p1188

[Dalite]

Well, the TIP sensor modification is a bust for time being. I removed the sensor from my GT and tried to take resistance readings and note changes when pressure is applied.

I found that the resistance leads (1 and 3) are definately polarity sensitive. I get different readings when the leads are reversed. The center lead (wiper; the one that is grounded) shows about the same when measured against 1 or 3, not very affected by polarity.

This suggests that there is more inside the sensor than a simple pressure operated variable resistance, as the wiring diagram suggests.

I am not currently set up to apply 5 volts and ground to the sensor and then make checks of the output voltage under varying pressure. I should be able to make those tests by the end of the month, when we get back from vacation and things settle back down.

I took a peek under an "inspection port" on the TIP sensor and saw 5 contacts; even though the sensor connector only has 3. I suspect that the resistance leads have something as simple as a diode to only allow current flow in one direction, or as complicated as an opto-isolator or an opamp. This is only speculation.

I don't suggest trying to dissassemble the sensor. As it is, I had to re-seal mine, and I won't know for a few hundred miles if I caused any new problems with my curiosity.

[PETEY_CRUISER]

I know this may sound very far out there but could it be the simple fact of the hoses use for the turbo going in to the throttle body can only take so much pressure before they expand.In wich we are push them past their tolerances causing expantion. If so this may cause the "spike being seen". If this is the cause then the surging air would set off TIP reading as the pressure jumps up and down at the throttle body as the hose ballons the contracts making eratic pressures faster then an boost gauge would pick them up, but can be seen buy the ECU. The best way to check this is to find some one whom has replayed the rubber hoses with manderal bend piping. Something I will be doing in the future any ways.

[OurPTGT]

YOU GUYS ROCK! [?] I don't understand a bit of it but do appreciate the efforts you guys are putting forth and thank you all for it![|)]

[dgc333]

Guys I would like to make a couple of comments, I may be off base here (I have not got my service manuals yet) but it's based on my 18 years of 2.2 turbo mopar experince.

1. The waste gate solinoid does not vent to reduce boost. It applies pressure to the wastegate actuator to over come the spring and open the waste gate. The vent on this solinoid is to let the pressure back out of the wastegate actuator quickly. Where it gets it's pressure source from is pretty irrelevent. You could supply it with a can of pressured air and not have connected to the engine at all. They likely choose to hook it up right at the output of the turbo becuase that would be the point with the highest pressure (no loss due to cooling or velocity loss).

2. The TIP I believe is an absolute pressure sensor, that is, it measures both boost, vacuum and the output will vary with cahnges in atmospheric pressure. It's connected to a solinoid so the ECM can vent it to atmospher periodically. This happens to let the ECM know if the car is going up a mountain side of if the has been a dramatic change in atmospheric pressure due to a front.

3. My experience has been when you make changes to the exhaust and or intake that will allow the turbo to spool faster you can get into a situation that the rest of the system can't keep up and you will see boost spikes. The length of the lines, the diameter of the lines even the speed of the solinoid can come into play here. I would seriously doubt that changes in tube diameter due to expansion from slightly higher pressure is the reason. The hose expanded enough to impact that you would also have issues with them blowing off there fittings.

4. I have no clue about the programing in the PT but it would not suprise me that the system is monitoring the TIP sensor and making comparisions to throttle postion and rpm to determine what the boost should be allowed to rise too. By putting a boost controller in line you have changed the boost mapping and the computer is simpley setting the code because it does not agree with what it expects. Most of the high boost 2.2 cars have a zener diode across the MAP sensor (TIP) that limits the output voltage so the ECM belives that the car is operating at a lower boost level. The sensor will act normally below the zener value.

5. I am also suprised that you guys have not taken a cheap power tip from the 2.2 guys. You can make a boost controller from a simple pressure check vale that you can get for $5 from a hardware supply house (i.e., the infamous "Grainger Valve").

[Dalite]

quote:Originally posted by dgc333

Guys I would like to make a couple of comments, I may be off base here (I have not got my service manuals yet) but it's based on my 18 years of 2.2 turbo mopar experince.

1. The waste gate solinoid does not vent to reduce boost. It applies pressure to the wastegate actuator to over come the spring and open the waste gate. The vent on this solinoid is to let the pressure back out of the wastegate actuator quickly. Where it gets it's pressure source from is pretty irrelevent. You could supply it with a can of pressured air and not have connected to the engine at all. They likely choose to hook it up right at the output of the turbo becuase that would be the point with the highest pressure (no loss due to cooling or velocity loss).

Technically correct. When the wastegate opens, exhaust is diverted from the turbo directly to the exhaust system, and the turbo starts to spool down with the loss of exhaust gas turning it. When the wastegate is closed, the exhuast gas is directed through the turbo allowing it to create boost. Whether it is boost pressure that is vented, or exhaust gas that is used to build boost, the result is the same.

quote:
2. The TIP I believe is an absolute pressure sensor, that is, it measures both boost, vacuum and the output will vary with cahnges in atmospheric pressure. It's connected to a solinoid so the ECM can vent it to atmospher periodically. This happens to let the ECM know if the car is going up a mountain side of if the has been a dramatic change in atmospheric pressure due to a front.

[i]The TIP is Throttle Inlet Pressure. The emission control diagram at the front engine compartment, above the grille gives a simple schematic diagram of the vacuum system. The TIP gets it's pressure from the top of the intake mainfold. In that respect, it does adjust for altitude compensation, as it sees air from the charge air cooling system that is conditioned by the inter-cooler (the service manual states that the increased air flow to the engine provides altitude compensator also). The Manifold Absolute Pressure sensor is at the front left side of the intake manifold (I think this is the correct location). It is fed from the same line that feeds the brake booster, with vacuum blocked with what the diagram shows as vacuum ejectors. The TIP does see both Vaccum and pressure.. The TIP is the source of the p1188 error that keeps popping up. It does report back to the PCM, and the PCM controls the solenoid that vents the pressure it sees, on command.

It is a theory that the TIP tells the PCM to send the command to the Wastegate Solenoid to start venting boost, by diverting the exhaust gas spinning the turbine, whenever the PCM sees the RPMs start to hit the powerband and approach the 5500 RPM mark. By reducing the boost and momentum of the turbine, the PCM sets the system up for a shift, without the turbine trying to keep spinning at top speed when the RPMs start to drop for the shift. Same deal with getting off the gas. A real BOV would eliminate part of this need for anticipation by the PCM. The end result is that the wastegate and the Surge Valve Actuator Solenoids vent both the input to the turbo and the compressed intake gas at the output of the turbo. This aids greatly in preventing the turbo shaft from trying to asorbe the stress of a suddden loss of turbine RPM, by relieving both ends of the system.

When the manual boost controller (valve, fish tank areator control, grainger valve, vernier pressure valve with vent) changes the low end of the boost pressure, the TIP sends a message to the PCM that the Wastegate Solenoid isn't doing it's job, as

[dgc333]

I have the coupon from the owners manual to order the FSM set. I guess I will have to get off my duff and get it ordered so I can bone up on the new systems. Maybe I will throw my laptop on the seat and hook up to the OBDII port and drive around and log some data.

BTW, I noticed you mention the "5500 rpm mark" my car is very consistant at WOT shifting at 6000rpm. I think my first mod will be to add a boost gauge.

[Dalite]

On the 5500 rpm benchmark... It has been used as a benchmark for the 2.4l in the past, and I have gotten used to it. It may have changed on the Turbo. Past 2.4L dyno results have verified that even though the redline and revlimiter threshold are higher than this, 5500 seems to be the point that HP increase seems to flatline. The Jet and other vendor chips have tried to address the highend RPM to HP ratio, and I don't know the final outcome. One of the favorite dismissals of the performance chips by vendors that choose to not carry them is that the only performance benefit is achieved at or near redline.

I would be extremely interested in finding the source for logging software and info on purchasing or hombrewing an interface to allow a laptop to connect to and log from the diagnostic port. I haven't done this since playing with an 85 Camaro some years back with a logging setup. Do you have a source you could recommend for the setup?

Adding a boost gauge is a real eye-opener, and a partial disappointment. It is a key item in trying to understand what Chrysler had in mind in the way it handles boost on the GT. They include the gauge as a stock item on the SRT-4, and apparently are real proud of it. Cost to order a replacement is around $156.00. I am running a cheap mechanical one that is velcroed to the dash in front of the driver's side dash speaker. I hooked a twist tie through the grille and wrapped it around the hose inlet, then added the velcro on the front edge. I am planning to get an autometer pod and some decent gagues. Plans now are to get a good boost gauge, EGT gauge, and possibly the Dawes Devices A/F LED indicator setup.

If you are looking to monitor A/F on the GT, you will have to add in an additional sensor. The one(s) that Chrysler uses on the GT are wideband, heated and biased at 2.5v. Dawes recommends to use a sensor from a 91 Shadow to feed the .1 to 1v standard A/F gauges.

[dgc333]

This guy http://www.obd-2.com/ makes a pregnant snake adapter cable that interfaces the OBDII interface to an RS232 port on a PC. You can down load his software from the web site.

I purchased the universal cable from him that has the transciever chips to interface all three of the interface protocols. The SAE standard requires the manufactures to support a standard compliment of codes. This guy provides seperate files with manufacturer specific codes so you get the defintion as well as the code for those too.

He updates the software on a regular basis and is pretty good about support via email.

I will either wait for the A/F manufacturers to start selling one specific to the 2.5 volt range or modify one to work.

There is nothing special about a 91 Shadow O2 sensor, they are all the same except for length of wire, connector and whether they are 1, 3 or 4 wire.

[Dalite]

Thanks for the info. I am off to that site after this reply.

The 91 Shadow sensor was just a recomendation as a general low price sensor to use with the Dawes Devices LED box that they sell to monitor A/F ratio. You are right; nothing special, just a suggestion for a cheap sensor that should be readily available to do the job with the stock gauges.

I would like to see someone come up with an A/F gauge that makes use of the wideband O2 Sensors that the GT uses. Better still, would be an interface that piggybacks with the diagnostic connector or PCM connectors to output info to a gauge driver that would allow extraction of any monitored system's information. Someone could make a mint on this kind of interface, and custom gauges that would be compatible. Probably just a pipe dream, but I did mention it as a "want list" to one of the Kenne Bell guys on another forum.

Again, thanks for the info!

[Exhaust Depot]

The P1188 code triggers when the car sees X amount of boost with only the throttle being partially open. I would hit fuel cut on my car when at a low RPM and i get on the gas half open. THe boost would shoot up very fast even thouhg you have the throttle partially open.

Stock boost on teh srt is about 11-12. I got the message at only 12 psi with my boost controller. The controller makes boost come on sooner.

I will be experimenting by putting a T fitting on the sensor so it can bleed off some of the boost so it sees less pressure on it.