You know what’s really hard? When you think you have finally reached your goal but it turns out to be the beginning of just another struggle.
So yeah, I did put the engine together. I did manage to fire it up. It didn’t explode. But that wasn’t enough to satisfy me, my relentless naivety also made me expect that this engine, built by someone who never built an engine before, is going to run perfectly as if from factory right off the bat. Guess what, it didn’t, and guess what I had the nerve to be pissed off about it. Why do I always amaze myself in retrospect? Do I really become that much smarter everyday that I seem so unbelievably stupid every time I look at myself in the past.
After the first wave of excitement which was blurring my capability to actually asses the car started fading out I could finally realize that the car wasn’t running as I think it should be.
Completely exhausted with wrenching and only yearning for driving pleasure I somehow forced myself to go back to wrenching and figure out what is wrong. To make sure the car really was running poorly and was low on power I had a small “race” against my daily driver a 107 hp Suzuki sx-4, which does 0-60 in 10 and something seconds. Something an Mr2 mk1 should be able to cream in fully stock form, not to mention with my uprated cams and raised compression.
As I feared my wife behind the wheel of the Suzuki left me eating dust sitting in my “sports car” watching a family friendly cross-over disappear into the horizon. Well it wasn’t quite as cheesy and dramatic as that, but the Suzuki was obviously faster. This defeat was a clear ticket to the garage for the MR2.
Thankfully I did find out and sort my problem, but I won’t tell you what it was just yet, I will sinisterly force you to through go through more piles of boring text to find out. So here’s a list of things and tips that you should probably first take a look when attempting to diagnose what’s wrong with your engine.
Spark plugs are great bang-for-back item in terms of diagnosis. They are super easy to remove and can tell you a lot about what might be wrong with your internal combustion bundle of joy.
Here’s a little chart that can help you diagnose your spark plugs in case they don’t look normal.
Fuel pressure can go out of spec because of any of the following: leaky injector o-rings, faulty injectors, dying fuel pump. Fuel pressure is also relatively easy to check. Check the pages from the BGB to see exactly how to do it. Fuel pressure for a 4age 16v should be 38 to 44 psi (265-304 kPa).
Air Flow meter
If everything checks out fuel-wise I would take a look at the air flow meter next. Checking it out is super simple, just rip out a multimeter and measure the resistances. Make sure you are measuring using the correct resistance setting and also make sure you’re multimeter is zeroed in case it’s an analog one. Zero it in by touching the probes together and turning the knob until the dial hits zero. Zero in for the resistance setting you will be using. Here are the pages from the workshop manual you need.
Throttle body position sensor
Same deal as the Air flow meter. Get out the multimeter and test. You need a thickness gauge for this fellow too. This can be done on the car but it’s a lot easier if you actually take the throttle body off.
Correct ignition timing is critical for making power and running right. Ignition timing determines when spark occurs in relation to the position of the piston. In case its wrong you can have incomplete combustion, knocking and other stuff you don’t want. Ignition timing is checked with a timing light. In case of the 4a-ge the procedure is as follows (video below too):
- Make sure engine is at operating temperature
- Attach timing light (watch video below to see how)
- Connect diagnostic plugs E1 and T
- Fire up engine
- Point timing light at timing marks.
- Timing needs to be 10 degrees before top dead center (BDTC) i.e. advanced for the 4A-GE 16v
Cam timing is not to be confused with ignition timing. Cam timing determines the position of your camshafts and your valves in relation to the position of your pistons. How do you check cam timing? Easy. Camshaft pulleys and crankshaft pulleys all have TDC marks on them that need to align with TDC marks on things right behind them.
Cam pulleys align against the backing plate, crankshaft pulley aligns with the bottom timing cover (corolla 4age) or with the pointer needle (MR2 4age) and the timing belt sprocket aligns with a mark on the oil pump (you need to remove crank pulley and timing cover to see this).
Lift up your car, remove the passenger side-rear wheel, remove the top timing cover, rotate engine by hand until crank pulley is at TDC. In case any of your cam timing pulleys is not at TDC when your crank pulley is, your cam timing is off and that will make your engine run like poop.
What was wrong in my case?
Did you scroll down to this heading right away? How naughty.
MY timing belt skipped a tooth. How did I find out? By looking at my cam timing. When I put my crank pulley at TDC neither off my cam pulleys were at TDC. This clearly told me something was off here.
What failed? A 30 year old tensioner pulley spring couldn’t do its job. I could not tighten the tensioner pulley sufficiently and my belt skipped a tooth. I tried it twice and twice it skipped. Solution? Got rid of it, pushed tensioner pulley in manually and tightened it down. Worked like a charm. A whole nother car now.