Engine Surging/Bucking/Hot manifold once warm

[Brad Ferguson]

Hi all, new to the forum, been watching erics videos for ages now, decided to join up as I have nearly run out of ideas for our car. I have spent weeks on my regular forums and google searching now and cant seem to find solutions to our problems, so here it is lol.

Car : 1989 Mazda 626 4WS 2.2L Turbo
We have had the car for 9 months now, we bought it off the previous owner who had it sitting in his backyard for 10years. The engine has been rebuilt with all new bearings, pistons(increased from 7.8:1 to 8.6:1 ratio), rings, overbored and honed at 0.020, brand new head with new valves, springs and HLA’s. Every sensor is brand new and all vacuum lines and coolant hoses been replaced. Plus a lot of work on the suspension, braking and body side of things. Also running 8.0mm leads, MSD coil pack, new dizzy rotor and cap, and new plugs. Also a Tomei AFPR. Running standard turbo on 7.5 PSI boost. Injectors removed and ultrasonically cleaned and tested and performing to factory specs. Fuel tank drained and cleaned, new fuel filter, new fuel pump and new transfer fuel pump.
We got the car running and registered but around 1 week later, started getting a bucking when pressing the accelerator, felt like bunnyhopping the clutch from a standstill. over the next few days got worse and worse to the point it would do it every time we started producing boost and pressing the pedal more than 50%. This only happens after the car has warmed up, can drive for 10-15mins from cold and it will pull hard, boost well and run beautifully smooth acceleration and good power on boost. We thought we had weak spark, so installed the MSD coil and the 8.0mm leads and gapped the plugs to .6mm just to check. I took it for a night run when I finished installing the new coil and leads. And after 15mins was bucking again same as before. I popped the hood to see if I could see anything out of the ordinary, and noticed that the turbo hot side and exhaust manifold were glowing red.
This is what I have done so far since the bucking first started.
– Installed an AFPR with gauge to monitor fuel pressure (30-35psi as per WSM)
– Installed a new ignition control module
– Replaced ECU
– Installed the higher output MSD coil, 8.0mm leads and gapped plugs to 0.6mm
– Tested O2 sensor and is within factory specs
– Have checked the Cat Converter – one of the catalysts is bent but not broken and can see light through the honeycomb.
– Have checked ignition timing, have tried it at 6deg, 8deg and 10deg BTDC (factory is 10)
– Have pulled codes, was getting an O2 sensor code and purge solenoid code, replaced the purge solenoid and put a new plug on the O2 sensor to harness, and both codes now gone.
– checked turbo and spins smoothly and has no deflection that I can feel. (doesn’t prove that it is good though)
– Tested wastegate operation and opens and closes smoothly.
– Replaced VAF with two others, all 3 VAFs test correctly to the WSM.
– TPS is within spec.

Sorry for the long list, just want to pass on as much info as I can. We are running out of ideas :(. The one thing I am not happy with, but not sure if it would cause these problems, is the timing belt, we installed it with cyl1 at TDC and installing the belt with the cam as close to the mark as possible, if I turn the crank so that the timing mark is 100% on the mark the crank pulley is showing that we are 2deg BTDC, if I move the cam back or forwards one tooth the mark is then no where near the cam timing marks.

Any ideas of what else I could check would be greatly appreciated, thanks in advance everyone.

turbo and manifold after 25 mins only two hard pulls over 4000rpm in this time

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[Brad Ferguson]

cheers again eric. I have been on forums talking to people who have done the same work as I have done and most of them are still running stock ECU without any issues. I will go aftermarket if I have to just a money issue atm lol.
I have been monitoring my fuel pressure since i last posted, and I am thinking that I may have a dodgy fuel pump, but not sure. I have installed a pressure gauge onto the FPR. I set the pressure to 40psi with engine off, when I start the engine up it drops to 32-33psi, all this is as per WSM. pressure is steady and needle holds quite still, but after driving it until the surging starts if I check the fuel pressure again it has dropped and the needle is bouncing all over the place from 20-30psi. If I wind the pressure back up to correct levels it keeps bouncing. I have to let the car sit for 2-3 hours before i can start it back up without pressure fluctuations. It is a brand new fuel pump, but i have had a few dodgy new parts for this car since the rebuild start. could this be a sign of a dodgy fuel pump? before i spend a lot of money on a new ECU? thanks agin

[Kevin Criswell]

[quote=”EricTheCarGuy” post=76089]You may need to get that aftermarket ECU so you can program it to run your engine. Anytime you modify things you run into issues like this. It’s kind of a ‘process’, or a work in progress if you will.

Good luck and keep us posted.[/quote]

That is why I have been silent on this one. Heavily modified engines are real hard to dial in and without some specialty equipment might never get “right”. I have seen guys have to buy thousand dollar flashers, copy the operating system, modify it at the ROM level and re-flash the PCM to get the vehicle to operate how they want it to. Without actually being there to see the exact setup any advice is just shooting in the dark.

[EricTheCarGuy]

[quote=”thefergusons” post=76479]cheers again eric. I have been on forums talking to people who have done the same work as I have done and most of them are still running stock ECU without any issues. I will go aftermarket if I have to just a money issue atm lol.
I have been monitoring my fuel pressure since i last posted, and I am thinking that I may have a dodgy fuel pump, but not sure. I have installed a pressure gauge onto the FPR. I set the pressure to 40psi with engine off, when I start the engine up it drops to 32-33psi, all this is as per WSM. pressure is steady and needle holds quite still, but after driving it until the surging starts if I check the fuel pressure again it has dropped and the needle is bouncing all over the place from 20-30psi. If I wind the pressure back up to correct levels it keeps bouncing. I have to let the car sit for 2-3 hours before i can start it back up without pressure fluctuations. It is a brand new fuel pump, but i have had a few dodgy new parts for this car since the rebuild start. could this be a sign of a dodgy fuel pump? before i spend a lot of money on a new ECU? thanks agin[/quote]

If the fuel pressure is all over the place like that then you may be onto something. Turbo engines use different controls for the FPR since the intake is sometimes pressurized. It might be an issue with the FPR or something else in the fuel system like the fuel pump you mentioned. You might look into that before going for the ECU.

[Brad Ferguson]

thanks for all your replies. Sorry I haven’t replied recently I have been on holidays and haven’t been able to do any more diagnostics on the mazda. Also sorry for the long post.

I bought a new fuel pump and installed it. Fuel pressure now sits steady all the time and doesn’t fluctuate. Idle when warm is now really smooth and it is a lot easier to start when cold. But the bucking hasn’t changed. But still may have been a contributing factor but at least that is fixed.

While on holidays I started doing some research into engine management systems and what options I have out there. I am still researching and deciding at this point on which way I will go. a lot of it will come down to price and whether I can tune it by feel to get it running as the closest shop to me that can do dyno tuning is a little over 300km away for me. And I would prefer to install a system that I can get a basic tune out of for testing before towing it 300km to get it dialled in nicely.

But in the meantime I decided to get a wideband now, as I will need one with the aftermarket ECU for better quality tuning and they are always handy to have anyway. So I flew home yesterday for work and had a few spare hours before my lift arrived to pick me up, so I went ahead and installed the Wideband sensor and gauge. I bought the MTX-L innovate as it has wideband and narrowband outputs and datalogging capabilities.

After I installed everything, I calibrated and set it all up and fired the mazda up for the first time with the wideband. From everything I know about AFR’s on petrol vehicles stoic is approx. 14.7:1 and anything higher is lean and any number lower is rich.

I am getting numbers that don’t seem right to me. Which may be another contributing factor but I am still looking for a set of AFR maps for the stock computer just to compare to for now. After the engine starts, from cold, AFR is sitting around 11.2:1 with slow variations of 0.1 up and down, as I let the mazda warm up, just idling, the AFR slowly increase to 13.0:1. I left it until the thermo fan kicked in and engine was at running temps, and the AFR sat nicely between 12.92:1 and 13.11:1 at idle. I understand the richer start up is to help with firing the engine from cold and to help the engine warm up and keep idling.

I then took it out for a quick drive on medium acceleration the AFR would drop to 10.1:1 and would drive really well. come off the accelerator and the AFR would shoot up to off the scale which is 22.4:1 for this gauge, and when back at idle it still stays at 13:1. On hard acceleration and pulling boost the AFR would drop down to as low as 9.3:1 and that is around where the bucking/loss of power starts.

As I only had a short time before I left for work that is all the testing I have done so far, I will do more and more in depth when I get back home, as I only got 5 minutes of actual drive time.
But to me those figures seem WAY too rich, the last turbo I helped build the richest we were getting was 11.2:1 with a heavily worked engine.

Once I do decide and get the money spare I will get an aftermarket ECU for it, But could the higher compression engine be tricking the stock ecu into dumping in too much fuel and could this cause bucking from the torque loss from too much fuel in the air/fuel mix in the cyl’s? And also I only run 98 octane fuel from a reliable station. which I believe is the equivelant to 92/93 octane in the states.

thanks for your help and any more that can be offered

[Lorrin Barth]

Since the car is boosted I’m thinking it has a knock sensor. The glowing manifold, in my experience, is a sign of retarded timing. So, the knock sensor, for whatever reason, goes crazy and the ECU pulls timing to the point that unburned mixture is being exhausted to the manifold.

BTW. I was just looking at the AFR’s you listed and they are exactly what I would expect to see. Nothing wrong there.

[Matthew Molburg]

Extreme temps can be caused by improper air/fuel ratio, timing problems, restricted exhaust systems, malfunctioning O2 sensor, high boost levels or other engine control system problems.

Sounds like you’ve ruled out ECU issues and timing. I don’t think you mentioned any CELs. My Old 2004 Tacoma with a 3.4L supercharged V6 did this and it turned out to be a plugged up catalytic converter. My A/F ratio ran lean and it melted the cat internals and plugged it up, new cat no problem. Try pulling your O2 sensor out and see if that changes anything. Hope this helps.

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