96 4Runner Hard start when engine warm/hot (long/detailed)

I've been having this issue for a couple of months now and haven't had much luck in tracking down the issue. What is happening is that once the engine (96 4Runner V6) has warmed up (isn't overheating or anything) and I shut off the engine, after about 15 minutes or so it is impossible to get it started again without using some starting fluid. If the engine is shut off and I try to start it again within about 5 minutes everything starts up fine, but past the 5 mintues it get harder and harder to start again. Between 5 and 15 minutes I can sometimes get it started if I hit the gas at just the right time, but after that I have to wait for about 50 minutes before I can get it started again.
When I do get it started, either with starting fluid or waiting, it runs perfectly for as long as I want to run it.
I've attached my computer to the OBD and monitored/logged the values that the sensors are spitting out and they seem to be the same as on vehicles that are running with no problems. That includes things like the coolant and intake air temps, O2 sensors and others. I've also checked the resistances on a number of the sensors and have found them to be in the right ranges as specified by the Toyota docs from TIS. I've also cleaned the MAF sensor with a little electronics cleaner. I've changed out the plugs and wires too (not Toyota parts, but the problem was happening before and after this change so figure that isn't it). Also just replaced the fuel filter since it was cheep.
I'm not really sure what sensors are used at startup (open-loop in the computer), but everything that I can test electronics wise seems to be ok. I was wondering if maybe it could be a problem similar to vapor lock? I haven't really been able to test the fuel pressure during the times that it won't start (fuel pressure regulator?) and I haven't been able to have the injectors tested yet.
The real strange thing is that once I get it started it runs without any problems at all. No check engine light or anything. Idles nicely, good power at all speeds, no stumbling.
I did take it to the stealership, but that was a total waste of time as they recommended that I change the plugs/wires (already done) and fix the super small crack in the airbox (not the problem) which I could test out with duct tape. $90 down the drain.
Anyway, any ideas/suggestions would be greatly appreciated. Also, does anyone know what sensors are involved during startup (coolant, intake, egr, etc.)? I get this bad feeling I'm going to have to start replacing parts to get this fixed and I really don't want to have to start replacing injectors and sensors that don't need to be replaced.
Thanks ahead of time for any help! I'd love to get this fixed and post all the steps/fixes since I've seen issues like this posted before and not many have any resolutions.

Welcome erkinne!

It seems you have covered all your bases. But you need to hook up three diag testers, and keep them hooked up.

Inline sealed spark tester. (so it wont arc out)
A fuel pressure tester
And an injector noid.



all of these have to monitored when the condition happens.
some scan tools will allow you to monitor the spark too.

other wise it could be vapor lock.
but in a injected engine? maybe.

Wow.

I can't remember, but is the fuel pump in the tank? It sounds like a fuel starvation problem of some sort?

Isn't there a filter in the tank too?

Good luck bro. If you don't get enough help here try Yotatech and Tacoma Territory also.

WristPin said:

Welcome erkinne!

It seems you have covered all your bases. But you need to hook up three diag testers, and keep them hooked up.

Inline sealed spark tester. (so it wont arc out)
A fuel pressure tester
And an injector noid.



all of these have to monitored when the condition happens.
some scan tools will allow you to monitor the spark too.

other wise it could be vapor lock.
but in a injected engine? maybe.

Click to expand...

WristPin, I haven't looked around for those sorts of test equipment. Is that mainly in the hands of the dealership or can you find that stuff at parts shops? Also, what does the injector "noid" test? Is it an on vehicle test or is the injector removed from the vehicle for this?

calamaridog said:

Wow.

I can't remember, but is the fuel pump in the tank? It sounds like a fuel starvation problem of some sort?

Isn't there a filter in the tank too?

Good luck bro. If you don't get enough help here try Yotatech and Tacoma Territory also.

Click to expand...

calamaridog, the fuel pump is in the tank and the main fuel filter is about under the driver's seat, but there is also the little bag/filter that is on the fuel pump also. We had thought about pulling the fuel pump and buying a new one to test with, but since the engine runs so well at all times other than after having been stopped for the right amount of time we didn't think it would be the best thing to try first. I'm sure it is a fuel delivery issue of some sort, but it is almost certainly heat related which I would figure would almost eliminate the fuel pump since I wouldn't expect it to heat up a bunch in the large amount of fuel it is sitting in. Might try playing around with a new fuel pump though if the tests on the fuel pressure/delivery look strange.

I also posted this to yotatech also, so we'll see if anyone there has some ideas on this.

erkinne said:

WristPin, I haven't looked around for those sorts of test equipment. Is that mainly in the hands of the dealership or can you find that stuff at parts shops? Also, what does the injector "noid" test? Is it an on vehicle test or is the injector removed from the vehicle for this?

Click to expand...

you can get all these tools from Snap-On, or some of the indepenent tool dealers.
a noid tester is simple. basically, you disconnect the injector harness, and plug in the noid. you buy a kit of em, for all different types of vehicles. there is one that will fit.
you plug it in, and when the injector gets volts the noid lights up.
that light is what you look for, for proper injector function.

what i would do, is go to a local shop, talk to a tech. ask him when the tool trucks come by. or get the drivers numbers and call them. any dealer will know exactly what im talking about.

the only thing i am not sure of, on a 96 is the fuel pressure testing procedure.
i know 95 and earlier use a banjo bolt on the fuel line , that you tap into to check pressure. they may or may not be changed in 96.
I assume they are unchanged.
the alternative test fitting used on most american, and new 2000 and up is a schrader valve fitting.
you know the same kind of valve that you inflate tires with.

and i wouldnt go throwing expensive parts at it.
if it is a delivery problem, you need to trace it down. it could be a fuel pump relay.

I have the EXACT same issue with my 92 2.4L 4x4 truck. I cannot figure it out either. The FSM points to a coolant temp sensor as the likely cause. I replaced it and still has the issue. The odd thing, and you might try this, is that when it is difficult to start, all I have to do is shut it down and then recrank and wham, starts like it's cold i.e starts well.

It is like there is no relay of information when the engine is hot so the fuel delivery is either delayed or non existent until I restart i.e. turn off engine computer and restart.

I do not think that fuel pressure is an issue because a cold start would be slow as well. Mysterious and frustrating.

I have read that the fuel pump relay sensor often times has issues BUT that is only on certain model years-mine was not in that grouping.

WristPin said:

and i wouldnt go throwing expensive parts at it.
if it is a delivery problem, you need to trace it down. it could be a fuel pump relay.

Click to expand...

Thanks for that info WristPin, I'll look into that since I wouldn't mind doing the tests myself.

Jukelemon said:

I have the EXACT same issue with my 92 2.4L 4x4 truck. I cannot figure it out either. The FSM points to a coolant temp sensor as the likely cause. I replaced it and still has the issue. The odd thing, and you might try this, is that when it is difficult to start, all I have to do is shut it down and then recrank and wham, starts like it's cold i.e starts well.

It is like there is no relay of information when the engine is hot so the fuel delivery is either delayed or non existent until I restart i.e. turn off engine computer and restart.

I do not think that fuel pressure is an issue because a cold start would be slow as well. Mysterious and frustrating.

I have read that the fuel pump relay sensor often times has issues BUT that is only on certain model years-mine was not in that grouping.

Click to expand...

I had considered the coolant sensor, but I get pretty reliable readings from it when I hook my computer into the OBD II system. Mine actually won't start no matter how often I shut it off though. It is totally dead and to get it going I have to use starter fluid. That will usually get it going, but I have to get it about about 1200 rpms for it to stay running when I use starter fluid. I posted this on Yotatech also and there was a suggestion to clean out the Idle Air Control (IAC) valve on the throttle body since it controls whether or not the engine gets a bit more air on startup and if this is clogged it might keep the engine from getting the correct amount of air at low rpms. I'm going to try cleaning that soon and see if that helps at all.

there is a diagnotic port under the hood. one of the pis is a hot wire when the fuel pump is running. maybe you can tap into this, and monitor the voltage.
i dont know where you can obtain this specific info. possibly the fsm. just a thot.

Well, tried cleaning the IAC valve, but that doesn't appear to be the problem. Guess I'm down to checking fuel pressure and the injectors

erkinne said:

Well, tried cleaning the IAC valve, but that doesn't appear to be the problem. Guess I'm down to checking fuel pressure and the injectors

Click to expand...

do you need any help getting the tools?
i can find some part numbers and where to get the stuff if you want.

WristPin said:

do you need any help getting the tools?
i can find some part numbers and where to get the stuff if you want.

Click to expand...

Any help would be much appreciated. I found the fuel noid on snap-on's website, but the main trouble I'm having at the moment is finding a fuel pressure kit that has the correct banjo bolt to fit the fuel rail. I could do the test other ways I suppose, but if I could find a resonably priced fuel pressure tester that would be a first step.

Thanks!

you can pick up a cheap ass pressure tester at shucks/kragen/checker. ( name depends on the region)
and the followin p/s are snap on's for banjo bolt fittings.

FUEL FILTER INLET FIA420 AND FIA421

FUEL RAIL SUPPLY AND FUEL FILTER OUTLET- FIA310, FIA311, AND FIA312
i havent yet seen the parts, but if you contact a dealer, you can give em these p/n and he will get you what you need.

this is the link for the spark tester. at 15 bucks its a good buy.

http://buy1.snapon.com/catalog/item...&group_ID=1352&store=snapon-store&dir=catalog

Thanks for all the suggestions on this...erkinne is a good friend of mine and we've both been fighting with this problem...he's actually on vacation now so I'm driving his 4runner to attempt to figure it out. I was getting the pieces together for the fuel pressure gauge and a local race shop pointed out this:
http://www.bmracing.com/index.php?id=products&sid=4&cat=17&subcat=&pid=72

It's a off the shelf kit from B&M which is actually for a Civic/Talon, etc but it is exactly what I was looking for, the only question was the thread size/pitch for the banjo bolt...after pulling the 4runner's one out I was relieved it was the same...so I bought that kit from a local race shop ($34 with tax) which includes a new banjo bolt with a 1/8" threaded opening in the head, a 90-degree male/female, and a gauge with a 1/8" threaded male attachment. So basically it was perfect, bolted right in, I trimmed the plastic timing cover a bit to see the gauge (it ends up almost totally under that plastic front cover piece). I drove it around like this, stopping often to look at the gauge, etc...I have since added a 3" riser 1/8" threaded piece and another 90-degree piece, so the gauge is nicely viewable...pretty slick setup, glad the guy at the race shop showed me this.

So, now the details, when the vehicle is sitting there with the key "ON", engine not running, and kicking the engine every so often (I wanted to see what pressure it was getting before actually starting it), I got 22psi consistently, wasn't sure if that was meaningful or not, next I started the engine, let it idle, pressure was 32-33psi, quite stable, if I revved the engine up the pressure would drop to about 28psi and as soon as I let go of the throttle it would hit maybe 34-36psi, if I opened the throttle wide open really quick I could get the pressure reading down to about 26psi probably.

Next I disconnected the vacuum line going to the fuel rail pressure regulator (not sure of the official term, but it's on the backside of the engine)...disconnecting that I believe is sposeto up the pressure on the fuel rail to 38-44psi...I noticed...absolutely nothing, no change what-so-ever, so I started feeling for vacuum, I could feel no vacuum at all on that hose, just putting my finger on the intake where it plugs in, couldn't even feel a hint of vacuum...so that might be meaningful.

Next I drove a few miles got the engine nice and warm, shut it off for 15-30 minutes and looked at the pressure. It's a hot day and after that time the gauge was reading 38psi (highest I had seen it at all), I went to start the engine (knew it wouldn't start) and it didn't, I cranked it once and looked at the gauge, it was at 27psi, I cranked it several times more and looked each time, now at 26psi.

I sprayed starting fluid into the throttle body (via a vacuum hose in the side, this has been our trick to start it for the past several months while it's had this problem), engine fires up, and is idling right at 30psi, I rev it up and can get the pressure to drop to about 24psi and when I let off the throttle it will hit about 34psi (a much wider swing than the revving I was doing while at home, also possibly something to note, while driving this, immediately after starting it with starting fluid the engine will be idling along fine, but it's not all there, if you floor it just sitting there at times it will only hit about 3000 rpms and just sit there, apparently no more gas so can't rev up higher, about about 10-15 seconds it's all there and revs and drives fine...interesting because it seems something has to repressurize or something like that, just because it's running doesn't mean it's all there)...

I drove home, stopped at home and let it idle, looked at the gauge, it was bouncing wildly between about 24psi and 34psi, and it was consistently bouncing, almost like a pattern, if I revved it up the gauge stabilized at about 30psi (I think), but as soon as it went back to an idle it was back doing it's wild bouncing. I was thinking maybe this could be because a injector is flowing more than it should when it's on, but that's just a shot in the dark.

So, with those numbers does that ring any bells for anyone? The thing that struck me was ALL the numbers are low I believe, and the fact that having the pressure regulator vacuum lines connected/disconnected made zero difference at all, I don't believe that's right, so some suspicious lies there, however, then I was thinking what if all the fuel pump can push out is that pressure, so the pressure regulator is basically doing all it can but the pressure from the tank is low maybe? Anyone know of a easy way to test the pressure on just the pump? I guess I could try to rig up something at the fuel filter to tap off pressure...

Any ideas/thoughts would be appreciated...

Not sure if Eric mention this in the original post but the vehicle has 189K miles on it...maybe with that mileage range it would help someone to think of something it could be..

Thanks,
Mark

Pics of the gauge setup...

Are you just going to leave it in?

2ndGenToyotaFan said:

Are you just going to leave it in?

Click to expand...

Not indefinitely, but until this is resolved I'm sure we will...according to the shop I bought it at the gauge is fine for underhood temps and all that, so could leave it there I'm sure if we wanted, but don't plan on it.

Really need to get an idea of what the specified ranges should be. But let's put that aside.

Here is what we know. When it is cold, and you pressure is 22psi, the engine will start, idle etc. When it has been run, and then rested, pressure is 28 psi and will not start. It seems illogical to think that fuel pressure is an issue.

I have thought, in relation to my issue, that it is an issue with my cold start injectors in that the relay does not recognize a certain temp range, and as such, does not utilize the cold start injectors-which in your case might explain why you must use starting fluid.

I go back to thinking it has to be relay related/signal quality related not pressure becasue of how well it starts cold-like mine.

Have you cleaned out your throttle body yet-I mean really clean with a toothbrush and carb cleaner? Have you checked your Coolant Temp sensor?