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Hey guys, like the title says, I've got a 1984 GSL-SE that cuts out whenever the throttle is touched. I've searched the forums and found some second gen postings with mixed response but was hoping someone here had any ideas on it.
A week ago installed my RB header and removed my ACV along with the vacuum lines for it. Not sure if those are related to the problem, but everything was running perfect up until this morning. Overnight I'm not sure what happened but now whenever I touch the throttle the engine dies off. If I'm gentle it'll rev up to 2k but past that it just shuts off.
Things I've done:
Checked the fuel pump and confirmed running
Changed my fuel filter
Pulled out my injectors and cleaned them
It feels like it's ignition related and dies out exactly as if I turned off the key. TPS is working fine and is adjusted. Is there anywhere else in particular I should be looking? Other than the exhaust and hosing deletes the engine is stock.
Not trying to be a dick, and you said it was running fine after, but the -SE doesn't have all that much excess on the engine and what's there is there for a reason. The Air Control Valve makes sure you have fresh air into the exhaust when necessary to provide cooling and catalytic function. If you're still running cats, or even if not, it doesn't hurt to leave the ACV in place and operating.
Removing it may have opened up a significant air leak into the intake which can't be accommodated by the AFM anymore. much like removing the intake air pipe from the throttle body - it will be too much air bypassing the metering system for the ECU to calculate fuel and injector pulse properly. That's my guess.
When the ACV opens an air path other than thru the AFM, the AFM shutter door slams shut and the ECu thinks the engine shut down, killing fuel injector pulse.
Not trying to be a dick, and you said it was running fine after, but the -SE doesn't have all that much excess on the engine and what's there is there for a reason. The Air Control Valve makes sure you have fresh air into the exhaust when necessary to provide cooling and catalytic function. If you're still running cats, or even if not, it doesn't hurt to leave the ACV in place and operating.
Removing it may have opened up a significant air leak into the intake which can't be accommodated by the AFM anymore. much like removing the intake air pipe from the throttle body - it will be too much air bypassing the metering system for the ECU to calculate fuel and injector pulse properly. That's my guess.
When the ACV opens an air path other than thru the AFM, the AFM shutter door slams shut and the ECu thinks the engine shut down, killing fuel injector pulse.
Haha don't worry about sounding like a dick, everything helps! I used block off plate and gasket over the ACV port so I ruled that out but I'll stick it back on in the morning and see if that changes anything. Thank you!
As far as I'm aware the tank hasn't been cleaned. I went back and checked the fuel pump, found a bunch of crud in the cone filter insert.
Cleared that out and did a flow test. Flow looks about in spec but I'm pressure testing later today. The car idles fine on its own and will rev up when cold started or changed with the air adjust screw. Still only cuts out when the throttle is touched.
So I rented a fuel pressure kit and ran it through a couple different ways. These were with the pump jumper wire in and the car off:
At the fuel rail: 42 psi
At the fuel pump: 42 psi
At the fuel pump separated from tank: 42 psi
So pressure results were uniform and seem to rule out any sort of clog in the lines. Between tests it took a few seconds for the pump to prime and pressure to build back up. When I disconnected the fuel jump wire and was able to get the car the start and idle on its own the pressure dropped down and pulsed between 30-35psi. So I'm guessing this part is an issue at the pump. When the throttle is touched the pressure dropped immediately. Same result with the jumper wire in. Would a new pump help to solve this?
I went back to double check the fuel rail, there were no leaks at the injectors and the fuel pressure regulator looked fine. Fuel pressure went up from 42psi to ~60psi with the return line pinched.
Edit: Is it common for the pump to stop working all of a sudden instead of gradually? I've had a bit of vibration at high rpm (6000+) but attributed it to something being out of balance since it would keep revving to the top of redline no problem. Would that have been fuel cutting out/stuttering?
Last edited by klptk; 04-29-16 at 06:52 PM.
Reason: Clarifying fuel pump
Whelp looks like another (or maybe the only) problem is a vacuum leak (hoping this is the answer anyway). After putting the intake manifold back on a hissing sound started coming out louder. Car wouldn't even idle anymore. I pinched off the return line again to increase fuel pressure and it started up fine but still dies when the throttle is touched. I used a tube and my ear to listen where the hissing was and it was coming from the oil injector area. Took the manifold off again and went to check those hoses. As soon as I touched them they crumbled away. Looks like it's time to rebuild the nest....
Plugged the oil injector openings, put the manifold back on, still a hissing from either the air bleed socket or injectors themselves. Replacing all those bits tomorrow and will see where that leaves me.
42 psi seems kinda low. How did the pump perform with the volume test?
Volume test was fine with a stop watch and eyeball measurement got over 1600cc per minute.
I realize now that I tested the pump with a T-fitting connecting the line back to the fuel rail when it should have dead ended so that might explain the 42 psi (whoops). Of course now the gauge I rented is clogged but when I pressure tested it yesterday with the return line pinched it did go up to 60 psi so I suppose that means the pump is putting out enough pressure.
A vacuum leak would explain lower fuel pressure correct? Like I mentioned there's a hissing which I'm now noticing. The pressure regulator looked fine yesterday and didn't have any fuel leaking through the diaphragm. When I pinch the return line to bump up pressure the car will start and idle fine. Feathering up the throttle can raise the rpm up to about 2k but anything above that and it shuts off. I guess I'll find out tomorrow when I replace all the hosing with silicone.
I decided to recheck my throttle sensors. TPS is working fine and double checked with a backup I have. AFM also looked good after testing the resistances.
Problem solved. I replaced a few things so I'm not sure which one exactly fixed it but she's back up and running. Life is happiness again
Replaced all the vacuum hoses
New fuel pressure regulator
New injector seals and grommets
New dizzy cap/rotor/plugs
Sorry I couldn't really pinpoint which of those things did it but thanks guys for the help!
Edit: Well it was okay for about ten minutes. Got everything together, idled normal for about five minutes. I wanted to go for a quick test drive and about ten blocks down the road the same thing happened. Towed it back to my house and tested compression. Both rotors were bouncing up to about 115psi. It's been a long week and I really don't want to keep throwing money at this.
Last edited by klptk; 05-05-16 at 12:44 PM.
Reason: Nevermind.
Keep looking at that filter insert at the pump,doesn't look real good. Comment about rented gauge being clogged, With what,same as the filter pic you posted? Not my car& not there to put eyes/hands on it but think you need to address fuel supply from tank forward. My thoughts are not enough pressure and certainly not enough volume to feed the engine at anything more than an idle and any kind of load. Suspect you have rust/debris in pump,supply lines. You've had several of fuel feed connections open already,any signs of gunk in parts that were removed or in the fuel lines that you could see? Possible that you removing/cleaning the prefilter allowed just enough fuel to get the car to start and idle somewhat normally,driving it dislodged? more stuff to plug things up again. Most of the parts you replaced were maintenance items and likely had no effect on problem. When you say you cleaned the injectors,what did you use and what came out? Take that old pressure regulator and over a clean paper towel tap and bang it on a table or bench and see what comes out for evidence. I restore old cars and motorcycles and your symptoms are that of fuel system contamination, very common on antique machines,ours RX7s being 30+yrs old now. There are numerous threads on this site describing the contents of gas tanks removed from cars with driveability problems. I've read thru your thread and seen some of the testing that was done. One piece of advice: start with the simple things first and rule them out for certain and then systematically move on to more complex things There is the KISS philosophy, very easy to start chasing your tail with problems like this. Diagnostics doesn't cost any more than your time & certainly cheaper than replacing parts. Used up enough bandwidth with this reply,hopefully some food for thought. You may pm me for some guidance with this,be happy to help.
**** Edited to add: I think I may have found your problem!****
(REMOVED - as I think it's bad information looking at the FSM diagram for the Fuel Rail)
^If that doesn't fix it - I agree with this guy above - sounds like fuel system.
I would remove the lines at the pump and fuel rail (easy enough, as both feed and return run right next to the firewall) and blow them out thoroughly - being careful to catch what comes out. If you find rust, you have a restriction in the line preventing adequate fuel flow for anything more than an idle.
Could also be the high pressure, fuel injection filter (rear, by the pump) is clogged preventing flow, or a bad fuel pump.
Those other things can't hurt - but by the simple fact that it ran correctly for 10 minutes, you did something that freed up flow, whether it was the Fuel Pressure Regulator or something on the fuel rail when you did the injectors.
Long shot: check your fuel pressure hoses all around. I've seen one that eroded on the inside allowing a flap of rubber to occlude the hole, making for a VERY hard problem to find. Replacement of the hose fixed the problem, and then I cut it open to find the flap of rubber acting like a valve in there. Good luck,
Keep looking at that filter insert at the pump,doesn't look real good. Comment about rented gauge being clogged, With what,same as the filter pic you posted? Not my car& not there to put eyes/hands on it but think you need to address fuel supply from tank forward. My thoughts are not enough pressure and certainly not enough volume to feed the engine at anything more than an idle and any kind of load. Suspect you have rust/debris in pump,supply lines. You've had several of fuel feed connections open already,any signs of gunk in parts that were removed or in the fuel lines that you could see? Possible that you removing/cleaning the prefilter allowed just enough fuel to get the car to start and idle somewhat normally,driving it dislodged? more stuff to plug things up again. Most of the parts you replaced were maintenance items and likely had no effect on problem. When you say you cleaned the injectors,what did you use and what came out? Take that old pressure regulator and over a clean paper towel tap and bang it on a table or bench and see what comes out for evidence. I restore old cars and motorcycles and your symptoms are that of fuel system contamination, very common on antique machines,ours RX7s being 30+yrs old now. There are numerous threads on this site describing the contents of gas tanks removed from cars with driveability problems. I've read thru your thread and seen some of the testing that was done. One piece of advice: start with the simple things first and rule them out for certain and then systematically move on to more complex things There is the KISS philosophy, very easy to start chasing your tail with problems like this. Diagnostics doesn't cost any more than your time & certainly cheaper than replacing parts. Used up enough bandwidth with this reply,hopefully some food for thought. You may pm me for some guidance with this,be happy to help.
I've been over complicating it a lot since this has been my only DD and I spent the last week or so bumming rides off friends and family. Luckily my second car is back up and running so I'm not in such a rush anymore to finish up the 7.
The picture of the pre-filter was while I was cleaning it out. It was spotless before putting it back in. The injectors were just wiped the outside clean and sprayed the filter side with a quick shot of brake cleaner. Nothing really came out besides a bit of browned backwash. I replaced the grommets, seals, and pintle caps before putting them back. I have a second set of SE injectors that I'll send out to be fully serviced. No debris in the old FPR either.
I've gone back and started looking at my fuel lines. So far I've looked at all the hoses from the exit side of the fuel pump to the end of the fuel return hard line (rain came and I had to call it quits before checking the pump pre-filter again). There wasn't any rust or debris and blowing through them didn't feel like there was any blockage on that side of the pump but it looks like there was a fair bit of water in the system. I guess I should drain the tank right?
Originally Posted by LongDuck
**** Edited to add: I think I may have found your problem!****
In looking at your first picture, your fuel rail is setup incorrectly. The Fuel Pressure Regulator (FPR) should be at the FRONT of the rail facing the front of the car. Your Fuel Feed and Return lines are in the correct position - so leave them that way, but the problem is that the FPR is hooked up BEFORE the injectors, not after where it belongs. Thus, when you supply vacuum to the FPR (*like when you hit the gas and increase intake plenum vacuum), it shunts flow going into the rail - killing pressure at the injectors, and killing your engine. Mounted correctly at the front of the rail, that vacuum source under acceleration will shunt the flow at the Fuel Return to INCREASE fuel pressure on the rail, increasing injector pressure during acceleration.
To fix it - remove your Fuel Rail again, remove the FPR and that blue anodized bolt head you have and swap their positions. This will put your FPR where it belongs, then attach the vacuum line to it coming from the vacuum line spider. Reconnect your Fuel Feed and Return hoses as you have them now.
DON'T CHANGE ANYTHING ELSE, and report back with findings. I just went out in my garage at 1/2 past midnight to confirm all this - so have a look and let us know what you see!
^If that doesn't fix it - I agree with this guy above - sounds like fuel system.
I would remove the lines at the pump and fuel rail (easy enough, as both feed and return run right next to the firewall) and blow them out thoroughly - being careful to catch what comes out. If you find rust, you have a restriction in the line preventing adequate fuel flow for anything more than an idle.
Could also be the high pressure, fuel injection filter (rear, by the pump) is clogged preventing flow, or a bad fuel pump.
Those other things can't hurt - but by the simple fact that it ran correctly for 10 minutes, you did something that freed up flow, whether it was the Fuel Pressure Regulator or something on the fuel rail when you did the injectors.
Long shot: check your fuel pressure hoses all around. I've seen one that eroded on the inside allowing a flap of rubber to occlude the hole, making for a VERY hard problem to find. Replacement of the hose fixed the problem, and then I cut it open to find the flap of rubber acting like a valve in there. Good luck,
On all the diagrams I've seen the FPR is on the rear facing side of the fuel rail. I did the banjo bolt to get rid of my pulsation dampener but that hasn't given me any problems over the last year and a half. I'll still switch their positions though to see if that solves it. Otherwise I can try to dig out the old PD and try with it back on.
Damn - I think you're right now that you're showing the FSM diagram. Sorry to point you in the wrong direction; I'd leave it the way it is.
Why did you remove the pulsation dampner? These are used in pairs (one on the Fuel Pump banjo - one at the Fuel Rail) in order to reduce fluctuations in fuel pressure.
Damn - I think you're right now that you're showing the FSM diagram. Sorry to point you in the wrong direction; I'd leave it the way it is.
Why did you remove the pulsation dampner? These are used in pairs (one on the Fuel Pump banjo - one at the Fuel Rail) in order to reduce fluctuations in fuel pressure.
Back when I first got the car I was smelling gas in the engine bay. People said it was an early sign of the PD failing and I didn't have the money to replace it but I also didn't want to keep it and risk a fire so I just used the bolt and it got rid of the smell.
Pulsation dampner failure is more common in 2nd gen cars, not ours. Mazda chose to put one on the fuel rail for a reason. Hoping someone will come along and confirm or deny whether it's necessary to ensure reliable function. For the cost, I would think it's cheap insurance at this point.
Pulled the tank today to check the pickup tubes. A lot cleaner than I expected it to be! Fuel wise this only leaves the injectors and pump as suspects.
Pulled the tank today to check the pickup tubes. A lot cleaner than I expected it to be! Fuel wise this only leaves the injectors and pump as suspects.
Put in a new fuel pump and am certain it's not the injectors so now I'm back to chasing the air leak I heard earlier. With the car running, quickly opening and shutting the throttle made a baby bov sound underneath the intake manifold.
I saw on other forums people blowing air and smoke in to much success so here's my take on it. A trip to Ace and ten bucks later I got this little beauty put together. A cheap bicycle pump, PVC end cap, threaded barb, and about a foot of latex tubing. Boy is it easier to hear without the engine running!
Tomorrow I'll get some dry ice to push through and find the hole. Just by ear it's coming out around the front rotor injector. Grommets were replaced so I'm set on the LIM to engine seal.
So this time it looks like it's actually fixed! Turns out it was the lower intake gasket. When I pulled it off it was soaked, bubbling, and hand a colony of dead spiders stuck to it... Spent two days scraping off old baked on gasket material and got it back together this morning. She runs like a champ and was perfect on my test run. Definitely recommend giving the bike pump tool a shot for any vacuum leaks. Thanks for the input everyone!
This is the lower intake manifold to engine gasket, correct? I wouldn't have expected that would be enough of a vacuum leak to cause the engine to die. Was it soaked with gasoline from injectors leaking down?
Was hoping you'd post back after all the above. Glad you got it fixed,
This is the lower intake manifold to engine gasket, correct? I wouldn't have expected that would be enough of a vacuum leak to cause the engine to die. Was it soaked with gasoline from injectors leaking down?
Was hoping you'd post back after all the above. Glad you got it fixed,
Yeah air leaking from the top of the center iron where the vacuum line comes out by the injectors. New gasket seems to have done it though. I'm sure gasoline had a lot to do with it but there was also some darker (oil?) fluid behind it in the circles above the rotor housing studs.
04-28-16, 09:25 PM
