Why can't I boost higher than 12 psi??

[rocketron]

I've tried several different 3 bar calibrations that are supposed to boost to 18 psi but I can never boost over about 12 psi. As an experiment I tried using a manual boost control device and found that I have no problem going as high as 21 psi (afraid to try any higher). So...why do I have no problem boosting as high as I want with a manual device, but when I leave it up to the ECU to control the wastegate, it won't le me go higher than 12 psi!!??

[Twisted Noodle]

There are others on here that will probably have a lot more knowledge about this than I.

I would look at the hardware that the computer controls to adjust boost. After checking ALL my vac lines (including the one from the brake booster to the back of the intake manifold) and zip tying all of them (I had a similar problem at 12 lbs) I would look at the solenoid. I know you said you went up to 21psi with a MBC but if you had a leak somewhere in the lines you might have been running much higher than the gauge was reading.

[minigts]

Why are you using the computer to control it? I'm not sure I see the point in using the vacuum solenoid.

[turbovanman²]

The stock setup can be made to work but most times, you'll be bashing your head against a wall. Just leave the MBC hooked up and adjust to your desired boost level.

[turbo84voyager]

The stock setup can be made to work but most times, you'll be bashing your head against a wall. Just leave the MBC hooked up and adjust to your desired boost level.

I agree. I never set the boost settings in my cals I use a MBC on everything.

[rocketron]

I totally destroyed my last engine with detonation and I'm trying to be cautious this time and figure out how it happened. The engine showed signs of prolonged detonation, one of the pistons had its rings broken into many pieces and all the bearings were smashed to pieces and literally crumbled apart when I took the engine apart.

I don't really understand how the automatic boost control system works so I'm just wondering if there is a reason why the ECU won't allow full boost, and whether I should be figuring this out rather than ignore it by bypassing it with a manual boost control device. I do know that the ECU will retard timing if it senses detonation but can it also limit boost if it senses detonation or other problems?

[turbovanman²]

I totally destroyed my last engine with detonation and I'm trying to be cautious this time and figure out how it happened. The engine showed signs of prolonged detonation, one of the pistons had its rings broken into many pieces and all the bearings were smashed to pieces and literally crumbled apart when I took the engine apart.

I don't really understand how the automatic boost control system works so I'm just wondering if there is a reason why the ECU won't allow full boost, and whether I should be figuring this out rather than ignore it by bypassing it with a manual boost control device. I do know that the ECU will retard timing if it senses detonation but can it also limit boost if it senses detonation or other problems?

The stock computer won't pull boost if it sense's detonation, the only thing it does is pull timing.

Its tedious to make the stock boost control work with a bunch of add on's, hence why 90% of us use an MBC or EBC as they are rock solid and reliable. If you turn the boost up slowly, you won't damage anything.

What mods do you have and what gauges?

[ShelGame]

I don't really understand how the automatic boost control system works so I'm just wondering if there is a reason why the ECU won't allow full boost, and whether I should be figuring this out rather than ignore it by bypassing it with a manual boost control device. I do know that the ECU will retard timing if it senses detonation but can it also limit boost if it senses detonation or other problems?

It depends. If your cal is based on the '89T2 or earlier, then no. It won't reduce the boost due to detonation. But, from the '89 2.5 T1 and all later cals will change the WG duty cycle if there is detonation detected. It won't reduce the boost 'target' so to speak, but it will effectively lower the boost by closing the solenoid. It's a short term correction, though, so if you get low boost due to that, you must have a ton of detonation...

[rocketron]

I have an 89 t2 setup.

I was totally stupid, I didn't have any gauges or anything (except for a dawes device which I guess is not very reliable since it never told me that there was any problem). Now along with my new engine I have a wideband O2, an EGT sensor, and an AFPR. But, in my defence, I had a custom calibration (Paul V) and I wanted to the computer to control the boost so I wasn't pushing my luck. But since it wouldn't go higher than about 12 psi on its own, I added a manual boost device as an "experiment" and a couple weeks later, blown up engine!

I just remembered something else to add. When I tried putting the stock injectors, map and a Mopar Performance Computer in the car, it boosted to 14psi, just like it's supposed to. But with the 3 bar cal (in fact I have two different ones from different calibrators) both calibrations rated for 18 psi max out at around 12 psi.

[turbovanman²]

I have an 89 t2 setup.

I was totally stupid, I didn't have any gauges or anything (except for a dawes device which I guess is not very reliable since it never told me that there was any problem). Now along with my new engine I have a wideband O2, an EGT sensor, and an AFPR. But, in my defence, I had a custom calibration (Paul V) and I wanted to the computer to control the boost so I wasn't pushing my luck. But since it wouldn't go higher than about 12 psi on its own, I added a manual boost device as an "experiment" and a couple weeks later, blown up engine!

I just remembered something else to add. When I tried putting the stock injectors, map and a Mopar Performance Computer in the car, it boosted to 14psi, just like it's supposed to. But with the 3 bar cal (in fact I have two different ones from different calibrators) both calibrations rated for 18 psi max out at around 12 psi.

Nothing wrong with a Dawes, if you pay attention to it at WOT, you can't do any damage if you have the right gas and no knock.

As for an MBC, you can only blow sh*t up if you go too crazy without using your brain, like I tend to do,

I honestly would just stick with an MBC and be done with it, why pull your hair out over something so trivial.

[rocketron]

Anyone else agree/disagree with Turbovanman that I stop worrying about why my setup won't boost automatically and just use a manual control device?

[ShelGame]

My guess is that you're running a 2.5 and the computer boost control doesn't work because your custom cals are based on the '89 T2 which uses a different style of boost control compared to the T2 (T1 uses a bleed style). If you want the computer boost control to work, it has to be plumbed appropriate to the style of boost control being used. Maybe try re-plumbing your boost control like the T2 (complete with restrictors-they're important!)...