Power loss...


Hello All and thank you in advance for your replys.

Over view: Chump e30, 88 chassis/harness, 90 m20 135k (out of a vert garage queen).

In a shake down yesterday at Chin/VIR we were experiencing no power at 5k+ in 4th & 5th gear. 1st-3rd would pull hard through to redline. All gauged vitals look great. Swapped out several ECU’s, coil and new fuel filter. The fuel set up is 16.5 tank with lift-drv & 318 hi pres-pass. Tank is vented with tube looped up rr c-pillar and capped with paper cone filter. We need to rework the vent setup as its spitting fuel. Also the speedo is not working.

Any ideas/thoughts??? Plz direct us what to check…

Fuel tank venting


Does anyone know the effects of a fuel tank NOT venting correctly… will it starve the pump/s?


The AFM can cause low power in that rpm range as well as the tps.


Afm/tps just in 4th & 5th?


On the vent tube, loop it three complete loops then install the paper filter. It will not leak.


After thinking about power loss, it is one of two things. First, air restriction at speed. Second, lack of fuel…you may have pressure at idle, but not in the upper gears…its a flow problem. Change the main pump to an o44 and ditch the intank pump.


We’re going to adjust fuel system…

The se30 exhaust (poore) currently has no heat sheilds. We’re gonna install sheild or wrap at tank area.
The expansion tank in rr well is deleted and the lg vent tube is attached directly to gooseneck fill tube, the sm vent tube is vented/looped up c-pillar. We’re gonna tee both together and vent/loop up pillar with larger tube and cap off gooseneck.

We do another shake down and bring an extra AFM if that does not resolve.

Thanks for input/replies!


Too much guessing. Consider temporarily putting a fuel pressure on and then go make the symptoms occur. You can do this by plumbing in the gauge and then strapping it to a windshield wiper. We’ve done this at the track several times. As a permanent solution, put a gauge on your dash.

If your FP gauge doesn’t show any FP problem, don’t waste time on fixing fuel supply problems.

At the same time, put a fuel to air ratio meter on your dash. This can provide key troubleshooting info.

Some years ago, '09 maybe, I went thru engine management hell. I did everything I could come up with trying to fix the problem, to include pulling apart every electrical connection that could possible be related to engine management, surfacing the metal, and then re-assembling with conductive grease. The problem turned out to be the AFM. A couple well-intentioned souls had “adjusted my AFM dial”, a technique that to this day is hotly debated, and over time that made my engine run leaner and leaner. The F/A meter on my dash was telling me what the problem was, I was just too stupid to believe it.

My point is that it’s a mistake to randomly attack a system. First, spend lots of time trying to figure out what is causing the symptom, or rule out possible causes. Connecting a fuel pressure gauge to your system and then doing hard laps, for example, is a trivial effort and saves a lot of hassle by ruling out a number of possibilities.

Re fuel tank venting. Last year I noticed that my tank had developed some kind of venting problem. A low pressure zone was being created in the tank as fuel was removed. The solution was a vented gas cap. Cheap and easy.


You may want check the Chump rules on fuel vents. No vent mods allowed except with fuel cells. I had similar issues and it was a plug not firing. I would check the plugs and also the injector connection. The m20 pulls well on 5 cylinders in the lower gears.