'96 4Runner delayed hot start problem...

mabrodis · 07-22-2006, 10:35 AM

Greetings, we are trying to diagnose a problem on a '96 4Runner, 3.4L V6, not a Tacoma I know but we're grasping at straws here trying to find some guidance...crossposted also (and on 2 other Toyota forums, with no magic answers yet)...

The engine runs fine normally, occassionally gets a "Fuel Trim too Lean", which (if I'm reading things right) means it's actually running rich and the trim has maxed out whatever leaning it can do...however, the real problem is after running the engine until up to normal temp, then shutting it off, it will start again within about 15 minutes with no problems, but if you wait till after 15 minutes the vehicle will not start, until about an hour later when things have cooled down more apparently.

While it's cranking and not starting, it's sputtering and sounds like it's trying to start but just not quite there (sometimes it will even run for a few seconds at about 300rpms then die), firing, backfiring, etc, but never actually gets going. You can, however, start it by spraying starting fluid into the throtle body and it will fire up, makes a horrible pinging noise for a few seconds and then idle normally, however, while it's idling, it's still not all there, if you rev it up it will not rev up normally, will hit about 2500-3000 rpms and just stay there for about 5-10 seconds, apparently (as best I can tell only because it kinda 'feels' like that) because there is no more fuel to rev any higher. After the 5-10 seconds it will rev and drive normally.

We installed a fuel pressure guage on the fuel rail so with the hood open we can monitor pressure and while cranking the engine (when it won't start) the pressure shown is 21psi, very consistent. However, when the engine is cold and doing short cranking bursts (so it won't start, just to see what the pressure is when you know it will start if you want it to) the pressure is also 21psi. As soon as the vehicle starts idling the pressure shown climbs to 34-35psi. If you rev the engine you see the pressure drop down to maybe 27-28psi and then climb back up as it calms down. (I say "pressure shown" because the gauge is a new B&M fuel gauge, so should be accurate, but I wouldn't bet my life on it)

We replaced the fuel pressure regulator (back side of the fuel rail) last night and that unfortunately didn't fix a thing. We have a fuel pump ready to go in and can put that in. The fuel pressure numbers we were reading from Toyota's documents of normal idling pressure of 32-36 (I believe, going by memory here) and if you disconnect the vacuum line off the fuel pressure regulator it was sposeto go up to about 38-44psi...on this vehicle disconnecting the vacuum line to the regulator did absolutely nothing, didn't change the pressure in the fuel rail at all, and we have never seen fuel pressures in the 38-44psi range at anytime when running.

So do those numbers sound right at all to anyone? The problem I see is if the fuel pump can put out 34-35psi, like it's doing while the engine is idling, why isn't it doing that when the engine is hot and we're cranking it? We have thought about a leaky injector, but it couldn't be leaking all the time because the system will sit at over 40psi (shut it off and let it sit, fuel pressure climbs as gas heats up) for easily 15 minutes, so doesn't appear to be a problem of an injector leaking all the time but ofcourse an injector could be dumping fuel when it's sposeto spray a nice pattern, we have not pulled any injectors yet. If you let the vehicle sit so it's hot, fuel pressure is over 40psi, then you try to start it (say 20 minutes after you shut it off) the fuel pressure will drop from 40psi to 28psi, then crank some more and finally fall to 21psi. The fact that you have done some cranking at something inbetween 40psi and 21psi (starting at the 40psi though), and it still won't start just doesn't seem right for a fuel issue.

Any thoughts or help would be greatly appreciated. We have verified spark on all plugs, we tried to do this with the coilpacks hot, but hard to know if they were as hot as they should have been to recreate the problem, clean and recleaned the MAF numerous times. We are happy to replace the fuel pump if the 21psi when cranking and 34psi when idling are way off, from the Toyota specs I believe the idling at 34-35psi is not far off, but while cranking the pressure is not that high.

Another wild scenerio we have thought of is the spark being weak, but with starting fluid it's so much more volitile than gas it might ignite with less of a spark? Kinda a shot in the dark, and one coil pack is brand-new, but the other two are original...vehicle is a '96 4Runner with 190K miles from NY (i.e. alot of rust/oxidation, etc)...we are happy to replace the other two coil packs, but have yet to find an obvious reason why we would need to replace them, all have checked out with ohm verifications up to this point (though not sure if my buddy did those with the coil packs hot right out of a non-starting engine). We also pulled all the plugs and coilpacks and had them spark open so we could watch, I would say the new coil pack looked like it had a hotter spark, but the others did spark without any problem, just maybe a bit weaker than the new coilpack.

Again, any help would be greatly appreciated, we're happy to replace parts, but frustrating when you can't figure out what part you should be replacing.

Thanks a bunch!
Mark Brodis
Castle Rock, CO

**bray** · 07-22-2006, 01:51 PM

I'm not sure how much help this will be but I owned an '87 Runner but with a 4 banger that had the same problem. Diagnostics pulled up a bulletin that called the situation 'Hot-Soak'. The mechanic performed a high pressure fuel injection cleaning and all was well.

**99FlowedTaco** · 07-22-2006, 01:54 PM

wrong forum there is a 4runner section here for this damn post

nilson · 07-22-2006, 02:09 PM

Quote:

Originally Posted by 99FlowedTaco

wrong forum there is a 4runner section here for this damn post

someone piss in your cornflakes this morning?

**99FlowedTaco** · 07-22-2006, 02:10 PM

no just tired of all the idiots posting shit in the wrong fucking forum because they dont take the xtra 20 seconds to LOOK and see where their damn post belongs.

Angry Andy · 07-22-2006, 09:32 PM

Quote:

Originally Posted by 99FlowedTaco

no just tired of all the idiots posting shit in the wrong fucking forum because they dont take the xtra 20 seconds to LOOK and see where their damn post belongs.

Thread moved to 4runner tech.

But be easy on the Noobs....you shouldn't call them an idiot until after a hundred or so posts.

99..thanks for linking me to the thread though....

mabrodis · 07-23-2006, 01:28 AM

Quote:

Originally Posted by 99FlowedTaco

no just tired of all the idiots posting shit in the wrong fucking forum because they dont take the xtra 20 seconds to LOOK and see where their damn post belongs.

Hmm, if you had taken the 4 seconds to read the first sentence of the post you would have realized I said I crossposted it (meaning in two forums on this site) and on 2 other Toyota forums. (it was already in the 4runner area also)

I totally agree in keeping Tacoma specific items seperate from 4Runner specifc items...however, this is NOT a 4Runner specific item, it happens to be on a 4runner which has the exact same fuel system as on a like-year Tacoma...there are probably more Tacomas currently being driven, so doing a broad search for help/ideas in places which include Tacoma-specific areas makes perfect sense, atleast to me, since I favor finding results and sharing them with others instead of bitching about the model-plate on the vehicle and where the question is asked.

However, nevertheless, let's get on to the vehicle, today we replace the other 2 coil packs (so all 3 are less than a month old) and no change at all. We probably should replace the fuel pump, but don't have time before leaving for a weeklong 4wheeling trip tomorrow, vehicle runs fine when it runs, so we'll just have to bring plenty of starting fluid, but we'll have other support vehicles, so shouldn't be a big deal.

Thanks for the suggestions, when we finally get to the bottom of this (and really only two things remain, fuel pump and injector cleaning/flow-test, we'll post up a big explaination about what we found which might even be useful for *gasp* Tacoma owners...

All in good fun...

Mark

mabrodis · 07-28-2006, 11:42 PM

For those that care this issue has been resolved, the write-up(s) are here:
http://forum.ih8mud.com/showthread.php?t=102573

Basically it was a bad fuel pump jumper wire (from the tank connector to the actual pump), the wire was burned black, had gotten hot enough the plastic connector fell apart when we took it out, wire looked horrible (and yes this is INSIDE the tank, not a good place for a hot wire)...we spliced in a new wire, soldered connections, used a normal blade style electrical connector on the positive side of the pump (which held on about 10 times as hard as the factory one would), buttoned it all back up, and voila, works perfect...the pump might have been ok, but we replaced that too while in there, but the obvious problem was the wiring, we have the wire to take a pic of (as soon as we find it in the toolbox)...

Now fuel pressure is 42psi ALL the time (like it should be)...

Hope this thread helps someone in the future...

07-22-2006, 10:35 AM	#1
mabrodis Newbie Join Date: Jul 2006 Posts: 5	'96 4Runner delayed hot start problem... Greetings, we are trying to diagnose a problem on a '96 4Runner, 3.4L V6, not a Tacoma I know but we're grasping at straws here trying to find some guidance...crossposted also (and on 2 other Toyota forums, with no magic answers yet)... The engine runs fine normally, occassionally gets a "Fuel Trim too Lean", which (if I'm reading things right) means it's actually running rich and the trim has maxed out whatever leaning it can do...however, the real problem is after running the engine until up to normal temp, then shutting it off, it will start again within about 15 minutes with no problems, but if you wait till after 15 minutes the vehicle will not start, until about an hour later when things have cooled down more apparently. While it's cranking and not starting, it's sputtering and sounds like it's trying to start but just not quite there (sometimes it will even run for a few seconds at about 300rpms then die), firing, backfiring, etc, but never actually gets going. You can, however, start it by spraying starting fluid into the throtle body and it will fire up, makes a horrible pinging noise for a few seconds and then idle normally, however, while it's idling, it's still not all there, if you rev it up it will not rev up normally, will hit about 2500-3000 rpms and just stay there for about 5-10 seconds, apparently (as best I can tell only because it kinda 'feels' like that) because there is no more fuel to rev any higher. After the 5-10 seconds it will rev and drive normally. We installed a fuel pressure guage on the fuel rail so with the hood open we can monitor pressure and while cranking the engine (when it won't start) the pressure shown is 21psi, very consistent. However, when the engine is cold and doing short cranking bursts (so it won't start, just to see what the pressure is when you know it will start if you want it to) the pressure is also 21psi. As soon as the vehicle starts idling the pressure shown climbs to 34-35psi. If you rev the engine you see the pressure drop down to maybe 27-28psi and then climb back up as it calms down. (I say "pressure shown" because the gauge is a new B&M fuel gauge, so should be accurate, but I wouldn't bet my life on it) We replaced the fuel pressure regulator (back side of the fuel rail) last night and that unfortunately didn't fix a thing. We have a fuel pump ready to go in and can put that in. The fuel pressure numbers we were reading from Toyota's documents of normal idling pressure of 32-36 (I believe, going by memory here) and if you disconnect the vacuum line off the fuel pressure regulator it was sposeto go up to about 38-44psi...on this vehicle disconnecting the vacuum line to the regulator did absolutely nothing, didn't change the pressure in the fuel rail at all, and we have never seen fuel pressures in the 38-44psi range at anytime when running. So do those numbers sound right at all to anyone? The problem I see is if the fuel pump can put out 34-35psi, like it's doing while the engine is idling, why isn't it doing that when the engine is hot and we're cranking it? We have thought about a leaky injector, but it couldn't be leaking all the time because the system will sit at over 40psi (shut it off and let it sit, fuel pressure climbs as gas heats up) for easily 15 minutes, so doesn't appear to be a problem of an injector leaking all the time but ofcourse an injector could be dumping fuel when it's sposeto spray a nice pattern, we have not pulled any injectors yet. If you let the vehicle sit so it's hot, fuel pressure is over 40psi, then you try to start it (say 20 minutes after you shut it off) the fuel pressure will drop from 40psi to 28psi, then crank some more and finally fall to 21psi. The fact that you have done some cranking at something inbetween 40psi and 21psi (starting at the 40psi though), and it still won't start just doesn't seem right for a fuel issue. Any thoughts or help would be greatly appreciated. We have verified spark on all plugs, we tried to do this with the coilpacks hot, but hard to know if they were as hot as they should have been to recreate the problem, clean and recleaned the MAF numerous times. We are happy to replace the fuel pump if the 21psi when cranking and 34psi when idling are way off, from the Toyota specs I believe the idling at 34-35psi is not far off, but while cranking the pressure is not that high. Another wild scenerio we have thought of is the spark being weak, but with starting fluid it's so much more volitile than gas it might ignite with less of a spark? Kinda a shot in the dark, and one coil pack is brand-new, but the other two are original...vehicle is a '96 4Runner with 190K miles from NY (i.e. alot of rust/oxidation, etc)...we are happy to replace the other two coil packs, but have yet to find an obvious reason why we would need to replace them, all have checked out with ohm verifications up to this point (though not sure if my buddy did those with the coil packs hot right out of a non-starting engine). We also pulled all the plugs and coilpacks and had them spark open so we could watch, I would say the new coil pack looked like it had a hotter spark, but the others did spark without any problem, just maybe a bit weaker than the new coilpack. Again, any help would be greatly appreciated, we're happy to replace parts, but frustrating when you can't figure out what part you should be replacing. Thanks a bunch! Mark Brodis Castle Rock, CO Last edited by mabrodis; 07-22-2006 at 10:39 AM.

07-22-2006, 01:54 PM	#3
99FlowedTaco Shrockworks 4x4 Products TTORA GOLD Sponsor Join Date: Dec 2004 Location: Houston, Texas Posts: 4,213	wrong forum there is a 4runner section here for this damn post __________________ Mitch 99 Tacoma Reg Cab 4wd 3.5" lift - 35 x 12.50 x 15 BFG KM2s Lifted, locked (F/R) and ready to rock http://www.shrockworks.com Got questions on a product we sell , please PM any questions.

07-22-2006, 02:10 PM	#5
99FlowedTaco Shrockworks 4x4 Products TTORA GOLD Sponsor Join Date: Dec 2004 Location: Houston, Texas Posts: 4,213	no just tired of all the idiots posting shit in the wrong fucking forum because they dont take the xtra 20 seconds to LOOK and see where their damn post belongs. __________________ Mitch 99 Tacoma Reg Cab 4wd 3.5" lift - 35 x 12.50 x 15 BFG KM2s Lifted, locked (F/R) and ready to rock http://www.shrockworks.com Got questions on a product we sell , please PM any questions.

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07-28-2006, 11:42 PM	#8
mabrodis Newbie Join Date: Jul 2006 Posts: 5	For those that care this issue has been resolved, the write-up(s) are here: http://forum.ih8mud.com/showthread.php?t=102573 Basically it was a bad fuel pump jumper wire (from the tank connector to the actual pump), the wire was burned black, had gotten hot enough the plastic connector fell apart when we took it out, wire looked horrible (and yes this is INSIDE the tank, not a good place for a hot wire)...we spliced in a new wire, soldered connections, used a normal blade style electrical connector on the positive side of the pump (which held on about 10 times as hard as the factory one would), buttoned it all back up, and voila, works perfect...the pump might have been ok, but we replaced that too while in there, but the obvious problem was the wiring, we have the wire to take a pic of (as soon as we find it in the toolbox)... Now fuel pressure is 42psi ALL the time (like it should be)... Hope this thread helps someone in the future...