Intermittent Power Loss

At first, driving the RX-8 was a blast, it seemed to pull strong and wanted to go no matter what gear you were in.  After a short while I noticed that on the highway coming home from work sometimes it would not want to accelerate – as if it was running at half power.  Overtaking was treacherous and it sounded a bit weird when revving hard, kind of reminded me of a 2 stroke about to seize.  I found that if I revved it out to the limiter in 2nd gear, it would often pick up again when it hit the second power band at 7000 rpm and clear the problem temporarily, it would still accelerate strong again when I changed up.  Even free revving the engine to the limiter while in neutral or clutch in seemed to help but then it would revert back after a while (like maybe 10 minutes).
The strange thing was that it never seemed to have a problem in the morning on the way to work, only on the way home.  At first I thought it must be temperature related with lower temperatures in the morning but this has happened on the way home when it has been 5°C outside and it has been 16°C a couple of times on the way into work when it has been fine.

Potential Causes

After brainstorming, discussing with other petrol heads and of course lots of searching the ‘net, I came up with this list of potential causes,

  • Low compression – compression test needs to be done by dealer > $100.  In the morning and for the first 10 minutes of driving home, it pulls nice and strong, no starting problems hot or cold, I wouldn’t have thought it would run great at any time if there was a compression issue like worn apex seals
  • Blocked catalytic converter – removed, borescoped and visually inspected, looks fine
  • Spark plugs – after cleaning them with a wire brush, there was much improvement but it came back within 2 weeks and I can’t understand why it would be fine in the mornings, new spark plugs to be installed, dang expensive, cheapest I could find was $100 for all 4
  • Ignition coils – could measure resistance statically but again why would it be fine in the morning and why would bouncing it off the rev limiter make the coil(s) start working better for a while?
  • Vacuum leak – hooked the smoke machine up to the intake, the only leak I could find was where the clip is missing off the airbox, it’s upstream of MAF sensor and thus not a contributing factor
  • Fuel pump – had a very similar issue on the Fiero but that used to cut out (on the way home, never on the way to work!), removed fuel pump, filter looks fine (pic), new fuel pump to be installed

When removing the fuel pump, I ended up breaking the plastic ring that holds the pump in place and snapping the plastic elbow on top because I didn’t disconnect the fuel line.  I posted on the forum at www.RX8Club.com and found a guy not too far away that was willing to sell me an entire housing with bad pump for the absolute bargain deal price of $30.  Once I had a solution for the damaged housing, I ordered a replacement fuel pump.  A Walbro 255 is apparently a common replacement for the RX-8 but I opted for a Kemso pump off eBay that was listed as giving over 300L/h at the same pressure as the Walbro.  It has very similar physical dimensions as the Walbro 255 so I figured it should be a good fit if the Walbro was commonly used and when it arrived I found that it was almost identical, even the electrical connector fitted perfectly.

When winter hit, the RX-8 was parked until they stop salting the roads, so I was able to install the new fuel pump.  I rushed a little bit putting it back in and ended up fouling the level sender float so the gas gauge did not go above half full.  I had to take the pump out again and ensure that the tube and sender wires were routed properly.  Also, the first start after winter did not go well, it was very difficult to get the car started.  Once it was running, the battery would not hold a charge and this also made for some difficulties in starting (quite concerning at the time) until the battery was replaced, then all was good.

Sadly, the first day that the temperature went up into the teens, I started noticing flat spots in the acceleration again, ugh!!  After some more digging I found a lot of people suggesting that the coil life expectancy was about 20,000 miles!  I took the coils off, inspected and cleaned them and the plug leads with WD40, and then put everything back together.  The car instantly seemed to run smoother with an improved pick-up from idle, but on the first drive home in warmer 23°C weather, the power dropped off again.

Could not understand why it was only losing power on the way home or why revving it high, even in neutral would clear the issue.  Then I read that there are two sets of injectors and the secondary set kick in at about 6000rpm, maybe one of the injectors was acting up?  The injectors are behind the alternator underneath the upper intake manifold that must be removed to get access to inspect them.  Since I was using the car, I sprayed WD40 around the general vicinity of the injectors in the hope of hitting the wiring connections and poured a bottle of STP injector cleaner in the tank.  It has been running well for 5 days now but the temperature is down around 10°C again.
Another slight wrinkle is that it only seemed to lose power on the 410 highway on the way home from work, last night I found that the highway entrance I have been using has been permanently blocked so I will have to find a new route home – maybe that will fix the issue?!

I sprayed silicone lubricant around the injector area a couple more times, don’t know if that has helped, but another week of mild weather and avoiding the 410 highway and there has been no signs of losing power anywhere.
Couple more weeks of trouble free motoring, yesterday it was 17°C on the way home and it ran fine.  I have sensed a slight hesitation a couple of times and on a few occasions it hasn’t seemed to pull properly in 2nd, decided to order new spark plugs and leads.  They arrived yesterday and were installed before dinner, then out for a quick test run and wow, what a difference!!  The engine pulled very smooth and seemed much more responsive, it felt like it had about 20 more horses!  I’ll keep an eye on it over the coming weeks, hopefully it’s all good now.
The other day I decided to mix things up and go home the old way, as soon as I got on the highway, it bogged down again!  I engaged the clutch and free revved it to about 8000rpm and then it seemed alright again all the way home.  Got the smoke machine out and did a vacuum leak check, no sign of any leaks anywhere.  Since the spark plugs and leads seemed to make a difference and Tommy keeps telling me how rotary engines love a good ignition, I have ordered some Napol coils from Amazon.

Coils arrived yesterday and were installed last night.  Once again she’s running nice and smooth with full power everywhere but we’ll see how it is on the way home.
So much for the shotgun approach, the issue still persists.  It does not seem as bad but it definitely still loses power on hot ambient days.  My OBDII dongle will no longer connect to the ECM but once that is sorted out, I will log AFR, rear O2 sensor and see if I can record misfires.

On the way home on a hot day a few weeks ago, I stopped at some lights and the car cut out!  I could not get it started again and had to push it off the side of the road.  After about 10 minutes I remembered the brake pedal stomp that I thought would reset the fuel trims, you have to press the brake pedal rapidly 20 times within 8 seconds of turning the key and you should see the oil pressure needle sweep the gauge.  I did this and it fired up!  I found at afterwards that it actually resets the E-Shaft position?  At home I took out the MAF sensor and it looked filthy, dumped half a can of Sensor Clean on it and re-installed, but forgot to reset the fuel trims.  The next day I removed the Room fuse for an hour to reset the trims and it has been running nice for a few weeks now.  It still seems to bog down a bit in slow traffic, it just doesn’t seem to want to pull properly through 2nd gear but after you have opened it up, it pulls fine.  It isn’t perfect but it is a fun drive and I am steadily building confidence in the reliability.

Long overdue update: still running nice but not perfect.  The idle is still hunting sometimes and the long term fuel trim is high (12%) at idle but about zero at 2500rpm suggesting a vacuum leak.  Many smoke tests have been done, sprayed propane and ether (not at the same time) around the engine bay, applied pressure and sprayed soapy water around intake, removed upper intake – can`t find any sign of a leak anywhere.  Power still seems down sometimes but it only goes down to about 90% now.

After leaving the car for two weeks, it took an age to get started.  The battery was a bit low so I jumped it off the spare battery but even with the starter spinning nice it took quite a few attempts and a fair bit of cranking before it would actually start.  Once it started, it ran rough for a while with smoke coming out the exhaust; this is suggesting to me that there might still be a fuel issue.  As a minimum, I intend to install small clamps on the fuel lines in the fuel pump housing – need to get the 924T back together first.

The Fix

Took the fuel pump out … again … and checked that the fuel lines were all attached and in good condition, everything looked good.  Since there were no signs of issues there and with me having a spare siphon assembly, I decided to try the siphon mod mentioned in the post at rx8club.com.  The idea for this is that there is a spring loaded blow-off valve at the top of the siphon assembly that is designed for the stock pump that works at a lower pressure, with the new aftermarket pump, this valve is getting opened at a lower operating condition reducing the fuel supply.  Rather than melting something in to block the valve, I figured that if I block off the outlet, there will never be a pressure difference over the valve to open it.  The first idea was to use a hose clamp but the screw mechanism fouled other components so a simple piece of hose placed over the top was used.

Once the fuel pump assembly was installed again, it took only a few tries before it fired up – this is unheard of after sitting for a couple of weeks.  After a couple of weeks running and clearing the old gas out of the tank, there has not been one single instance of power loss.  One of the most frequent places it would suffer was at the end of the highway after cruising for a few mins; before it would struggle to maintain speed going up the hill in 5th gear, now it will easily increase speed by 10kph while climbing the hill in 6th!  It also really struggled to accelerate to overtake in 3rd after getting off the highway but now it blasts again so I can overtake with confidence.  We have seen the temperature get into the teens so I’m fairly confident that the issue was indeed fuel related and changing out the fuel pump for an aftermarket version requires the modification to the siphon.