Bucking boost

[andrew4g63]

My car has a bad problem that i have not been able to fix. When I first start it up it runs great, then i go drive around and it boosts normal, then if i shut the car off and restart it the car will not rev over 3000-3500, The boost will stick at 3-4psi and not go down till i coast with no gas for a while, Then as soon as i press the gas the car shoots black smoke and bucks from the boosting problem. I fixed all the boost leaks also, any ideas would be greatful Also car is stock A/T with 14b and 450's

 

[huafist]

My car has a bad problem that i have not been able to fix. When I first start it up it runs great, then i go drive around and it boosts normal, then if i shut the car off and restart it the car will not rev over 3000-3500, The boost will stick at 3-4psi and not go down till i coast with no gas for a while, Then as soon as i press the gas the car shoots black smoke and bucks from the boosting problem. I fixed all the boost leaks also, any ideas would be greatful Also car is stock A/T with 14b and 450's

Did you replace the ECU when you added the 450's or do you have an AFC? If not, there's your culprit.

 

[andrew4g63]

no it has a M/T ecu not the culprit

 

[slickndual87]

Mine started shooting black smoke out, which was the fuel, all I did was change the o2 and it was fixed about 10 miles later.

 

[ddavisaf]

Is there a CEL present? If so, what is the code for?
What kind of spark plugs are in the vehicle?
What is telling you your boost is sticking at 3-4 psi? The stock gauge, or an aftermarket one?
If stock, inspect the ECU for leaking capacitors.

 

[andrew4g63]

No CEL's It has NGK BPR7ES and Accel wires, the stock boost gauge
Ill put a aftermarket one in today and see what it says

 

[laserspeeddemon]

yea, my stock boost gauge says I run 11 psi, while my after market one says 15+psi. The stock one is worthless. And most likely you are hitting fuel cut due to a boost leak.

Did you test PCV?
Did you test EGR?
Did you test Valve Seals?
Did you test TB seals?

When you boost leak test it should hold over 15 psi.

 

[andrew4g63]

It has a new PCV, No EGR, how would I test valve seals, Brand New Throttle body Seals
Im going to put the aftermarket gauge in right now and take it for a ride keep you guys updated

 

[ddavisaf]

yea, my stock boost gauge says I run 11 psi, while my after market one says 15+psi. The stock one is worthless. And most likely you are hitting fuel cut due to a boost leak.

Did you test PCV?
Did you test EGR?
Did you test Valve Seals?
Did you test TB seals?

When you boost leak test it should hold over 15 psi.

You want to hold 20 psi for 30 seconds or more.

 

[danyz250f]

Do you want to hold 20 psi for 30 seconds then start to bleed out or do you want it to take 30 sec to completly bleed out all the pressure from 20 psi.

 

[laserspeeddemon]

... how would I test valve seals,...

A boost leak tester, set the timing mark on the harmonic dampner (cranshaft pulley) to about 12 o' clock. Pressurize the intake tract, remove the oil cap and listen into the valve cover, a hissing from there can indicate a leak at both the PCV or the valve seals. If you want to be EXTRA sure that its not the PCV, then remove and plug the hose from the PCV. And listen again.

BTW a boost gauge is required to do a correct boost leak test.

 

[andrew4g63]

^^^^^^I try that today

 

[andrew4g63]

Put a Boost Gauge in today and it says its not sticking like factory but car will boost at 1500 rpm and stock gauge stays at 7 psi or so. So is this a ECU problem (capacitors) maybe? Also black smoke is shooting out so I am going to put the 390's in it maybe for some reason the ECU is not realy a M/T. Did not try valve seal test yet

 

[huafist]

The factory boost gauge doesn't actually read boost; it displays what the ECU thinks boost SHOULD be based on calculations done on airflow and load. That's why you upgrade to an aftermarket gauge, they're not accurate at all.

The black smoke is a sign of a rich condition. Could be that the ECU is compensating for the wrong injectors, or a myriad of other problems - we need more information. Fix your boost leaks so the gauge will hold 20psi, then go from there. Post the MD and E2T numbers from the ECU casing and we can cross-reference them.

 

[andrew4g63]

ECU number is MD166262 i checked it at vfaq alreadly. I also put a boost gauge in today and drove around and it was reading like it should, car was still shooting grey smoke and not going over 3000rpm. I shut the car off for 10 min and then was going to drive it back home when it drove normal, no boost problems. I drove around for about a half an hour and then drove though a parking lot with speed bumps at the end of the lot the car started it boost and sputtering problem.

 

[andrew4g63]

Fixed was bad ECU