MR2 Owners Club Forum banner
1 - 20 of 20 Posts

·
Premium Member
Joined
·
13,380 Posts
Discussion Starter · #1 ·
My 89 NA has an issue that recently appeared, and I'm struggling to figure it out.

Starting a couple of months ago, it will intermittently loose power / bog when trying to accelerate. It will run fine mostly fine for 10 minutes or so, then all of a sudden it starts running poorly. It seems both throttle position and RPM related. If you short shift at like 2500 rpm you can get up to speed and drive the car, but if you try to rev it up it just falls on its face. And when this issue is not occurring it feels like it may be a little down on power, but not bad.

So far I have replaced plug wires and plugs (it needed new wires pretty badly), as well as the cap and rotor. No change from that however.

Suspecting a fuel delivery issue, I installed a wideband that I have laying around (Innovate LC1). Idle and cruise shows 14.7:1. However at WOT it will initially go a little rich (like 13:1), and then go massively lean. Like 40:1. And that's when it's running "OK". This seems very odd, as I don't think it would even RUN at 40:1. And while it does feel down on power, I would expect it to barely run at that point. However when you let off it will slowly return to 14.7:1 (over maybe 5 seconds). So the wideband appears to be working properly. And the way it slowly comes back, it seems like it's loosing fuel pressure and then taking time to rebuild.

Seeing that I replaced the fuel filter (easy to do, and I had not done it since buying the car almost 10 years ago, so it was due). But no change.

I'm thinking fuel pump at this point... A fuel pressure gauge would be the way to test, except that I would have to install it so I could see it at WOT under load, which isn't so easy to do.

Thoughts?
 

·
Registered
Joined
·
958 Posts
I've seen a clogged fuel pump sock do this exact behavior. Basically the flow was really low, so as long as the fuel load was kept down, it ran ok-ish. Up the fuel flow demands and it just fell apart.

I guess a damaged fuel pump impeller could also do this, but usually it's a clog when things run badly at high fuel flow, but better everywhere else.
 

·
Super Moderator
91t gen5
Joined
·
6,910 Posts
To diagnose my fuel pump I used an amp clamp and oscilloscope. I found a repeated bad spot in the current wave form now I'm just trying to get the motivation to drop the tank. Of course this doesn't help if there is a flow restriction, I did use that same oscilloscope and a pressure transducer to monitor fuel pressure. The pressure seemed to keep up okay mid 30 psi but looking at min max values it would sometimes drop into the 20's.

My car used to spin the tires rolling in 2nd gear now it bogs at low rpm and slowly makes power but feels slow.

Or you could just replace the fuel pump because it's fun or at least help motivate me to do mine.
 

·
Premium Member
Joined
·
13,380 Posts
Discussion Starter · #4 ·
Here's another thought... The general lack of power feels like it's maybe running on 3 cylinders (it's that sort of power loss). The intermittent severe lack of power feels like it's running on 2.

What if it's a bad injector or two, or bad wiring to the injector(s). One injector not firing would certainly cause the wideband to report a much leaner condition than is actually present in the cylinders. And I can't help but think that if it was actually running 40:1 AFR, it would barely run, if at all. Currently it does accelerate at WOT, it just feels like maybe it's making 75hp instead of 110.
 

·
Registered
Joined
·
340 Posts
Does it shake when it's down on power? Running on 3 will cause a noticeable shake from the engine, something that's pretty obvious. Running on 2 will make it feel like the engine is going to fall out of the car above 2500 rpm.

Misfires and overly rich conditions will also appear as extremely lean. The O2 sensor is reading excess oxygen in the exhaust stream. If a cylinder doesn't fire, there's a lot of excess oxygen there for it to say lean.
 

·
Premium Member
Joined
·
12,237 Posts
...What if it's a bad injector or two, or bad wiring to the injector(s)....
On the early cars, it was common for the FI connectors to come loose intermittently. That is because the connectors were very fragile, and the locks would break off. It could be RPM dependent because it was sensitive to engine vibration. I would push the connector back on and the car would run fine for a while.

On the mk1b cars, the connectors were changed, so I wouldn't have expected that. Still a part of due diligence.
 

·
Premium Member
Joined
·
13,380 Posts
Discussion Starter · #7 ·
All right, unplugged and reseated the injector clips, and went for a quick drive this morning. Right from the start it was bogging and had no power. WOT in 2nd gear it wouldn't go over about 20mph, along with some bucking. Ease into it with partial throttle and it would get up to speed a little better. AFR still displaying in the 40:1 range at WOT.

Let it sit for a couple of hours, started it up, and immediately could tell it was running better. Drove it up and down the street again and it felt almost normal. Still felt like it was a little down on power, but not bad. And it can be hard to tell if a 110hp 4AGE is down on power when your other MR2 has 3x the power. AFR still reading about 30:1 at WOT though.

I'm liking @DefSport 's theory that it's a clogged fuel pickup, or maybe something in the tank that causes it to intermittently clog. Once it clogs the suction holds the clog in place, but letting it sit for a while might allow it to clear.
 

·
Moroccan Gold Imports
Joined
·
1,665 Posts
Sounds like you have it narrowed down to a fuel issue but it would be worth checking the timing as well.
 

·
Premium Member
Joined
·
13,380 Posts
Discussion Starter · #9 ·
I did check the ignition timing and it's right on 10 deg with T/E jumper in place (unless I'm reading the marks wrong, but I'm pretty sure the 4A marks are at 10 and 16, so it should be on the "middle" mark).

I have not verified cam timing, but the intermittent nature of it doesn't support that as an issue, as far as I can see.
 

·
Premium Member
Joined
·
12,237 Posts
Maybe one of the trigger pickups in the distributor is intermittent. The pickup coil needs to have continuity, and it also needs to be in correct registration to the trigger cam. If the shaft bearing was worn and the shaft became sloppy, that could cause the trigger cam to wobble out of the maximum clearance from the pickup. I imagine that would cause a fault code to store, though.
 

·
Premium Member
Joined
·
13,380 Posts
Discussion Starter · #11 ·
OK, I THINK I have ruled out the fuel pump... Sort of.

I managed to hook up a gauge to the fuel rail via the cold start injector hose, a custom made adapter, a piece of -3AN brake line, and another stack of adapters to the gauge which I zip tied to the engine lid. Yeah... a bit ghetto.

Fuel pressure was stable at high RPM / high load, even as the wideband was reading very lean. However, it was running "good" on this test drive (no bogging / major hesitation), so it's still possible there is a fuel component to that.

One thing I noticed is that it seemed that the lean AFRs begin about 4k RPM. This to me suggests an EGR or TVIS connection maybe?
 
  • Like
Reactions: rwheelz

·
Registered
Joined
·
9 Posts
This sounds a lot like the fuel problem I was having with my MK1. Clamping the fuel return line shut made my car drive normally. After a few minutes of hard test driving, I unclamped the return line and the car continued to drive perfectly until the next day when I had to clamp it again, drive around and unclamp it. It's been a few days and my issues still are gone. Pinching the return line shut and test driving can help you determine if the issue is upstream or downstream from the pump.

As for T-VIS, drive the car and bring the engine above 4350 rpm and you will hear a definite change in sound. You can also use a mirror to see if the T-VIS linkage moves while you rev it above 4350 rpm by hand.
 

·
Premium Member
Joined
·
13,380 Posts
Discussion Starter · #13 ·
Well, it seems I'm chasing two problems here. One is the intermittent bogging issue.

The other is that my wideband is a piece of junk! I hooked a multimeter up to the narrowband sensor, and at WOT while the wideband was reporting crazy lean (like 50:1), the narrowband was reporting .75-.8v, ie somewhat richer than 14.7:1. So that's good, and it matches up to my gut feeling that the motor wouldn't even be capable of running at 40+:1 AFR, let alone run reasonable well most of the time. As for feeling like it's down on power, I think that was a combination of a mis calibrated butt dyno, combined with the intermittent issue causing me to second guess how it was running the rest of the time.

SO, I think I just need to keep my fuel pressure gauge hooked up for a while and see if it drops when the intermittent issue comes back.
 

·
Registered
Joined
·
1,000 Posts
Sounds similar to the same issue symptom on early 90s GM crappy fuel injectors where the car would have intermittent start, run rich when cold. Would start n run idle noticeably better once warmed up.
I’m just taking a good guess here it could be sticking fuel injectors, high possibility that the solenoids copper winding is toast due to heat n age by now.
Hook up a decent oscilloscope to injectors and check the wave patterns cold and once warmed up at both idle and off idle should get interesting readings
 

·
Premium Member
Joined
·
13,380 Posts
Discussion Starter · #17 ·
Yeah, it could be AFM related. Will have to wait till the problem comes back to do any more real troubleshooting though.
 

·
Registered
Joined
·
194 Posts
Maybe the O2 sensor?? If the AFR is reading lean the sensor could be bad. Coud be a an exhaust leak close to the sensor as well. In which case your bogging issue would be a rich AFR. If you were kicking around 30:1 AFR the engine most likely would not run and if it did it would ping like crazy. If the car runs ok while it's warming up and then goes south when warm is the issue after the ECU goes into closed loop operation?

Pull your plugs and check deposits.

Pull the O2 sensor to see if it's clogged.

Check exhaust tip for heavy carbon deposits.
 

·
Registered
Joined
·
22 Posts
God, why do you guys always go for complicated stuff. Did you pull codes? It only takes a paperclip shorting between E1 and T in the diagnostic connector. Are you still running the vane air flow sensor? Did you check the accordion section of the intake between the vane airflow sensor and the throttle body? If you suspect an O2 sensor unplug it and drive the car. If it runs better the sensor is bad. Try that with the TPS as well. I've been a master tech for forty years and haven't driven anything but Toyota since 1978, including seven MK1 mr2's and I have yet to see a bad Toyota fuel pump. Knew a guy that replaced one in a Camry wasted $650 of the customers money. Open your eyes and look at the car it's probably something simple. Take the intake tube off the vane airflow and the throttle body and flex to make sure it isn't' cracked. Make certain you don't have a vacuum leak. I'd rather spend time than money.
 

·
Premium Member
Joined
·
13,380 Posts
Discussion Starter · #20 ·
Maybe the O2 sensor?? If the AFR is reading lean the sensor could be bad. Coud be a an exhaust leak close to the sensor as well. In which case your bogging issue would be a rich AFR. If you were kicking around 30:1 AFR the engine most likely would not run and if it did it would ping like crazy. If the car runs ok while it's warming up and then goes south when warm is the issue after the ECU goes into closed loop operation?

Pull your plugs and check deposits.

Pull the O2 sensor to see if it's clogged.

Check exhaust tip for heavy carbon deposits.
As I said already, it's NOT actually running lean, at least not most of the time. That was a red herring caused by a problem with my wideband sensor. And if you read the thread again, I questioned several times if it would even run at 30:1, which is what led me to compare the wideband to the narrowband. The stock narrowband o2 appears to be working fine.

The larger bogging issue is not temperature related. It's happened more often when hot, but I have had it happen with the car dead cold as well.

God, why do you guys always go for complicated stuff. Did you pull codes? It only takes a paperclip shorting between E1 and T in the diagnostic connector. Are you still running the vane air flow sensor? Did you check the accordion section of the intake between the vane airflow sensor and the throttle body? If you suspect an O2 sensor unplug it and drive the car. If it runs better the sensor is bad. Try that with the TPS as well. I've been a master tech for forty years and haven't driven anything but Toyota since 1978, including seven MK1 mr2's and I have yet to see a bad Toyota fuel pump. Knew a guy that replaced one in a Camry wasted $650 of the customers money. Open your eyes and look at the car it's probably something simple. Take the intake tube off the vane airflow and the throttle body and flex to make sure it isn't' cracked. Make certain you don't have a vacuum leak. I'd rather spend time than money.
Yes, I pulled codes. I had previously disconnected the TPS as well (while the bogging problem was actually occurring) which made no difference (forgot to mention that),. The only codes present were related to the TPS (I believe due to me disconnecting it).

No, I don't suspect the o2 sensor, since the problem primarily occurs at WOT where the o2 sensor isn't in use. Light throttle / low RPM cruise is fine. Also the sensor voltage looks good.

I suspect that I DO have a small vacuum leak actually, as I have trouble getting the car to idle at less than about 900rpm. But it has been that way for years, and has not changed recently. I have spent far too much TIME troubleshooting that idle issue over the years, and haven't made much progress on it (despite fixing a few vacuum leaks along the way).

Don't forget that the problem is extremely intermittent.
 
1 - 20 of 20 Posts
Top