P1188 Code

[Gear_Head]

I recieved this in an E-Mail and was asked to share it with those on this forum by Mike Dalton:

I have been reading the forum about the P1188 code. The forum is not
allowing new people to join so, I couldn't answer by the way of the
forum. After trying many different things, I finally found one the
works. Would you please pass it on to other boost controller buddies
without the stage 1 and who is only running a boost controller.

I noticed a transducer on the firewall that checks for a vacuum and
boost source at the throttle plate. I took the small vacuum line off the throttle body hose and put a one way vacuum valve between the small hose and the large throttle body hose. The transducer sees the vacuum but no boost. If you look, Chrysler uses these one way valves all over their vacuum lines too keep the boost away from any source that only wants to see a vacuum. I had an old valve that was used on one of my old Mopars to keep the heat vents from changing when you stepped on the gas. I have had this on for two months and no codes at all. I used to get the code 3 to 4 times a week.
I tried leaving the hose off and tried putting in a small orifice so the computer would see some boost, but they didn't work.
I found out the computer only wanted to see a difference at the throttle plate, but didn't like part throttle boost. It now sees a negative 22 inches of vacuum and 0 atmosphere. Works great.
Thanks for passing this on.
Mike

[TripleJackInGA]

That's cool beans! I'll have to have a look at my car to see if I can tell exactly what he's talking about.I've been wanting to run a MBC for some time, but didn't want to waste the time if I got the codes.

Thanks!

[Cal Cruzer]

Boy if he had some pics that would be cool.
I wonder why he couln't join the board here?

[COP TZER]

The big hose he is talking about is the one that runs from the I/C to the T/B. It's about 2 1/4" in diameter. There are two lines running to it, an electrical sensor and a vacuum line. The black vacuum line is what he is talking about...i'm gonna try this for sure, once the snow goes away!!!

[RODRUN]

Is this not the hose that PTDave and myself have talked about and got no no's from people when we talked about the pull you get when you block it off. If you run stage 1 and do that mod you do not get the code anyway.
I want one of those valves though.

[amx1397]

If you remember "18 LBS BOOST AND NO CODE" I have been running 18 lbs of boost for the last 8 months with out a eng lite.look at the past post.

[Jason_L]

This isn't just the TIP line is it? If so, I don't see how the checkvalve could be any different then just pulling it?

[RODRUN]

Hey Gear Head, can you get some pictures?? Or part numbers?

[Dalite]

To effectively eliminate the p1188 code, DCX needs to incorporate both a BARO and TIP sensor - and not rely on a solenoid and excess hose to switch a single sensor between both duties.

Putting in a pressure-reject or vacuum reject check-valve would solve the overall code throwing part of the problem, but would eliminate half of the data that the PCM is anticiating from the stock one, and this may result in performance inconsistency.

Your friend's fix is a good fix to eliminate the code, and indicates a good deal of thought went into it.

The problem seems to come from the fact that the sensor is toggled between duties of Barometric pressure (when not under boost) and Throttle Inlet Pressure (When under boost).

It is a mechanical re-routing of pressure/vacuum that is achieved electrically by it's associated solenoid (on the passenger firewall) that is the root of the problem.

The time delay created by the closing of solenoid contact and the difference in time for a change from pressure to vacuum or vice-versa was apparently not factored into the PCM programming, it becomes confused when it sees pressure and is anticipating vacuum (or vacuum when it is anticipating boost).

Adding a MBC further complicates this with additional hose and a bleed valve. They both introduce additional time delays.