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Finished with a rebuild of a series 5 turbo engine back in May, swapped it into my 89 GTUs chassis and had it running by mid to late June. The car runs well, put a little over 2000 miles on it so far and no major problems have come up.
However, I am having problems making boost. The highest I have seen so far is about 3.5 PSI while in third gear, WOT, above 4500 rpm.
Some info on the build:
Stock s5 turbo with ported wastegate
No cat, 2.5" exhaust with jegs high flow mufflers
front mount intercooler
walbro 255 fuel pump
Mazdatrix street port template on intake ports, freehand exhaust ports
emissions delete
I took all my intercooler piping off the other day and went over all the welds with my TIG, making sure there were no pin holes or anything. Wondering what the next step should be in figuring out the low boost problem. I have also tried unplugging my waste gate actuator (Solenoid on the oil filler neck), with little to no noticeable change.
Not sure if it is related, but I am also having problems with the car running extremely rich at cruise (10:1 AFR) and very lean at idle (16:1 and above), however I don't have any problems with misfires, and when the car is in boost, it has good afrs in the 12-12.6:1 range, which I am happy with for now. I notice that the car runs rich while cruising on the highway at light loads, but when you let off the pedal, then get back into the throttle a bit (light acceleration) the AFR "resets" itself and will run at 13.8-14.0 :1 for about 1 minute, then without changing throttle position at all, will dip back down to 10:1 and stay there until throttle position changes again. I have replaced the stock narrow band.
Make yourself one of these (Image from user FuhrerTuner, mine looks different). This goes over your turbo compressor inlet and lets you charge the system with compressed air to find leaks. Around 15psi, you should be able to hear any leaks. This homemade tool is one of the fastest, most reliable leak finders.
1. Check all your clamping points. Willing to bet you will find leaks around your clamps. Everybody does.
2. Check the seals around your fuel injectors. You can get vacuum and boost leaks here too. I have my seals RTV'd in so air can't leak around them.
3. If you are using the stock turbo, or BNR upgrade, and are using the stock solenoid, note that the solenoid is an air bleed out, and not a pressure line in. This solenoid stays shut to have the wastegate operate at normal pressure. It opens to bleed off boost in the wastegate line to keep the wastegate shut longer. Unplugging it means wastegate operates as normal.
4. Make sure wastegate is in the closed position with the engine off (Check wastegate linkage and conservatively remove any slop).
Made the leak tester and used it today. Found that I had some leaks from an intercooler pipe weld, fixed that. Tested again and found a large leak at the compressor outlet coupler and tightened the hose clamp, seemed to get rid of it. Have a few more leaks around the intercooler piping to take care of. Also found my hose that connects the two metal tubes that reference compressor outlet pressure to the waste gate actuator had a leak.
I did find something strange though. When I had the pressure in the piping around 15-20 psi, after a few seconds I could hear a loud “buzzing” or “beep” noise, very similar to the low coolant buzzer (not quite as loud though). I could not find where this was coming from. Tried to get a video but ran out of air and time. Checked the blow off valve (stock recirculating valve vented to atmosphere) and didn’t feel any air leaking out. Any ideas on what his could be?
^sounds like air escaping around a coupler or torn rubber hose. Hard to say without seeing in person. A spray bottle filled with soapy water can help to determine where the leaks are coming from.
Still unable to find where the buzzing noise was coming from, but found also that my homemade blockoff plates were leaking too. Not surprising considering they are just made from some random sheets of 1/8" plate I had laying around. I am going to order a blockoff plate kit to get rid of those leaks. Found that my BOV to charge pipe adapter leaked too, so I built up some weld around the mating surface and that got rid of that leak.
Something strange I noticed was that while testing, opening and closing the throttle plates seemed to have no effect on the pressure held in the system. Seems like opening the throttle would produce some pressure drop (at least momentary) ?
10-01-18, 11:11 PM
