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Discussion Starter · #1 ·
Hi this is my first post on the forum, I’m pretty new to working on cars and only started because after I bought this car it stopped working and the shop I took it too only made it worse.

So the problem was that it wouldn’t start or would start and then immediatley stall. We ruled out vacuum leaks and spark plugs so ruled it out to fuel. The shop stated they dropped the gas tank and replaced the “broken” fuel level sensor. When I got it back the spark plug wires were taped with numbers but were mismatched so it was misfiring like crazy and wouldn’t stay on. They told it I had low compression - so worn piston rings or head gasket, anyway once I’m home it leaks gas all over my garage and I check and its the fuel line leading the filter. So here’s where I started attenpting to fix it, I replaced the spark plugs just in case, replaced the pretty worn spark plug wires, replaced the air filter, fuel filter and oil filter as well as an oil change. It finally began starting after I replaced the fuel filter which leads me to believe even more that it’s a fuel problem. My next question is, with the car starting and idling ok not too rough but not perfect should I next attempt to clean the fuel injectors or replace the fuel pump?
Any opinions help, thanks!
 

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...So the problem was that it wouldn’t start or would start and then immediatley stall. We ruled out vacuum leaks and spark plugs so ruled it out to fuel...
You didn't mention timing. If the car starts, you should certainly check spark timing. There is also valve timing to worry about. A car that will start but not rev up is characteristic of a timing belt that is a tooth off. That doesn't mean that this is the problem, but if you can't find something else, you will need to check this. If your fuel pump runs, then it is probably not the problem. Limited fuel feed does not become apparent until you get to high engine load.

Does the car idle at all? You are not clear about this.. If the car doesn't idle, then you should try jumping out the crash interlock on the fuel pump. Fp to B+ or something like that. Then the fuel pump will run with the ignition on, and you will be able to eliminate that as a cause.
 

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'91 MR2 Turbo, '20 BRZ
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Interesting, as I've never had to drop a MKIa/b fuel tank to replace the fuel level float & empty sensor. That can be done in the cabin my removing the center console. A LOT more work to drop the tank, and clearly they weren't competent in that either. Yikes!!

So when they told you it had "low compression" what were the actual compression numbers? BGB states comp should be (ideally) 179PSI, with only a 14psi difference per cylinder, and 142PSI as the minimum. If numbers are below the min or WAY low on a cylinder or two, that could cause difficulty running. One cylinder down, it'll still run, just won't accelerate well at all. Even if ONE injector stopped working and only running on 3 cylinders, it'll still run... Yet when you are low or don't have 2 cyl operational, then yeah it's not going to want to run. So get those numbers and report back.

I really doubt injector(s) are the issue, but you can remove them fairly easy to check. If the fuel pump runs (Fp to B+ in diag connector as RM said) I doubt it's your problem either. Honestly, if I was the shop and dropped the tank, I'd advise spending the 27-40$ and replace the pump and filter....

Next, if the comps are OK, and fuel pump running, and you can hear the return line pushing fuel back to tank, then it's down to ignition. As RM said, verify timing is OK per BGB (distributor CAN move if not locked down well during plug wire changes). Then ensure you have spark in all plugs (I just use a timing light and move the inductor sensor to each plug.) I would also rotate the engine to Compression TDC and check all your timing points, from the crank pulley to the cam gears, and ensure the cams aren't off vs. crank.
 

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Discussion Starter · #4 · (Edited)
Interesting, as I've never had to drop a MKIa/b fuel tank to replace the fuel level float & empty sensor. That can be done in the cabin my removing the center console. A LOT more work to drop the tank, and clearly they weren't competent in that either. Yikes!!

So when they told you it had "low compression" what were the actual compression numbers? BGB states comp should be (ideally) 179PSI, with only a 14psi difference per cylinder, and 142PSI as the minimum. If numbers are below the min or WAY low on a cylinder or two, that could cause difficulty running. One cylinder down, it'll still run, just won't accelerate well at all. Even if ONE injector stopped working and only running on 3 cylinders, it'll still run... Yet when you are low or don't have 2 cyl operational, then yeah it's not going to want to run. So get those numbers and report back.

I really doubt injector(s) are the issue, but you can remove them fairly easy to check. If the fuel pump runs (Fp to B+ in diag connector as RM said) I doubt it's your problem either. Honestly, if I was the shop and dropped the tank, I'd advise spending the 27-40$ and replace the pump and filter....

Next, if the comps are OK, and fuel pump running, and you can hear the return line pushing fuel back to tank, then it's down to ignition. As RM said, verify timing is OK per BGB (distributor CAN move if not locked down well during plug wire changes). Then ensure you have spark in all plugs (I just use a timing light and move the inductor sensor to each plug.) I would also rotate the engine to Compression TDC and check all your timing points, from the crank pulley to the cam gears, and ensure the cams aren't off vs. crank.

Car does idle sorry for not being clear it’s just a little choppy but otherwise sounds normal.


Exactly what I thought as I took out the center console plastic piece and removed the the metal plate. Funny thing is the screws to the metal plate was loose as can be almost falling out and the float sensor itself was only secured by three screws. I don’t remeber the exact numbers but they ranged from 160, 120, 90, 90. I want to mention I believe they pulled those numbers out of nowhere because I was under the impression to complete a compression test you had to get the sensor pretty far in the engine and not just at spark plug level 😂. With 60k miles I didn’t think it was something super serious which is what they were implying.

I’m sorry for the lack of clarity but when idling if I press the gas hard it struggles and sounds rough and immediatley goes up to 2k rpm then goes back down, if I slowly press however it revs like normal until about three where it stops and sputters like before. I’m not sure if this forum allows videos but I can try to upload a clip if possible.

In conclusion as soon as I get home from work I’m going to try those tests to rule out a few more things including the fuel pump, and secure the floating gauge properly, let me know if anything I said clears anything up and or if I should try something different, thanks!
 

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I wish you luck. It's hard to find a competent shop nowadays, or at least one that doesn't try to gouge you. While there are more "modern" methods of doing compression test, those that measure pressure from the spark plug area are often good enough for general numbers. I use that method all the time for my own vehicles. I ALSO do leak down tests when the comps are low to see what may be contributing to the low compression, be it rings, head-gasket, piston, etc... If the numbers taken in this way were indeed 160, 120, 90, 90, then that would indeed indicate a problem. So my advise, grab a comp tester for yourself, and repeat the test on your own.

By your description, the fact that if you slowly increase the throttle and it's OK, it could indeed be a fuel issue. Any time you suddenly hit the throttle, there is a moment where there is a lot more air coming in, and the AFM / TPS indicate this to the ECU and then it opens the injectors up more. When they increase suddenly, if there is not good fuel flow, it can struggle. The opposite can also be possible, whereby the system dumps TOO MUCH. Black / carbon like smoke from the tail pipe usually indicates the latter.

So I would double check the AFM, and the TPS as well. NOTE: I hope for your sake, the techs didn't mess with the AFM and unplug it the wrong way... though I don't know why they'd have touched it for the work stated.
 

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Discussion Starter · #7 ·
I wish you luck. It's hard to find a competent shop nowadays, or at least one that doesn't try to gouge you. While there are more "modern" methods of doing compression test, those that measure pressure from the spark plug area are often good enough for general numbers. I use that method all the time for my own vehicles. I ALSO do leak down tests when the comps are low to see what may be contributing to the low compression, be it rings, head-gasket, piston, etc... If the numbers taken in this way were indeed 160, 120, 90, 90, then that would indeed indicate a problem. So my advise, grab a comp tester for yourself, and repeat the test on your own.

By your description, the fact that if you slowly increase the throttle and it's OK, it could indeed be a fuel issue. Any time you suddenly hit the throttle, there is a moment where there is a lot more air coming in, and the AFM / TPS indicate this to the ECU and then it opens the injectors up more. When they increase suddenly, if there is not good fuel flow, it can struggle. The opposite can also be possible, whereby the system dumps TOO MUCH. Black / carbon like smoke from the tail pipe usually indicates the latter.

So I would double check the AFM, and the TPS as well. NOTE: I hope for your sake, the techs didn't mess with the AFM and unplug it the wrong way... though I don't know why they'd have touched it for the work stated.

Just secured the screws that were lose and for the floating sensor and my gas gauge is fixed… yay! anyway I decided to upload two short clips of the sound after I tightened it up because I’m not too good at explaining it. On my way right now to borrow my friends compression tester, let me know if the sound clips help.

Fast Gas Pedal Press - 1985 Toyota MR2 Fast Gas Pedal Press Issue

Slow Gas Pedal Press - 1985 Toyota MR2 Slow Gas Pedal Press


Thankfully no black smoke and car idles pretty smooth.
 

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I would bet that you have low fuel pressure. Not enough enrichment for a quick throttle opening. Dead head a pressure gauge on the fuel line. You need to see 50 PSI. Regulated press in the 47- 48 PSI range with the vac line removed.
 

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Discussion Starter · #9 ·
I would bet that you have low fuel pressure. Not enough enrichment for a quick throttle opening. Dead head a pressure gauge on the fuel line. You need to see 50 PSI. Regulated press in the 47- 48 PSI range with the vac line removed.
Thanks for the clairification that’s also what I thought after it began starting once replacing the filter. considering it had no prior issues pretty decent milage and it now starts idles and slowly throttles pretty well to about 3k rpm I would say I’ve almost corrected all the damage they have done unless I find more. I will get back with fuel pressure results after work today.

On another note where is the shrader valve located on the mk 1, I was going to use a standard fuel pressure test but didn’t know where to find the test valve.
 

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... You need to see 50 PSI. Regulated press in the 47- 48 PSI range with the vac line removed.
Misleading. Remember that the fuel pressure is regulated relative to the manifold vacuum. The spec from the '86 BGB is 33-40 psi with the engine stopped or the vac line disconnected, and 24-31 psi at normal idle.
 

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... where is the shrader valve located on the mk 1, I was going to use a standard fuel pressure test but didn’t know where to find the test valve.
There is no test valve. The usual place to tap in for a fuel pressure test is the port for the cold start injector. You would want to replace the crush washers unless you are feeling lucky.

Unlikely that the problem is fuel pressure. As long as the engine idles, a fuel deficit will usually not show up until you get the throttle well open. For example, if the engine stumbles at full acceleration or misfires on a climb.
 

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Discussion Starter · #12 ·
There is no test valve. The usual place to tap in for a fuel pressure test is the port for the cold start injector. You would want to replace the crush washers unless you are feeling lucky.

Unlikely that the problem is fuel pressure. As long as the engine idles, a fuel deficit will usually not show up until you get the throttle well open. For example, if the engine stumbles at full acceleration or misfires on a climb.
Check above sound clips, those along with your description of a fuel deficit matches almost perfectly what happens on my car on a slow climb and full throttle, which leads me to believe even if it’s not a fuel pressure issue I think it’s a fuel problem.

As for the pressure test port thank you for clearing it up!
 

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Discussion Starter · #13 ·
Hi, just checking in went under the car earlier when I was replacing the brakes and noticed the exhuast manifold, I’m not sure if it’s a casing or shell, was torn open on both sides and looked damaged, I also looked up symptoms of an exhaust leak and it fits my lack of power issue. Is this as serious as I think or is this just a casing or shell for the pipe?

Automotive tire Reptile Gas Scaled reptile Motor vehicle
 

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That's the heat shield.

There is sign of carbon there, indicating a leak. There's 2 rings used as gaskets and they don't last forever, get hard brittle and shrink.

Easy job to replace the gaskets, i like to smear loctite ultra copper goop generously on both sides before assembly. Hard part is getting those 3 nuts off at the flange. You're going to want to soak those mofo's with penetrating spray like wd40 or something. And work them slowly.
 

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There is a switch in the TPS that tells the ECM the throttle plate is closed and the car is at idle. If the switch is shorted it will idle all day long but will not rev. This will happen even if there is water in the TPS plug. Try unplugging the TPS and starting it. Then try blowing out the plug and the TPS to remove any moisture. If you have access to a wiring diagram and a DVOM back probe the two wires for the switch. With the throttle plate closed you should see continuity. Then open the throttle and continuity will go away. If it doesn't that's your problem, replace the TPS.
 

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Discussion Starter · #17 ·
Hey sorry for the lack of updates I got too caught up to post.

Awhile back after the exhaust post and the sound clips I decided to drain the tank through the drop sensor in the center console. While draining I noticed….the gas tank was full of rust! Particles, rocks everything you could imagine, so I assumed it was blocking my fuel filter and my replacement if it earlier was a temp solution. Anyway, dropping the tank was a bitch, but I did got new hoses and clamps and whatnot, and used some rust remover + degreaser and then sealed the tank with a gas tank sealant and let it dry. While I was in there I replaced the fuel pump as well.

So after fixing my two leaks after the reinstall, it started and power to my gas pedal was back, i waited for my RPM’s to drop ( smooth idle) and managed to get up to 5k RPM, so I’m assuming I did something? Anyway I wake up the next day start it and I believe I still have low fuel pressure somewhere because it now acts the same as it did before. If my issue keeps fluctuating but recats everytime I do a fuel related fix I would think it would have to be fuel. To top it off I took out the spark plugs and two were black, (i replaced them a week ago). I’m stumped I keep finding more and more things this shop did wrong, it’s just another reminder to go to a trustworthy mechanic or fix it twice.
 

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.... used some rust remover + degreaser and then sealed the tank with a gas tank sealant and let it dry. While I was in there I replaced the fuel pump as well.
Yeah I'm going through the same hell right now. Though my engine is out which makes removing the tank a bit easier. Curious to see which tank cleaner/sealer system you went with. I did the KBM, and found it to be a pain on the sealing step getting it to coat everything due to baffles, tubes, and bowl! Still looks like it covered MOST of the stuff on mine.

It's interesting, that right after the replacement, it ran, idled, and rev'd ok... Yet very strange that the next morning all went to heck again!! I'm trying to think, of the act of disconnecting fuel lines, and changing out the fuel pump alone, would do to Temporarily help. It's almost like there is a clog/restriction somewhere, inconsistency in the system building pressure, or too rich?

Have you gone through all the fuel lines, both to and from the fuel rail and ensure they are clean? Have you popped out the fuel injectors to see if there is any debri? My concern, is if there was notable rust getting through the system, and past the filter, it may still have some present in the lines. Next I would double check that the fuel pressure is reaching the BGB spec'd psi.

Finally you noted two plugs were black...like flat black, or OILY/shiney black? Flat black would actually indicate running TOO RICH. In which case I'd clean the injectors, and verify everything that contributes to the fuel map is checked. (AFM, Coolant Temp Sensor, TPS, etc..)
 

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Discussion Starter · #19 ·
Yeah I'm going through the same hell right now. Though my engine is out which makes removing the tank a bit easier. Curious to see which tank cleaner/sealer system you went with. I did the KBM, and found it to be a pain on the sealing step getting it to coat everything due to baffles, tubes, and bowl! Still looks like it covered MOST of the stuff on mine.

It's interesting, that right after the replacement, it ran, idled, and rev'd ok... Yet very strange that the next morning all went to heck again!! I'm trying to think, of the act of disconnecting fuel lines, and changing out the fuel pump alone, would do to Temporarily help. It's almost like there is a clog/restriction somewhere, inconsistency in the system building pressure, or too rich?

Have you gone through all the fuel lines, both to and from the fuel rail and ensure they are clean? Have you popped out the fuel injectors to see if there is any debri? My concern, is if there was notable rust getting through the system, and past the filter, it may still have some present in the lines. Next I would double check that the fuel pressure is reaching the BGB spec'd psi.

Finally you noted two plugs were black...like flat black, or OILY/shiney black? Flat black would actually indicate running TOO RICH. In which case I'd clean the injectors, and verify everything that contributes to the fuel map is checked. (AFM, Coolant Temp Sensor, TPS, etc..)

Flat Black Spark Plugs for the two that were dirtier, it was also my assumption i was running to rich because my exhaust heat shield is basically melting to im running a little hot i think 😭. I haven’t done anything else fuel related haven’t checked the lines or injectors, I’m going to do that tonight, and might just replace the injectors all together so that I don’t have to worry about if I cleaned them the right way and replaced the right seals.

As for the gas tank sealant, I can find the name in a second but I got it from Summit Racing, after the tank was clean I let it roll around and like you ALMOST coated everything, but i think it got majority of the loose rust at the bottom and in the baffles so I think that issue is fixed. Quick reminder though when you let the sealeant dry i found it hard to avoid strings in the sealant or bubbles. But after drying for a while you should be good.
 
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