4.6 runs rough, rich, stumbles terribly shortly after startup.
06-30-2015, 12:26 PM
#1
Thread Starter
Join Date: Jun 2015
Location: Washington
Posts: 14
4.6 runs rough, rich, stumbles terribly shortly after startup.
Hello, I'm new here so I apologize ahead of time if I don't know the etiquette.
My problem is that shortly after startup, my engine starts stumbling horribly, seems to be running really rich, pings under load, and EATS gas like crazy. Since the problem started I've installed new Accel coil packs, new 24# injectors with a BBK MAF calibrated for 24's, checked and rechecked and then replaced all vacuum hoses, new NTK fwd O2's, checked the TPS, IAC and EGR, all seem to be working fine....absolutely no change. I had BBK long tubes and off-road X-pipe on it for almost a year with no problems, but then I decided to do a bunch of other mods and now it runs like crap. The mods I did since it last ran right are as follows:
Trick Flow T/B and plenum
Typhoon intake
Underdrive pulleys
T56 Magnum trans
FRPP driveshaft and diff w/4.10's
Moser 31 spline axles
Also brakes, shocks, springs, etc etc...
I also bought a custom tune file from Latemodel Restoration to match my mods. I know that the Typhoons are notorious for vacuum leaks, so before installing it I took it apart, sealed and torqued the lower plenum per their specs. I've been searching for threads to help me out on this and have gotten a few good ideas, but nothing has worked so far. I am getting seriously pissed off at this thing after putting over $17,000 into it only to have it run like crap.
Any help would be MUCH appreciated.
Thanks, Vince
My problem is that shortly after startup, my engine starts stumbling horribly, seems to be running really rich, pings under load, and EATS gas like crazy. Since the problem started I've installed new Accel coil packs, new 24# injectors with a BBK MAF calibrated for 24's, checked and rechecked and then replaced all vacuum hoses, new NTK fwd O2's, checked the TPS, IAC and EGR, all seem to be working fine....absolutely no change. I had BBK long tubes and off-road X-pipe on it for almost a year with no problems, but then I decided to do a bunch of other mods and now it runs like crap. The mods I did since it last ran right are as follows:
Trick Flow T/B and plenum
Typhoon intake
Underdrive pulleys
T56 Magnum trans
FRPP driveshaft and diff w/4.10's
Moser 31 spline axles
Also brakes, shocks, springs, etc etc...
I also bought a custom tune file from Latemodel Restoration to match my mods. I know that the Typhoons are notorious for vacuum leaks, so before installing it I took it apart, sealed and torqued the lower plenum per their specs. I've been searching for threads to help me out on this and have gotten a few good ideas, but nothing has worked so far. I am getting seriously pissed off at this thing after putting over $17,000 into it only to have it run like crap.
Any help would be MUCH appreciated.
Thanks, Vince
06-30-2015, 06:20 PM
#3
Thread Starter
Join Date: Jun 2015
Location: Washington
Posts: 14
Set it back to stock, runs the same. If anything, I think it's getting worse :-( I sprayed around the intake manifold and it doesn't seem to be leaking. It may sound funny, but it sounds like it's running with the traction control activated, even though the tires aren't slipping. It clears up for a few seconds and I can run it up through the rpm's with full power, then it starts sputtering and popping as if it's shut down half the cylinders and effed up the timing. It'll clear up for maybe 10% of the time, the rest of the time it's running like a sick 4-banger with the distributor off a tooth. I just don't get it. It runs exactly the same with the traction ctrl on or off, or tuned out with my tuner. I do have MIL eliminators, but that's just for the rear O2's so that couldn't be it. No matter what I've done with the tune, exact same problem. The IAC couldn't cause this I don't think, but I suppose I could clean it anyway.
06-30-2015, 07:15 PM
#4
2nd Gear Member
Join Date: Apr 2014
Location: IL
Posts: 335
OK, let's look at the basics. Is the MIL on? Do you have a code reader? Do you have any trouble codes? Is your code reader capable of reading the O2 sensor output?
Do you still have the stock MAF and injectors? Unless you are drastically changing the ability of the engine to get air in and out (FI, high performance cam swap, TFS heads) you really don't need anything other than the stock 21lb injectors. FWIW, the computer should be tuned for the injectors, rather than the MAF being "tuned" for them, as this frequently causes problems because it's trying to trick the computer with false readings.
Do you still have the stock MAF and injectors? Unless you are drastically changing the ability of the engine to get air in and out (FI, high performance cam swap, TFS heads) you really don't need anything other than the stock 21lb injectors. FWIW, the computer should be tuned for the injectors, rather than the MAF being "tuned" for them, as this frequently causes problems because it's trying to trick the computer with false readings.
Last edited by VTX1800N1; 06-30-2015 at 07:18 PM.
06-30-2015, 08:25 PM
#5
Thread Starter
Join Date: Jun 2015
Location: Washington
Posts: 14
The MIL is not on; the tuner I have is an SCT SF3, never used the data log feature on it so I'm not really sure of all of the capabilities; the only code that comes up is the tattle-tale P1000; I do have the stock MAF and injectors, but it was doing this long before I changed them, and the reason I went from the stock 19# ones to 24's was because as soon as I figure this bull**** out I have a nitrous setup waiting to go in. I heard of the PCU needing to be tuned for the injectors, but I was also told numerous times that if I changed anything to allow the engine to flow a substantially larger amount of air through it that I would definitely need a bigger MAF. In any case, none of those mods did a damn thing unfortunately. I just retorqued the intake AGAIN, no change of course, even though they were a tad loose. How would I tune the comp. for the injectors anyway? Wouldn't the tune from SVE take care of that? I keep getting mixed information, so forgive me if I sound confused. I've been troubleshooting aircraft electrical systems for 30 years, so needless to say I feel I should be able to handle this, but obviously not.....
06-30-2015, 09:29 PM
#6
2nd Gear Member
Join Date: Apr 2014
Location: IL
Posts: 335
4.6 runs rough, rich, stumbles terribly shortly after startup.
First, you have to understand what a MAF meter is. Basically, it's a wire placed in the air stream with a thermistor attached to it. Your engine computer tries to keep this wire at a specified temperature by varying the voltage across the wire. As intake air passes by the wire, it cools it. The computer measures this cooling via the thermistor and varies the voltage to the MAF to compensate and keep that heated wire at the same temperature. It's the mass of the air passing by the heated wire that cools it, thus your PCM can measure the mass of the air entering the engine independent of ambient temperatures and pressures. This gives the PCM an accurate measure of how much air the engine is ingesting. Thus, it's called a Mass Air Flow meter.
A MAF that is "tuned" for a specified injector flow rate just has a different resistance applied to the wire (as one method) vs the factory specification. The problem is that due to the resistance curves of the wire and thermistor vs the mass of the air, it's often not an accurate measurement for what the computer expects to see for a given mass of air.
A much better method is to calibrate the computer (PCM) directly by writing a tune for it (with the tuner you have now- you can contact the manufacturer or better yet, get a dyno tune) that allows the computer to adjust for the larger injectors while keeping the MAF meter readings stock and accurate. Also understand that the diameter of the air intake tube where the MAF sensor is located is also calibrated to the sensor (wire and thermistor). Take the same sensor and place it in a larger tube, and the dynamics of how that sensor measures the air passing by it change.
Your computer uses the information from the MAF meter to calculate the proper injector pulse width based on calibrated injector size, engine speed, load, throttle position, temperature, etc.
Your best bet at this point is to figure out how to read the O2 sensors via your tuner or get a diagnostic reader that is capable of that. You also want to be able to log misfires.
A MAF that is "tuned" for a specified injector flow rate just has a different resistance applied to the wire (as one method) vs the factory specification. The problem is that due to the resistance curves of the wire and thermistor vs the mass of the air, it's often not an accurate measurement for what the computer expects to see for a given mass of air.
A much better method is to calibrate the computer (PCM) directly by writing a tune for it (with the tuner you have now- you can contact the manufacturer or better yet, get a dyno tune) that allows the computer to adjust for the larger injectors while keeping the MAF meter readings stock and accurate. Also understand that the diameter of the air intake tube where the MAF sensor is located is also calibrated to the sensor (wire and thermistor). Take the same sensor and place it in a larger tube, and the dynamics of how that sensor measures the air passing by it change.
Your computer uses the information from the MAF meter to calculate the proper injector pulse width based on calibrated injector size, engine speed, load, throttle position, temperature, etc.
Your best bet at this point is to figure out how to read the O2 sensors via your tuner or get a diagnostic reader that is capable of that. You also want to be able to log misfires.
Last edited by VTX1800N1; 07-06-2015 at 03:15 PM.
06-30-2015, 11:01 PM
#8
Thread Starter
Join Date: Jun 2015
Location: Washington
Posts: 14
O.k., granted, I tend to think old-school. I guess I automatically look for a vacuum leak if it's running rich because that's how normal engines work (carbureted). Like I said before, I've gotten so many different ideas from so many different people, I just don't know what to think at this point. The reason I think it's running rich is because it's blowing a fair amount of black smoke, and smells like unburned fuel. I may be mistaken on this, but that's the way it seems. It also is burning an ungodly amount of fuel, with no power - it can barely make it up the street. Even though I'm sure you know what you're talking about with the MAF and all, like I said, it was running the same way with the stock one, with the stock 19# injectors too - so how could that be to blame?
06-30-2015, 11:15 PM
#9
2nd Gear Member
Join Date: Apr 2014
Location: IL
Posts: 335
4.6 runs rough, rich, stumbles terribly shortly after startup.
O.k., granted, I tend to think old-school. I guess I automatically look for a vacuum leak if it's running rich because that's how normal engines work (carbureted). Like I said before, I've gotten so many different ideas from so many different people, I just don't know what to think at this point. The reason I think it's running rich is because it's blowing a fair amount of black smoke, and smells like unburned fuel. I may be mistaken on this, but that's the way it seems. It also is burning an ungodly amount of fuel, with no power - it can barely make it up the street. Even though I'm sure you know what you're talking about with the MAF and all, like I said, it was running the same way with the stock one, with the stock 19# injectors too - so how could that be to blame?
Right now, you need a scanner than can report O2 data, misfires, Long Term Fuel Trim and Short Term Fuel Trim.
It would also be a good idea to go over all the electrical connections- make sure everything is hooked up where it's supposed to be. It's not impossible to hook an injector or coil up to the wrong cylinder on the writing harness.
Last edited by VTX1800N1; 06-30-2015 at 11:17 PM.
06-30-2015, 11:32 PM
#10
Thread Starter
Join Date: Jun 2015
Location: Washington
Posts: 14
O.k. thanks so much for your help, and your time. I guess I need to give up and take it to a shop that has the right scanner and equipment to diagnose it. I checked all the wiring, it's all good - and as I said SOMETIMES - lol - it runs normally, and like a bat outta hell - but then it goes back to ****. It's like it can't make up its mind where to set the timing and air/fuel mixture. I freakin give up. Arrrrrr. I will be sure to update though when I do find out what it is so that maybe someone else may benefit :-)