Popping on "tip in"

[Mavdaddy]

My truck has been a real source of joy over the years but as with any "lover" there are bad times as well as good times. Last year I discovered that even though I was running the correct distributor gear (per Lunati) it chewed up the gear ring on the cam. I decided to go back with a Competition Cams unit that was very close to the original Lunati. The only difference being a few thousandths more lift and a wider LSA. While doing this I also added an air to air intercooler and replaced the distributor with another factory style dizzy.

Now I have an annoying popping in the exhaust when tipping into the throttle. The engine is stumbling a little while this is happening. It starts at about the point that the manifold vacuum goes to zero and before the boost comes in, and the FMU spikes the fuel pressure. Once the boost and added fuel arrive the motor pulls like it has never pulled before and it sounds like everything is working in sync. No popping on deceleration, good idle, good cruse. The drivability is really bad.

Here is my set up.

408, AFR 205, Comp Cam, Pro-M conversion with Pro-M MAF and 76 lb/hr injectors, A9L, MSD 6-BTM, FMU, Vortech Ti Trim, Air to Air intercooler, 70 mm BBK,

I have explored so many avenues on this thing. Here is a list of things I have tried with the hope of finding or eliminating the issue.

• Cylinder leak down test - all good.
• Cleaned the MAF.
• Tested and adjusted the TPS.
• Replaced the MAP sensor.
• Checked various fuel pressure settings (as high as 60 PSI and low as 32).
• Replaced the ignition module.
• Replaced the coil.
• Checked for vacuum leaks.
• Replaced the pick up in the distributor.
• Plugs and wires.

Sometimes we struggle with things so much that we focus in on the same issues and can't see the whole picture. I keep thinking it is a fueling issue but maybe not. Valve train timing issues? Any enlightened suggestions would be greatly appreciated.

 

[FMOS Racing]

That's lean tip in, it's not getting enough accel fuel. Edit - I thought the MAP wasn't used, but the A9L does use it for BARO.

With the combo you have, I'd sure recommend a wide band O2 sensor and gauge!

 

[Mavdaddy]

That's lean tip in, it's not getting enough accel fuel. BTW, the MAP sensor isn't used at all - IIRC the Pro-M conversion doesn't even use it to reference BARO.

With the combo you have, I'd sure recommend a wide band O2 sensor and gauge!

Thank you for your comments.

I bought that kit from a guy here on the site maybe 10 years ago. It came with a MAP sensor already plugged into the harness coming out of the box that houses the ECU. Now I have two of them under the hood. The original factory one (that I assumed was not being used) and the one that came with the kit. That is strange.

The O2 sensor is something I have intended to add for a long time but haven't. Very irresponsible of me I know. A friend of mine that has tuned the truck on his chassis dyno has told me the same thing. He says I am gonna do some real damage one day if I don't watch my AFR.

So you are suggesting that I may be on the right track with it being a fueling issue. I am curious as to why all of the sudden I am having this problem. I wonder what might have changed that would bring this on? I wasn't having it before the cam and distributor change? Raising the fuel pressure seemed as though it helped but not for long.

 

[FlatOut]

So you have had it dyno tuned and you use an FMU?

have you rechecked your timing just to confirm its correct and made sure your spark plug wires are on the correct firing order? are your rockers adjustable? too tight maybe?

Jeff is almost always correct so lets say the timing and firing order are correct after your cam swap. When was the last time you replaced the fuel filter. Pinch/kink any lines during the reassembly of the intake?

 

[Mavdaddy]

So you have had it dyno tuned and you use an FMU?

have you rechecked your timing just to confirm its correct and made sure your spark plug wires are on the correct firing order? are your rockers adjustable? too tight maybe?

Jeff is almost always correct so lets say the timing and firing order are correct after your cam swap. When was the last time you replaced the fuel filter. Pinch/kink any lines during the reassembly of the intake?

Thanks for your input.

The firing order is correct, fuel filter is good, and no lines are pinched or kinked.

The rockers are Jessel shaft mounted and adjustable. That was actually the first thing I checked. I figured an exhaust valve was opened.

The fact is my friend is very good with the newer systems and with the Holley system. He has adjusted tables and burned a couple of chips for me but they have not worked so well. I added the FMU because we were able to put together a tune that offered good perfomance, and it was a good driver with the fuel pressure down in the 35 psi range, but it needed additional fuel pressure to be fat and safe at full boost.

It all worked well until I made the recent changes.

I don't know anyone I can trust to tune it in my area so I am not sure how to move forward. I considered going to a Holey Terminator system but I have no idea how to do that and keep all of my factory gauges working. And then there is the whole transmission control issue to deal with.

 

[FMOS Racing]

The fueling could've been marginal before, but the different cam characteristics pushed it just enough that it's lean enough to pop.

I'd be a bit uneasy about a mass air tune with adequate injectors and a properly curved meter that needs an FMU.

You could get a Stinger ECU that just bolts in place of the A9L; it's a plug and play bolt in, and then have it tuned. Or you can sell the Pro-M combo and pick up the Stinger ECU with the transmission module (which is what I have in both my turbo truck and my nearly stock truck).

If he can tune the Holley, he can tune the Stinger stuff. Same tables, just a slightly different windows interface.

I ran a Pro-M conversion for almost 25 years with pretty decent results, but the new engine management stuff is so far advanced from that, it's tough to even compare.

 

[Mavdaddy]

The fueling could've been marginal before, but the different cam characteristics pushed it just enough that it's lean enough to pop.

I'd be a bit uneasy about a mass air tune with adequate injectors and a properly curved meter that needs an FMU.

You could get a Stinger ECU that just bolts in place of the A9L; it's a plug and play bolt in, and then have it tuned. Or you can sell the Pro-M combo and pick up the Stinger ECU with the transmission module (which is what I have in both my turbo truck and my nearly stock truck).

If he can tune the Holley, he can tune the Stinger stuff. Same tables, just a slightly different windows interface.

I ran a Pro-M conversion for almost 25 years with pretty decent results, but the new engine management stuff is so far advanced from that, it's tough to even compare.

Thank you again. This is why I reached out on here. I had no knowledge of the Stinger ECU. I looked at their web site and read up a little on it. Looks pretty darn capable. I can tinker with this tuning myself? No chips to burn?

My experience so far with the current setup has been that tuning on the dyno often makes great numbers but the drivability is not good. I drive this thing and love it! It's no a trailer queen. If I can keep my current setup and my factory gauges working that is what I would like to do.

Thanks to some hardened parts and a Punisher valve body tweaked to match my setup, I have my transmission behaving perfectly right now. Not sure I want to mess with it.

 

[FMOS Racing]

If you use the Stinger PxS (the "Shift" version with the transmission controller), you have to relocate 3 wires in the stock harness, install a wideband O2 sensor (I used the factory O2 wiring and built a pigtail to use the wideband instead of the regular O2 sensor), follow the rest of the install instructions, and it should be immediately drivable. Plug in a laptop, use the autotune feature, cruise around a while, working your way up the the throttle, and it will get you really close. Then you can have your professional dyno tune it for the last little bit.

I've done 100% of the tuning on both of my trucks myself - others here do the same. I'm extremely happy with how they run, both engine and transmission. It takes a some time and there is a little bit of a learning curve, but I think it's a lot of fun to tweak my stuff. And I absolutely love being able to see everything that the ECU is doing. I think the Perfect Tuning gauge that Stinger sells is ugly, but I have one in my '94 and the amount of information you can get from one gauge makes it really nice - I watch the O2 correction and MPG constantly. I'm also using the Spartan 2 wideband in my '94.

 

[FlatOut]

The stinger ECU is very commonly used by guys on this site. Lots of support here and thru stinger themselves. big advantage over MAF tuning capability. No chips to burn. Live feeds and instant changes while engine is running. infinitely adjustable. Most guys run the "shift" version and control all the shifting aswell as the engine thru the same unit. I run a manual trans swap so I don't use the "shift" version. and I think a few others run the non shift version but use the quick 4 along side. my biggest complaint with the system is the name, otherwise very capable system and with your combo it seems you would benefit from building a save tune.

 

[Mavdaddy]

The stinger ECU is very commonly used by guys on this site. Lots of support here and thru stinger themselves. big advantage over MAF tuning capability. No chips to burn. Live feeds and instant changes while engine is running. infinitely adjustable. Most guys run the "shift" version and control all the shifting aswell as the engine thru the same unit. I run a manual trans swap so I don't use the "shift" version. and I think a few others run the non shift version but use the quick 4 along side. my biggest complaint with the system is the name, otherwise very capable system and with your combo it seems you would benefit from building a save tune.

So you don't like name "Stinger"...

I thought I read on their web site that you can tune using MAF or SD. You find SD to be a better way to go? Drop the MAF, add a wide band and start with a basic tune?

 

[FlatOut]

the ECU is called PIMPx, Pimp XS or PIMPxSHIFT. stinger is cool

 

[Mavdaddy]

I was on their web site just a few minutes ago and noticed that. I agree with you. Gonna call them on my lunch hour and get the ball rolling on this.

 

[Mavdaddy]

Sent them a message and hope to get a call back. Not sure how much detail they need on my set up. Not sure what additional items would be good to get. I have no idea what communication ports would be best.

Hell I get a new cell phone and I have to get my grandkids to hep me set it up.

 

[FMOS Racing]

My opinion, don't use the USB port. Get the expansion port with the communications stinger. It's so much easier to install and live with.

There's a little complexity to setting up the jumpers, but you only have to do it once. Their instructions are pretty complete.

I also hate the name. Nearly refuse to use it.

Definitely no reason to use a MAF with a modern, MAP-based ECU. MAF provides a greater range of accuracy for smog related stuff from the OEMs, but that's not our priority...

 

[FlatOut]

My opinion, don't use the USB port. Get the expansion port with the communications stinger. It's so much easier to install and live with.

There's a little complexity to setting up the jumpers, but you only have to do it once. Their instructions are pretty complete.

I also hate the name. Nearly refuse to use it.

Definitely no reason to use a MAF with a modern, MAP-based ECU. MAF provides a greater range of accuracy for smog related stuff from the OEMs, but that's not our priority...

What is this expansion port you speak of? I've used the USB for like 10 years now but curious what the other option is. Looked on the site and doesn't give me any hits using a few select key words.

I sure hope PIMP is an acronym for something and not just a random term they came up with.

The interface may be a bit overwhelming when you first open it up but its not to bad once you make your way around it.

 

[Mavdaddy]

I found a couple of videos on how to set it up. Links keep taking me to "mega squirt" instructions. Are they affiliated?

When I was creating a unit to put in my cart there was an option to select the interface and Jeff's suggestion was on there.

I am also a "JEFF". Let me know if we are not on a first name basis here. I wasn't sure how to address you. I will refrain if you prefer.

 

[Raymond_B]

I found a couple of videos on how to set it up. Links keep taking me to "mega squirt" instructions. Are they affiliated?

When I was creating a unit to put in my cart there was an option to select the interface and Jeff's suggestion was on there.

I am also a "JEFF". Let me know if we are not on a first name basis here. I wasn't sure how to address you. I will refrain if you prefer.

The Stinger setup (I also hate the name) is a customized Megasquirt based (actually 2, one for engine one for trans) unit that Stinger built upon. They did a lot of work to make it very much plug and play. So anything you watch about Megasquirt will be similar to what you will have with a Stinger unit. Main caveat about that is there are a multitude of different Megasquirt versions and info sources. While High Performance Academy does not have a huge amount of Megasquirt info, what they have is solid. Here's a good primer https://www.hpacademy.com/blog/how-to-tune-using-megasquirt-online-training-course-tunerstudio/

On your current setup, I agree that without a wideband you really are guessing, but yeah it really does sound like you are leaning out when you tip it in. For grins I would double check the base timing. You could also bump up the fuel pressure, it might run worse, but if it helps the tip in you know it's fuel related. But again you're gambling with all those parts and no wideband.

 

[Mavdaddy]

The Stinger setup (I also hate the name) is a customized Megasquirt based (actually 2, one for engine one for trans) unit that Stinger built upon. They did a lot of work to make it very much plug and play. So anything you watch about Megasquirt will be similar to what you will have with a Stinger unit. Main caveat about that is there are a multitude of different Megasquirt versions and info sources. While High Performance Academy does not have a huge amount of Megasquirt info, what they have is solid. Here's a good primer https://www.hpacademy.com/blog/how-to-tune-using-megasquirt-online-training-course-tunerstudio/

On your current setup, I agree that without a wideband you really are guessing, but yeah it really does sound like you are leaning out when you tip it in. For grins I would double check the base timing. You could also bump up the fuel pressure, it might run worse, but if it helps the tip in you know it's fuel related. But again you're gambling with all those parts and no wideband.

Thanks for jumping in.

I actually did raise the fuel pressure at the regulator and it seemed to help for a while. I think this is the video I was talking about. I think it is like two hours long. I was gonna pop some popcorn and try to watch it tonight.

 

[slow94]

If you use the Stinger PxS (the "Shift" version with the transmission controller), you have to relocate 3 wires in the stock harness, install a wideband O2 sensor (I used the factory O2 wiring and built a pigtail to use the wideband instead of the regular O2 sensor), follow the rest of the install instructions, and it should be immediately drivable. Plug in a laptop, use the autotune feature, cruise around a while, working your way up the the throttle, and it will get you really close. Then you can have your professional dyno tune it for the last little bit.

I've done 100% of the tuning on both of my trucks myself - others here do the same. I'm extremely happy with how they run, both engine and transmission. It takes a some time and there is a little bit of a learning curve, but I think it's a lot of fun to tweak my stuff. And I absolutely love being able to see everything that the ECU is doing. I think the Perfect Tuning gauge that Stinger sells is ugly, but I have one in my '94 and the amount of information you can get from one gauge makes it really nice - I watch the O2 correction and MPG constantly. I'm also using the Spartan 2 wideband in my '94.

How is the install on the perfect tuning gauge. May be something I would purchase.

Sent from my Pixel 6 Pro using Tapatalk

 

[Required]

Keep us updated on the Stinger project. Would be cool if you could zero in on the issue first so it doesn’t become compounded with additional variables. +1 for Fuel pressure and AFR gauges. I don’t know if they “saved” me as much as led me to the right flow chart for some issues. By the time I hear the alarm chime bad things prolly are in motion I can’t stop. Maybe time for me to go Stinger too.