Noob needing help, not building boost and backfire

[jhef83]

I'd also check fuel pressure. Running lean will cause a backfire.

 

[QUIP'6']

i would also suspect the coil pack/module

 

[wile2k]

AF
TPS
IAC
BL

Grab the numbers in park @ idle and motor at full temp.

Coil Tower Resistance
(measure front to back, on top) 11K - 13K ohms
(for each of the 3 towers)

Thanks Rick,

Key on / Warm Idle

AF 04 / 05
TPS .44 / .46
IAC 140 / 10
BL 128 / 110

All Scanmaster readings
L8 00 / 38-41
BAT 12.2 / 13.8
INT 128 / 128
MPH 0 / 0
CLT 148 / 162
ATS 113 / 110
R 0 / 775-850
CC 0 / 25
PL 3.5 / 1.6
SP 0 / 28.1

Having a volt/ohm meter brought to me, do I just measure between the two leads on each coil?

Thanks again for the help.

 

[wile2k]

Passenger side 12.82k ohms
Center 12.65k ohms
Drivers side 12.75k ohms

 

[TurboBuRick]

Passenger side 12.82k ohms
Center 12.65k ohms
Drivers side 12.75k ohms

I had to go for a ride before it rains, sorry for the shrot delay.
That looks ok on the ohm test but that does'nt meen the module is not causing a miss. Only thing I notice is your BL is running a little low (110). That means the ECM is taking a bit of fuel out for some reason. But not a whole lot. I would be curious what BL # is aproaching the problem area (RPM) and during.

 

[TurboBuRick]

O ya, TPS is a little high. I shoot for 40 on the scanmaster because when compared to direct scan it seems to run 2 digits high. Thats not contributing to you problem though. Just a little fine tuning.

 

[wile2k]

I had to go for a ride before it rains, sorry for the shrot delay.
That looks ok on the ohm test but that does'nt meen the module is not causing a miss. Only thing I notice is your BL is running a little low (110). That means the ECM is taking a bit of fuel out for some reason. But not a whole lot. I would be curious what BL # is aproaching the problem area (RPM) and during.

I can go for a drive and find that information out. Keep in mind though, that this isn't rpm related, it is throttle input related. I can be doing 1000 rpm or 3000 rpm and when I approach 1/3 - 1/2 throttle (I'm sure it is a certain engine load) that it will start to mess up. I'll see if I can get some data from when it is happening.

Thanks, I'll get back shortly

 

[TurboBuRick]

I can go for a drive and find that information out. Keep in mind though, that this isn't rpm related, it is throttle input related. I can be doing 1000 rpm or 3000 rpm and when I approach 1/3 - 1/2 throttle (I'm sure it is a certain engine load) that it will start to mess up. I'll see if I can get some data from when it is happening.

Thanks, I'll get back shortly

Gotcha (Load Related) Not RPM. For the record.

One other thing you can watch is the AF. AF is the signal from the MAF. Watch for it to spike or drop during the condition.

 

[wile2k]

Gotcha (Load Related) Not RPM. For the record.

One other thing you can watch is the AF. AF is the signal from the MAF. Watch for it to spike or drop during the condition.

OK, a little fuel for the fire. At the crossover point to where the problem occurs, the BL goes from 110 to 144 right at that point. So it goes from thinking the car is a bit rich at idle and light cruise, to thinking it is way lean at about an L8 value of 95, tps under 2.0. I have to have a hole somewhere...

 

[Scott89TTA]

My car was acting similar...turned out to be plugs & plug wires. It popped and sputtered with an occasional backfire under hard exceleration & was fine down low. Plugs were old...color was fine but the gap was way high and the electrode was shot. My wires were arcing all over the place too. New plugs and a s set of MSD 8.5 Super Conductors and it is runing great now.

-Scott

 

[TurboBuRick]

OK, a little fuel for the fire. At the crossover point to where the problem occurs, the BL goes from 110 to 144 right at that point. So it goes from thinking the car is a bit rich at idle and light cruise, to thinking it is way lean at about an L8 value of 95, tps under 2.0. I have to have a hole somewhere...

If it was as simple as a hole, it would'nt pop and miss. It just would'nt build as much boost.

 

[TurboBuRick]

When it comes on does it feel like it's missing? Is the poping consistant with rpm when throttle is at half or more?

 

[wile2k]

If it was as simple as a hole, it would'nt pop and miss. It just would'nt build as much boost.

True....

What if I was missing on a cylinder or more than one at that load, all the air / fuel would dump to the exhaust, o2 sensor is going to see way too much o2 and think lean, then add a ton more fuel to try to compensate? So I would already be missing and then dead rich on the cyl's that are firing?

Running full rich and missing on a cyl or more would cause a sputter and pop (unburnt fuel igniting in the exaust) and poor boost production wouldnt it?

Anyone know a good way to test per cylinder?

 

[wile2k]

going to go pull spark plugs and take a look...

 

[TurboBuRick]

And you did verify FP under load? Yes?

 

[TurboBuRick]

going to go pull spark plugs and take a look...

Good call. See if #3 looks different than the rest.

 

[Lee_Burough]

My car was acting similar...turned out to be plugs & plug wires. It popped and sputtered with an occasional backfire under hard exceleration & was fine down low. Plugs were old...color was fine but the gap was way high and the electrode was shot. My wires were arcing all over the place too. New plugs and a s set of MSD 8.5 Super Conductors and it is runing great now.

-Scott

A bad (old) set of wires gave these symptoms to me too.

You may have some esoteric problem causing your symptoms, but I'd bet on something simple.

Check the plugs, wires, coil and ignition module to start with. Its best to swap a known good coil/ignition module, rather than a simple ohm test. Take Razor's suggestion and inspect all your air handling hoses too. Also confirm 43-45 PSI (line off) at the FPR....PLUS one PSI for every pound of boost, you need good fuel pressure.

Does it run well until its heat soaked, or act the same from a cold start? If its something that gets worse as you drive, I'd bet on something electrical.

Don't worry about a flat cam or weak valve springs until you KNOW the electrical system is perfect.

 

[wile2k]

And you did verify FP under load? Yes?

Has a hood mounted direct fuel pressure gauge, it is 38 at idle and increases under throttle...

 

[wile2k]

A bad (old) set of wires gave these symptoms to me too.

You may have some esoteric problem causing your symptoms, but I'd bet on something simple.

Check the plugs, wires, coil and ignition module to start with. Its best to swap a known good coil/ignition module, rather than a simple ohm test. Take Razor's suggestion and inspect all your air handling hoses too. Also confirm 43-45 PSI (line off) at the FPR....PLUS one PSI for every pound of boost, you need good fuel pressure.

Does it run well until its heat soaked, or act the same from a cold start? If its something that gets worse as you drive, I'd bet on something electrical.

Don't worry about a flat cam or weak valve springs until you KNOW the electrical system is perfect.

Thanks for the advice, I have now checked the plugs (broke one so I replaced them all to be safe), wires are new magnacores, coil and ignition I dont have spares of to test...

I have checked the IC hoses and they look good, cant get to the IC until I get home (at my Grandparents now). Fuel seems ok.

It runs just fine at part throttle, whether cold start or hot, the problem seems independent of temperature.

Yeah, I'll keep checking the small stuff until only the hard stuff is left, wouldn't do to change the cam or head gasket and get it all back together to only have the same problem lol.

Bottom line for tonight is that under light load and idle the BLMs are 110, when I get over about 1/3-1/2 throttle or about 95 on the L8 load indicator on the scanmaster the BLMs go through the roof into the 144 range. It seems like as I get to that breakpoint there is a miss which is causing it to read lean and run poorly.

Any other ideas given those symptoms?

 

[sixnboost]

One more thing to check would be loose grounds. One I had a problem with is the coil pack. Make sure it is bolted down tight if its loose it will cause strange behavior also.