Engine bogs, backfires, and sputters out on the road. Stumped.
03-21-08, 01:03 PM
#1
Engine bogs, backfires, and sputters out on the road. Stumped.
I got a NA S5 I've been working on all week and I am now out of ideas. Here is how the problem plays out.
1) I go out to start the car. The engine fires up and warms up flawlessly and warms up goes to a smooth idle.
2) While parked I can rev the engine up to redline and bring it back dow to idle flawlessly. No trouble what so ever.
3) I get out of the drive way and head out. This is where things go bad. I can drive the car perfectly fine and get up speed if I grandma drive it (very little pressure on the peddle). When I give some gas like any other normal person, the engine starts to sputter and backfire and stops accelerating. This will happen in any gear and any rpm range. Doesnt matter if its at 2k rpm or 6k rpm. When ever I hit the gas hard.
4) Next thing I notice. If I push in the cluch and try to rev it right after it sputters it will continue to do it. If I drive down the road grandma style and rev the engine with the cluch in it will rev to redline just fine.
5) Over the course of the week, tuning and doing test runs ect. I notice the engine is using **** loads of gas. About half a tank going maybe a grand total of 10 miles, probably less. When I pulled the plugs, which are new from a month ago, they were black. I cleaned them up and the problem is still there.
Ok now this is every thing I have done up to this point. Clearly I felt this is a fuel problem. I tested the whole fuel pump circut and everthing seams to be fine. Everything from the egi relay to the fuel pump resistor relay and open circut relay. I then checked the tps. It appears to be in spec ohm wise and adjusted to spec. After that I ripped apart the intake and check both primary and secondary injecters. All in spec. While I was at it I regrounded everything in the engine bay as per Aaron's regound webpage. The problem is still there. I checked the timing, good. Checked the presure sensers, good. Not finding any vac leaks. Did compression tests, all rotor seals are good. It was showing all upper 80s and low 90s, but its still fine.
Mods on the car: Stock airbox replaced with cone filter. Emissions equipment removed; this includes air pump and silinoid rack, FPR is hooked directly to its source vac, the cat and acv is still in place, the cat natrualy is now cracked and very much dead, the acv being as much sitting there dead. Finaly the radiator was replaced with a Koyo. I concidered the cat and acv playing a role in all this but I'm inclined to believe they are not. Just for the fact that the engine as been running strong with them in place for several years now. That being said the 5th, 6th and vdi are dead closed. I lossed them up while I had the intake apart. I plan on putting in the duel RB header/presilencer setup in soon and hooking em up to the pickup tube.
Back the problem at hand. I am now looking at starting to replace pricy items now. By my own judgement I am thinking of replacing the fuel pump or FPR as those are the runner-ups the fuel problem, if that is infact what it is. I figured I'd ask the boards before I start sinking money though. As for the FPR, from reading the boards this doesnt seem like a part that goes bad often. The fuel pump however, just does feel right. I just dont know where to go form here.
So what do you guys think? /long post done
1) I go out to start the car. The engine fires up and warms up flawlessly and warms up goes to a smooth idle.
2) While parked I can rev the engine up to redline and bring it back dow to idle flawlessly. No trouble what so ever.
3) I get out of the drive way and head out. This is where things go bad. I can drive the car perfectly fine and get up speed if I grandma drive it (very little pressure on the peddle). When I give some gas like any other normal person, the engine starts to sputter and backfire and stops accelerating. This will happen in any gear and any rpm range. Doesnt matter if its at 2k rpm or 6k rpm. When ever I hit the gas hard.
4) Next thing I notice. If I push in the cluch and try to rev it right after it sputters it will continue to do it. If I drive down the road grandma style and rev the engine with the cluch in it will rev to redline just fine.
5) Over the course of the week, tuning and doing test runs ect. I notice the engine is using **** loads of gas. About half a tank going maybe a grand total of 10 miles, probably less. When I pulled the plugs, which are new from a month ago, they were black. I cleaned them up and the problem is still there.
Ok now this is every thing I have done up to this point. Clearly I felt this is a fuel problem. I tested the whole fuel pump circut and everthing seams to be fine. Everything from the egi relay to the fuel pump resistor relay and open circut relay. I then checked the tps. It appears to be in spec ohm wise and adjusted to spec. After that I ripped apart the intake and check both primary and secondary injecters. All in spec. While I was at it I regrounded everything in the engine bay as per Aaron's regound webpage. The problem is still there. I checked the timing, good. Checked the presure sensers, good. Not finding any vac leaks. Did compression tests, all rotor seals are good. It was showing all upper 80s and low 90s, but its still fine.
Mods on the car: Stock airbox replaced with cone filter. Emissions equipment removed; this includes air pump and silinoid rack, FPR is hooked directly to its source vac, the cat and acv is still in place, the cat natrualy is now cracked and very much dead, the acv being as much sitting there dead. Finaly the radiator was replaced with a Koyo. I concidered the cat and acv playing a role in all this but I'm inclined to believe they are not. Just for the fact that the engine as been running strong with them in place for several years now. That being said the 5th, 6th and vdi are dead closed. I lossed them up while I had the intake apart. I plan on putting in the duel RB header/presilencer setup in soon and hooking em up to the pickup tube.
Back the problem at hand. I am now looking at starting to replace pricy items now. By my own judgement I am thinking of replacing the fuel pump or FPR as those are the runner-ups the fuel problem, if that is infact what it is. I figured I'd ask the boards before I start sinking money though. As for the FPR, from reading the boards this doesnt seem like a part that goes bad often. The fuel pump however, just does feel right. I just dont know where to go form here.
So what do you guys think? /long post done
03-21-08, 01:23 PM
#2
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Before you get into a pricey repair, Jack your car up and disconnnect your exhaust from the manifold. run it open Manifold and see if the problem goes away...
I had a problem almost identical to this when my cats were clogged -
GL
I had a problem almost identical to this when my cats were clogged -
GL
03-21-08, 02:11 PM
#4
I even made sure by checking that the multi-meter was working by checking a known resistence and its working allright.
Thanks a ton Kompressorlogic
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