intermittant power loss????????????

av winans · 09-04-2000, 11:16 AM

I finally went to my first auto cross after owning the 914 for over five years. It was one hell of a time and a 24hr event at that.
But I had some problems traveling to the race and returning home. During the event the car ran wonderfully never a glitch. At a constant speed and right before deacceleration all power drops, rpms go to 0, but not every time. It acts the same way as when the pressure sensor went, but applying throttle to the engine it revs back up. Less than six months ago the car had a full tune up. In addition to that the pressure sensor was replaced with a new unit not a rebuilt one. The distributor was replaced prior to the turn up but that was a rebuilt one. We have had a good amount of rain around Charlotte NC and the auto cross was held in the rain as well for some of the time. So this may be a contributing factor, but that does not explain why the car ran great during the event, unless it was filled with as much adrenaline as myself. What would cause a intermittant loss of power on the highway or during city driving but never at throttle load? After the power loss it back fires ten times louder that usual, which made driving in town rather interesting. The car is a 73 2.0L with stock D-jet, and the only deviance from stock is the Allison/Crane ignition. Any help or comments would be greatly appricated. I'm too stoked not to drive at the next auto cross.

Aaron Vaughn Winans

JP Noonan · 09-04-2000, 07:02 PM

WAG

1. on/off type problems in my experience are the ignition system. Try puting points back on. Also look for a loose wire going to the coil or brain, and swap the ECU and fuel pump relays out with the headlight relays.

2. If it only does it with a hot engine, see if the CHT sensor is good, and if there is an in-line resistor between the harness and the CHT remove it. A quick/dirty check is to un-plug the CHT and ground the wire going to the brain.

3. Change the fuel filter, maybe the auto-cross stirred up some crud in the tank, O.K. this last one is stretching it a little, so I think I'll stop here

racejoe · 09-05-2000, 06:33 AM

Since it backfires when it kicks back it, it smells like you are getting fuel, so look spark. I had a similar problem with a VW that ended up being the ignition coil getting shorted out by a cracked tach wire near the accelerator pedal, certain throttle positions would cut off the ignition, and a slight movement of the foot would light up the night sky with the back fire. You said "the rpm's go to 0" Is this on the tach? How quick? If it is the tach jumping to zero quickly, but engine is still spinning, I would say for sure your ignition coil is getting shorted out.

racejoe · 09-05-2000, 06:43 AM

It may be possible to get a similar effect by not firing the ignition coil, which could be tied to electronic ignition or dizzy. I would say for sure it is in the ignition system somewhere.

av winans · 09-05-2000, 08:54 AM

After looking at the tach wire to the coil I can see that it is rather cracked and most likely not making good contact. When the rpm's drop out the engine also goes (engine then rpm?). The power loss never happened during the autocross only on the way there and on the way home. Could the deacceleration valve cause this loss if it were sticking? Because this power loss happened on the way to the event I thought maybe it was a dirty fuel filter which I replaced before I started running. Because this was a 24hr event around 4 a.m. I was able to take run afer run and the car reached the same temps as it did driving on the highway. Only difference was the style of driving. Highway a more constant rpm whereas the auto x was much more aggressive and full range of rpms.

Thanks
Aaron Vaughn Winans

av winans · 09-05-2000, 07:31 PM

Well I replaced the iffy connections to the coil. Also I checked the resistance of the CHT. It read 2.3 and change. SO I went out for a drive of about 50 miles. The car got up to temp and then it started the backfire, power loss, and rpm drop thing. I have not changed out the Allison/Crane ignition for the points. Time is where it should be. Please any help is much needed and appreciated.

Aaron Vaughn Winans

racejoe · 09-06-2000, 04:05 AM

Does it backfire-drop-recover or drop-backfire-recover? If it is the first, it may not be ignition, we could be looking fuel. I was half wondering about water in the gas tank yesterday, during the autocross it kept it mixed up with gas pretty decent, but at steady state it could suck a bunch in. I would run some gas into a glass jar and let it settle, see if you have droplets in there. Has this all been on the same tank of gas?

av winans · 09-06-2000, 08:23 AM

Yes, it has all been on the same tank of gas. Just before I headed for the auto x I topped off my gas. It was the good stuff, 93 octane, but maybe it was 93 water. It has been raining quite a bit. The backfire/drop happen so close together I'm really not positive which occurs first, I feel like maybe backfire/drop. I have noticed that backfiring/drop? happed more often the last time out then the first time. It could coinside with running down the gas. Looks like lunch will consist of getting the 914 to give me a sample in a little cup.

Aaron Vaughn Winans

av winans · 09-06-2000, 01:34 PM

I got the 914 to go in the little cup and let it sit for 4 hours after lunch. Nothing but gas, no water bubbles. I guess I'm going to drain the gas and pull the tank to eliminate any question of dirt in the tank or bad gas. I've been meaning to put a screen across the front vent in the cowl anyway. Any other suggestions would be wonderful.

Aaron Vaughn Winans