Lost power and stumbles

[datsunan]

So I did some work on my car that should have increased HP but when I dynoed it it went down. Work done, new light weight fw and pp, replaced 3/8 fuel line with new 3/8 fuel line, cleaned fuel filters, new 3" 45deg intake hose to turbo, re-plumbed wastegate diaphram hoses to turbo outlet instead of manifold. Now I have a mis-fire that I can't figure out. I have checked for leaks and fixed two small ones, checked plugs, looked rich, adjusted fp down look good now, compression test 120psi on all, changed plugs, wires, coil, intalled new ground wire to block, disconnected wg signal hoses, checked and double checked ecu plugs and maf plug, checked plugs on injectors, chts and tps operation, fuel pressure is fine, timing makes no diff. I've also searched and tried every suggestion that I have come across, no luck. The car idles ok but as soon as I'm on the gas it sputters under load, as rpm goes up it is less aparent but shows up on the dyno as a 60hp lose. If I am in 3rd step on the gas and break to spool up the turbo it starts sputtering and then backfires into the manifold, it will also do this in 5th on a hill wot. Any other things I can check? Please help, Its making me really cranky.

[Bernardd]

what was the fp at when you changed it? what did you change it to? why was it out of spec? it should be 36 with no vac reference. is your new intake hose collapsing? i believe that has happened before.

 

so it runs ok when not in boost?

[datsunan]

It was at 42psi now its at 37, I had raised it becuase of the detonation I was having. I thought my new intake was collapsing so I put some 3" metal supports in it, no way it can collaps now. It runs Ok on boost but my hp levels are way off on boost so I think the miss is still there just not as noticable as rpm increases. It ran ok on the higher fp until I did my mods then it went to crap.

[BrandonsZ]

backfiring (in the exhaust side) is an indication of unbrunt A/F mixture getting into the hot exhaust a clear indication of miss:

You're not getting spark to all cylindars or intermittant spark.

1. Check plug wires, one may be grounding out. 45%

2. Check ignition module pull plugs see if any look different (if they all look sub par it might be a random misfire caused by ignition module. 45%

3. weak injector or stuck injector (you'll see the spark plug indicate which, no doubt). 10%

 

backfiring into the intake is an indication of improper timing.

1. You have two switched plug wires 90%

2. Timing gear chain/belt dammaged or skipped.

 

Your problem is most likely electrical, don't give up and don't hesitate to recheck something you've already checked, it's a slippery problem especially if it's intermitant.

 

Good luck.

[datsunan]

It is definitly a backfire int o the intake and not the exhaust but changing the timing did not change it. I had removed the dist. but it only goes back in one way so I'm thinking its not timing. I will have to check my dist wring and plug wires. I'll also have to see if I can find anouther ign module, I had not thought of that as being a sorce of the problem. Have you seen that happen,that they work inter. I thought it was like a transistor, it either works or it does'nt, I hope your right. Thanks for the feedback.

[VinhZXT]

A friend of mine had a backfire thru the intake and it turned out to be a crack distributor cap. So my suggest is try a new distributor cap. Good luck

[BrandonsZ]

It is definitly a backfire int o the intake and not the exhaust but changing the timing did not change it. I had removed the dist. but it only goes back in one way so I'm thinking its not timing. I will have to check my dist wring and plug wires. I'll also have to see if I can find anouther ign module, I had not thought of that as being a sorce of the problem. Have you seen that happen,that they work inter. I thought it was like a transistor, it either works or it does'nt, I hope your right. Thanks for the feedback.

 

 

The ign mod on my F150 got hit by rad fluid coming from a leaking radiator. It worked only sparatically and the retarded computer pointed at the mass air flow sensor. It caused missing, and intermittant stalling, but never backfiring. I left the MAF sensor alone and replaced the Ign mod. Fixed.

 

 

Backfire into intake:

 

90% two switched plug wires,

 

- check, recheck, find a second source for info.

I drove my Suburban with two swtiched plug wires for a week before I figured it out. The only simptom was occasional backfire and low power. Granted the engine was two steps in the grave.

 

5% Distributor system, carbon trail, cracked cap, rad fluid in the cap (don't ask) bad pickup for distributor (not ignition module).

 

-with as much as you have put into this car, just get a new distributor.

 

 

2% two plug wires (neatly stowed and parallel for a long distance) are cross talking (inductive->Electromagnetic Leakage->inductive).

 

-If it happens often, then you can try to unplug each wire one at a time and listen for it to happen, if it stops happeneing when you remove one wire in particular, reroute that wire so that it is routed an entirely different way, and recheck. This is really hard on the cat so do it cold.

 

-replace the wires, then pull them apart so that they are inches from eachother in route and only cross at near 90 deg. This is almost never a problem anymore especially with spiral wound shielded cables. (MSD)

 

 

1% hot head due to carbon buildup causing deiseling as fuel is injected and intake valve is open.

 

-remove the head and check. Very unlikely.

 

 

1% if you have a knock sensor, your system had computer controlled timing, the computer may be getting a spurious signal and tries to compensate by adjusting the timing way off for just a split second.

 

-replace knock sensor.

 

1% gremlins, sorry, no known solution. Replace car or take it to your local grease monkey who will most likely plug in the computer, scratch his head and spout extraniuos babbling as his a** becomes itchy beyond political correctness. Then he'll have a soda and sit on his aformentioned a** or work on a personal poject until it's time to go home. No doubt his personal project will involve stealing parts off your car and replacing said parts with junk or garbage. The vampires at the service desk will charge you per hour plus a nominal overnight storage fee. Good luck.