backfire at 15lbs of boost

[blackazz]

Morning to all the gurus here in GN world my ? Is I'm out driving my car an gave alil gas an boost an at 15lbs of boost my gn back fires an if I put my foot in its azz at 15lbs its surgging. What could this be?

 

[mygn276]

Your lean.

 

[1fast6]

lean, just got to find out why. i had that issue at 19# and up. turned out to be my maf....

 

[just plain john]

Can you monitor fuel pressure when under boost? Fuel pressure should rise one pound with a boost increase of one pound. If base fuel pressure is 40, with 15 pounds of boost you should have 55 pounds of fuel pressure. Until you can verify this you're just guessing.

 

[blackazz]

Thanks guys for the input ill check my m.a.f an my fuel pressure is mounted on the rail lookin into hood mount style now

 

[Frank87gn]

Also check your spark plug wires, you may have a cable loose. So when you're normal driving is fine, but when you get into high boost it will back fire. This is what happened to me a few weeks ago. Hope this helps.

 

[LI6pack]

Same problem

I have an 87 with about 30k on her. Just did a complete tune, wires, plugs and fuel filter included. Car runs a bunch better but stiill backfries a little and I'm afraid to punch it. I did get a replcement MAF a few years back from Kirban. I'll check the wires again but what else should i check out?

 

[1fast6]

I have an 87 with about 30k on her. Just did a complete tune, wires, plugs and fuel filter included. Car runs a bunch better but stiill backfries a little and I'm afraid to punch it. I did get a replcement MAF a few years back from Kirban. I'll check the wires again but what else should i check out?

Do you have a scan master?
need to check fuel pressure...

 

[turbojd]

Check all ground wires, make sure they are tight, check coilpack also. Also check the cam sensor ring and make sure it's still pinned to shaft.

 

[LI6pack]

I don't fast, just really starting playing again since my kid turned 16. Pulled out of the garage, change the TCC, water pump and tuned her up and have these little. squawks. I know w good guy here in NY though and i will have him check that out.

I have an old fule press reg on it, think it was a dutwiler one (blue) with an old applied technologies chip. The guy i know said they 2 have to go, lol. He has a new chip and new FPR in stock

 

[LI6pack]

thanks Turbojd. What do i check on the coil pack? Where is the cam sensor ring, sorry for the non mechanically inclined questions.

 

[turbojd]

thanks Turbojd. What do i check on the coil pack? Where is the cam sensor ring, sorry for the non mechanically inclined questions.

You can ohm out the coilpack with a voltmeter, front to back, should be between 11k-13k ohms. You have to take the cam censor cap off and you will see the tab, make sure it did not loosen up.

 

[blackazz]

crank sensor maybe ?

Ok guys sounds like a lot of input to go thru but I jumped out the frying pan into the fire cause I went from a unstable idle to a back fire an for the tab on the cam sensor can't tell if it broke the ring so unscrewed ring cap tab still good,wires pluugs coil all showing good by chance could this be something with the crank sensor the reason I ask mine came lose an was cracked by the H/B so I replaced it I set it to .10 sound right

 

[1fast6]

How To's

There are two things to note when installing a new crank sensor

do you have a scanmaster or power logger? can you post up your readings at idle with engine at operating temp?

 

[turbojd]

Set the crank sensor at .025, when you do this, check all 3 interuptor blades for proper clearance. Make sure the sensor is not rubbing anywhere.

 

[tzque]

I had all of the same problems and spent to much money . Please make sure the hose on the back of the turbo has not come off or now has a whole in it . Check your lines before you buy parts .

 

[Frank87gn]

Another thing that may cause backfire is the module. This is underneath the coil pack. This happened to my brother, he replaced and no more backfire. Hope this helps.

 

[frank700]

I chased this same problem. Did everything mentioned above. I was getting a knock/backfire 15 pounds and up. Turned out to be a vacuum leak. Yes that was it. Too rich. Car runs incredible now. Get a vacuum pump. The one with a gauge on it used for bleeding brakes. Pull off the lines on top of the dog house. See if they hold vacuum. The line running to the boost/map sensor and the back of my autometer boost gauge leaked. Very simple fix. I believe a lot of people have leaks and don't know about them. Good luck!

 

[GNRick]

Also check the tps sensor. With key on (car off) depress it with your fingers while monitoring voltage. If there is a dead spot where it reads -0- volts, you need a new sensor. A bad sensor caused my car to blow off the up pipe. Huge backfire!

 

[blackazz]

vac leak behind turbo

Ok guys after searching an searching found the problem vac leak running now last time I drove this car was 07/09 been a long time coming new tran monster in a box rebuild w/pro hog torque 3200 stall an all I can say is O.M.G. I missed these cars he is a sample of the scanmaster#s everything look ok too you guys?
Af 04
Lb 21
Int 148
Bl 160
Clt 193
Ats 128
Rpm holding 800-850
Tps 44
Iac 24
Cc 21