! Free shipping for many products!

www.ebay.com

And an FE1618 by Niehoff (Repackaged Borg Warner sensor). Says MAP on the box, but it is actually a VAC. You can still see the GM logo on the sensor. Hmm. Wonder who made them for GM, Borg Warner...

Manifold Absolute Pressure Sensor-Differential Pressure Sensor Niehoff FE1618 | eBay

Niehoff FE1618 Manifold Absolute Pressure Sensor. See our other products.

www.ebay.com

Rockauto.com has Diff Pressure Sensor too.
View attachment 212329

Chevy changed the location of the Vac and Baro sensors over the years. In the later years like 88 the Vac sensor is located on a bracket on the intake manifold on top the EGR control solenoid while the Baro sensor is on the passenger side inner fender well next to the ESC module.

You have to watch out for part consolidation issues like this as bean counters don't give a damn about engineering and correct specs.

 

[69hurstolds]

Olds idiot-proofed it as best they could, then, as there's no way you can mix up the two. They separated the Baro and VAC. The V8 Vac (or MAP on V6) is on the passenger side fenderwell right on top and the Baro is in the passenger compartment by the ECM. No way to confuse that issue. In either case, your engine sensor has the vacuum tube connected to it, the Baro does not have anything connected to it.

In hindsight, GM thought they were being cute by making a MAP look like a VAC and vice-versa so they wouldn't have to redesign a new plug or mounting area. Idiots. Causes mucho confusion because when the aftermarket got involved, they called everything a MAP and figured a MAP was used for every situation. Of course, if you have a V6 and get a VAC, you'll have issues, too. I fell in that trap and called them MAPs too, regardless of what it is. I'm trying not too, but old habits die hard. Even GM called them Transducers sometimes.

GM sensors have the last 3 of the part number stamped in them right on top of where the connector plugs in. They only have 3 part numbers that work for G-body VACs anyway. Look for 920, 834, or 141. If it is any other number than those, like 832, 833, 835, etc., it's a MAP/BARO. This only works for GM sensors that I know of. I don't know about aftermarket tells.

The three different VACs that GM used are shown here:

 

[1988SS]

Thanks for all the replies.

I ordered the GM correct VAC part.....thank you 69hurstolds!!!!....hoping that takes care of my problem.

I'm a bit of a limited mechanic so I really appreciate the knowledge and the time you guys spent trying to help me out.

 

[1988SS]

I just verified the number stamped on my original VAC sensor which is 834, which corelates to PN 16006834.

I'm assuming that the 16054920 will work okay?

 

[ssn696]

The 'fee' for Forum advice is remembering to post a closeout confirmation if the problem gets solved....

 

[69hurstolds]

I just verified the number stamped on my original VAC sensor which is 834, which corelates to PN 16006834.

I'm assuming that the 16054920 will work okay?

Yes, any one of the three listed will work. The 920 or the 141 would work as well. The Borg Warner one I have that's p/n EC1618 that says MAP printed on the end flap but is listed as a VAC on their website has a 141 stamped on it.

 

[1988SS]

Update - Bad ECM

Replaced with remanufactured unit and we are back on the road.

Thanks for everyone's input.