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is it fishbite, or what?

Detroit Dan

Detroit Dan

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Epping NH
Since installing the new 4 inch exhaust, I now notice that if I hold it WOT, just before the 2-3 shift I get a stumble, if I don't let up it will do it several times before shifting. Then the SES light comes on, stays on for a few start cycles. Didn't notice really if I was in limp mode while the SES light was on.

I still have about 2000# of weight in the back, don't know if that may be related because I don't normally wind it out like that when it's got any weight on, I just wanted to see what the new exhaust sounded like. I can't for the life of me understand how the new exhaust could be related, so it has to be a coincidence.

So, until such time as I can find time to get it scanned somewhere, does anybody have any guesses what it might be? I should be emptying the load off it soon, and I suppose I'll check the filter again, it looked good not that long ago.

Back when I first put the turbomaster on it I used to always trip the SES if I got to highway speed. Code said boost sensor, replaced it and no difference, then I put in a boost fooler which didn't immediately fix it, but eventually it stopped. I did notice today that a quick rap on the throttle gave me more boost than I expected, I saw a little over 13 for a couple seconds, I thought it was set to run at 10-11, but to be honest I rarely look at that gauge. Think maybe the exhaust is somehow allowing more boost which will require I turn the turbomaster down a bit? I can't see how that could be, I had a 3 to 3.5 straight pipe on it before, so it's not like I was restricting anything.

Other than the stumble and subsequent SES light, the truck is starting and running fine.

Thanks for the input.
 
I guess you're right, I just didn't think I had any backpressure to begin with. My old exhaust was straight pipe. The new one is larger 4 inch with a straight thru muffler.

How can I get away from this stupid SES problem? I thought I had fixed it with the inline resistor on the boost sensor, but apparently not. And I really don't think 13 lbs for 3 seconds is a big deal, but if it's going to trip the light I guess I can try turning the TM back even farther.
 
The point you're stumbling is a peak demand of fuel. I'd be really interested what your fuel pressure is at that point.

My truck stumbled in that exact fashion prior to fixing my lift pump.
 
The stumble can be a PMD issuem and or a fall off in fuel pressure.

Also if it only occurs with the tank at less than 1/4 it can be the safety inlet in the tank sock pickup tube leaking air.

The ses light will come on if the ECM senses over boost.
The only good way to take advantage of the TM is to install a reprogramed ECM on later trucks or a chip 94-95 models.

The reprogram will eliminate the ses light from coming on but also places the issue of fuel delivery, EGT and Boost in your hands.

You will have better performance with a new Program as well as be able to fully use the TM.

Just be sure your lift pump is working right and that you have pressure or at least 1-2 PSI under a full load.

Best

MGW
 
When I've run the boost fooler up too high on mine and forced it to de-fuel, it felt smooth, like you feathered the throttle down. It didn't feel like a stumble. When my IP was starving at full because the LP wasn't working, it felt like a gasser when the ignition was cutting out.
 
I would verify you put the resistor in the right place for the boost fooler, and have you used a scanner to see that your boost guage is accurate to what the PCM is seeing? Mine shows about 1.5psi less than the MAP sensor on the intake sees.

Restriction with a straight pipe at 2.75" stock is significant still over the 4" with a straight pipe muffler. restriction is cause by pressure, which is significantly reduced with increased volume and reduced temperature.
 
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I went from a 3.5 inch straight pipe to 4 inch, wasn't going from stock 2.75. The boost fooler has been in there for years. I replaced the lift pump once already, don't know how long it's been but it should still be good. This has happened with various levels of fuel in the tank.
I think the TM made a huge improvement, even with stock ECM. Obviously a reprogram would be better, I've been wanting one for years I just can't afford one. Every time I save up almost enough something else happens that needs attention.
I haven't done the FTB mod, I'd like to though. I do have one questionable wire on my homemade FSD harness, I need to address that one of these days, it doesn't look real healthy.
I think the SES must be from overboost, cause like I said the boost hit 13 or so briefly, never seen it do that. Just having trouble believing the exhaust could make that kind of a difference.
Where would a good place for the fuel pressure gauge be?
Does seem kind of likely it could be a fuel delivery problem since it is right at max rpm before shifting, if it were going to starve that would be the time.
 
Detroit Dan said:
I went from a 3.5 inch straight pipe to 4 inch, wasn't going from stock 2.75. The boost fooler has been in there for years. I replaced the lift pump once already, don't know how long it's been but it should still be good. This has happened with various levels of fuel in the tank.
I think the TM made a huge improvement, even with stock ECM. Obviously a reprogram would be better, I've been wanting one for years I just can't afford one. Every time I save up almost enough something else happens that needs attention.
I haven't done the FTB mod, I'd like to though. I do have one questionable wire on my homemade FSD harness, I need to address that one of these days, it doesn't look real healthy.
I think the SES must be from overboost, cause like I said the boost hit 13 or so briefly, never seen it do that. Just having trouble believing the exhaust could make that kind of a difference.
Where would a good place for the fuel pressure gauge be?
Does seem kind of likely it could be a fuel delivery problem since it is right at max rpm before shifting, if it were going to starve that would be the time.
Click to expand...


A good place for a fuel pressure gauge is taped to your windshield during the testing phase. 7psi @ idle and it shouldn't drop below 1 psi at any point. Now, with all that being said, this would be ideal. If you can test fuel psi, I think that's the first step. Get a gauge that reads about 0-15 psi. Anything much more than that and if won't be easy to read the low pressures when under load. Remove your drain tube from the bleeder valve near the T-stat. Put your hose on there to run to the gauge and leave the valve open while you're running your test.
 
2 caveats to that advice:

a] make sure you use a hose clamp on the host attached to the fuel drain... it would suck if the hose popped off and filled your engine compartment with fuel.

b] wash your hands before you handle the tape that you are using to put the gauge on the wiper, or else the tape will let go and the gauge will flap around in the wind and beat the hell outta things while you drive all over the road trying to reach out the window and retrieve it.

--Don't ask how I know that.
 
See, now it's fun stuff like this that makes me wish I lived closer to you. I'd love to watch you handle a chain saw or a nail gun with the safeties removed.
 
Dan Hunter said:
See, now it's fun stuff like this that makes me wish I lived closer to you. I'd love to watch you handle a chain saw or a nail gun with the safeties removed.
Click to expand...

Nah....the closer you are to him, the more likely you are to get injured....:nono:
 
Now if you haven't noticed the Bear now wears gold lettering in his avatar name , and if you go poking him too hard, you disappear from the site :D,

BTW Jim good decision IMO by site Admin making you a lead mod, just think when I asked at place if you wanted to wear green, you said you weren't sure if you were up to the task, well buddy you've done good like I always knew you would, congrats on the gold :thumbsup:
 
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