Major backfires...which one is it?

[jay_rod24]

This question may get bumped outta here as a repeat but I swear I have searched and read till I am carsick. Found a lot of good information but still have a Q.

At high RPM (4500-5000) I get a major backfire and the car falls on it's face. I just rebuilt the motor and did all the upgrades at the same time so I am not sure which is causing this, the walbro pump and 550 injectors or venting to the atmosphere. I do not have any prob's whatsoever at low rpm or idle.

Mods are:
E-VIII ported big 16g
The fuel system listed above
TurboXS BOV

Thanks for any help and please don't me mad at me if it's a repeat!

 

[andymoraitis]

Are you running any form of fuel control with your system like an S-AFC or MAFT? I didn't see one listed in your thread or profile and I'm wondering how you're triggering your injectors and keeping them from running rich. Also, what kind of boost are you running? I don't need to add that venting without a blow through setup is not a good thing.

The major backfire you're describing could be fuel cut. Does the backfire happen and the car continues on as if there was a momentary shutdown in the fuel system and you have to pick your teeth out of the steering wheel?

Let us know,

Andy

 

[1995gsxtreme]

Well you have probably hit the horrible thing called Fuel Cut. If it seems like your car got kicked in the balls then that is most likely it. You can do a couple of things, one get a S-afc or some equal tuning device. Or you could have your ecu re-written for the bigger injectors etc. Also what size fuel pump do you have?

 

[1995gsxtreme]

Well I think I was writing my reply when someone beat me to it.. But there is your answer anyhow.

 

[4g63tsiawd]

Have you noticed any black smoke coming out of your exhaust this is a sign of running rich, which will make your car fall on its face and backfire.

 

[jay_rod24]

Fuel pump is a 255 LPH Walbro. I haven't installed any type of fuel control which was going to be my next step. I have heard that an SAFC was just a "band-aid" for the problem, that the return line off the FPR couldn't handle the volume due to the line size. I was figuring the fuel control was the problem, I just wanted to be sure before buying anything. I've run stock for about a year until I spun a bearing in Dec. due to a crapped out oil pump. (Thank you oil light for the 10 sec warning! )

Anyway, I just got the car back on the road a few days ago, drove it, got the backfires a couple times, then realized i had a junk turbo so now I am sending it back for warranty work. None of that has anything to do with this story though except to tell you that I didn't really see any smoke but I'm sure there had to be some. I can tell I am running rich.

Thanks for the help though and your quick replies. I guess I will try the SAFC when I get my turbo back.

 

[jay_rod24]

Are you running any form of fuel control with your system like an S-AFC or MAFT? I didn't see one listed in your thread or profile and I'm wondering how you're triggering your injectors and keeping them from running rich. Also, what kind of boost are you running? I don't need to add that venting without a blow through setup is not a good thing.

The major backfire you're describing could be fuel cut. Does the backfire happen and the car continues on as if there was a momentary shutdown in the fuel system and you have to pick your teeth out of the steering wheel?

Let us know,

Andy

Forgot to answer this part. As for the momentary thing, I let out of it as soon as the backfire occured as I wasn't expecting it and it sounded like someone got shot. So I didn't pick up my teeth and continue on, I just stayed under the 4500 rpm after that! Also, I know the deal about venting to the atmosphere but the BOV was a gift from my brother so I thought I'd give it a try but I will probably be changing back to recir. eventually. Would that cause backfires under load too?

 

[andymoraitis]

Based on your setup, we both agree that you're running amazingly rich. An EVO III can be supported very well by a 190 and 550's or a 190 and 650's if you really wanted to yank on the boost. It almost sounds to me like your issue is a rich backfire which isn't uncommon when you're flooding the motor and there's tons of unburned fuel present.

There's a number of ways you can tune around this:

1. SAFC and FPR only: As you mentioned, the AFC is a type of bandaid. You'll see huge timing advance since the ECU will see less air and add more timing as a result. This is kind of a "chase your tail" situation and not the solution I'd recommend.

2. SAFC, AFPR, EPROM ECU, Keydiver Stage III Chip: In this case, you have the chip fire the injectors as if they were stock. Since the fuel map on the chip is 9:5.1 (very rich) you can use the AFC to correct and lean it out some more. Since the AFC will only be used for fine tuning, there's less "lying" to the ECU and the timing advance is reduced greatly. This is a much better and safer option than number one.

3. AFPR, EPROM ECU, Keydiver Stage III Chip, Pocketlogger: In this scenario, you still dial in the injectors with the chip, but you also have the chip change the A/F maps from 9.51 to 11:1 (where mine are). Log the car at a certain boost level and use the FPR to either add or remove fuel as needed to lean or richen.

4. AFPR, EPROM ECU, DSM Link: This will give you control over the injectors, timing fuel maps, and a number of other variables, however you'll still need a socketed EPROM ECU since DSMLink requires one. This is likely the closest thing to a standalone that you'll find and the logging capabilities are excellent. If you can afford it, this is really the way to go and is the most flexible of all the "lower cost" tuning solutions.

I'd comment on MAFT setups, but I don't use one and would be speaking out of turn, but many people do with excellent results. If this were my setup, I'd consider what the goals were and also where the next stumbling block will come. Try to remove variables that aren't necessary. For example, having an AFPR is a good thing if you really need a 255 pump, but on your setup, you would have been fine with a 190 and the AFPR (yet another thing to tune) isn't needed. Keep your setup simple and safe and make decisions based on what your aims are.

And yes, I'd replace the BOV with a 1G unit. They hold solid boost to around 21psi and are a relative bargain. Venting may not be the cause of your issues, but it certainly isn't helping.

Hope that helps,

Andy

 

[jay_rod24]

Man, you are full of some useful information. As far as goals - I am not trying to build anything outrageous as this is my daily driver also. Just wanted something a little better performance-wise. Needed a new turbo anyway so I thought why not get a bigger one?

The reason for the pump and injectors is I was told by the person who sold me the turbo that I needed only these items to run this turbo. Boy was he wrong. But I guess it was my ignorance too for not checking into more resources.

What size is the stock fuel pump? is that the 190 your talking about? Can this turbo run on stock fuel?

I definitely can't afford all that computerized stuff. I can something but I don't know which I need to fix the backfire and stumble. So what do you suggest?

 

[hellotbone]

Had a similar problem

Check your
1) coils
2)transistor
3)plugs
4) wired.

 

[CanadianTSi]

A little off topic but have any Pics of how you made the Evo 8 Turbo work??

 

[andymoraitis]

A little off topic but have any Pics of how you made the Evo 8 Turbo work??

I think he means EVO III and not EVO VIII

 

[andymoraitis]

Man, you are full of some useful information. As far as goals - I am not trying to build anything outrageous as this is my daily driver also. Just wanted something a little better performance-wise. Needed a new turbo anyway so I thought why not get a bigger one?

The reason for the pump and injectors is I was told by the person who sold me the turbo that I needed only these items to run this turbo. Boy was he wrong. But I guess it was my ignorance too for not checking into more resources.

What size is the stock fuel pump? is that the 190 your talking about? Can this turbo run on stock fuel?

I definitely can't afford all that computerized stuff. I can something but I don't know which I need to fix the backfire and stumble. So what do you suggest?

Jay,

I strongly recommend that you replace the 255 with a 190, which is the smaller of the Walbro units. A 255 isn't necessary on the EVO III. Your injectors are perfectly matched to your setup, but now you need something to trigger them.

I like simple and easy tuning solutions, especially if you're looking for reliable and very streetable horsepower. What you'll find is that to run a turbo of this airflow properly, that you'll need to deal with other restrictions that will arise once the fuel situation's taken care of. In any event, here's what I think will work for you.

1. EPROM ECU with Keydiver Stage III chip: These are available from Jeff Oberholtzer at DSMChips. With one of these, you can have him lean the air/fuel ratio out (mine is 11:1 instead of the factory 9.5:1), eliminate fuel cut, set the rev limit, set the global and deadtime for your injectors so they work like stock 450's, use the CEL as a shift light and also use the stock boost gauge to measure knock. Cost of the chip and the ECU, which is a plug and play affair is $360.00. For more info, contact Jeff at [email protected] or check their website at http://www.dsmchips.com.

2. Downgrade the 255 pump to a Walbro 190: This will eliminate the need for an AFPR and take a piece out of the tuning equation. Since the chip will control the injectors as if they were stock, using the 190 will not overrun the stock fuel pressure regulator. Cost of this piece is $95.00 from a number of different vendors.

3. Get rid of the stock sidemount intercooler. This is MY biggest restriction right now. I have enough fuel to run 20-21 psi on my Big 16G, but the stock unit will heatsoak after 2 pulls and start to trigger knock (only 5 counts which doesn't retard timing, but I'd rather run no more than 1-3 counts). The cooling efficiency is greater and you'll be able to run a cooler air charge and avoid the knock issue under fairly strong boost levels based on 11:1 A/F ratio in the chip. These are available from DejonTool for $450.00 (http://www.dejontool.com).

4. Replace the vented BOV with a 1G unit. These are widely available from any of the vendors that support DSM Tuners.

Based on your goals, you have MORE than enough flow from the Evo III to have a great time and be streetable. The one thing I don't want you to do is skimp on certain areas since TUNING on these cars makes the biggest difference. Doing one part of this equation likely will not net you the results that you want.

Now, if you can't swing any of that, just buy an AFC, correct for the injectors that way and be careful of how much boost you run since the timing will advance in greater increments the more the ECU is fooled into believing there's less air coming in. This is your least expensive solution and will work, but I don't think it's the best all on it's own. Even with that, you'll won't be able to really make your turbo come alive unless you change out the intercooler.

See? One thing always leads to the next restriction down the line. Good luck and drop me a PM if you have more specific questions that I haven't hit on here.

Andy

 

[jay_rod24]

Had a similar problem

Check your
1) coils
2)transistor
3)plugs
4) wired.

Not sure where ur coming from there WTF We were discussing fuel cut. Anyways, just FYI they are all brand new (those things u listed). Thanks anyway.