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 (on a 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.

Eric K.

 

Have you tried cleaning the IAC valve? It is located under the TB. I was having the same problem as you, and after the clean everything has been fine.

 

I haven't actually cleaned it, but I will give that a try. Did you bother with replacing the gaskets on the throttle body and on the IAC valve? I would imagine they would be fine even though the TIS documents say they should be replaced. Thanks for the suggestion 2000t4r!

 

No I have not replaced any gaskets, though I did check the condition and they were fine.

 

I have a very similar if not so severe issue on my 98.

I will have a look at the IAC tonight

David

 

This problem sounds like a common problem experienced by airplane pilots when the fuel injected engines were introduced from Lycoming. Essentially, after an engine had warmed up and was shut off, the fuel along the fuel rail would essentailly boil off and it would be very hard to start it afterwards. I dont have all the technical jargon surrounding the issue but that is a simple explanation. The engines would restart fine after they cooled off.

I would start with a simpler diagnosis such as what was suggested by 2000t4r before I went poking around with the fuel pumps or FI system.

Just my .02

 

I don't believe its vapor lock but I guess anything is possible.

David

 

Well, it doesn't seem to be the IAC. I just pulled it off, cleaned it out and then went out for a drive. After waiting 25 minutes I went back out and the problem remained. Looks like I might be down to checking out the injectors and fuel pressure in the rails when I'm having the problem.

 

Have you considered replacing the fuel filter? How many miles? 3.4?

 

Already did, but didn't see any change. It has almost 190k on it.

 

Anything new on this? I don't have as bad a situation as the first guy but if I drive the truck and park it for a few minutes (say Blockbuster), it cranks and starts but dies a few seconds later. I turn off the a/c or lower the radio and crank her up again w/ a little gas and I'm fine.

I'm worried that it will turn to this type of issue. I have a red top (but I haven't checked voltage) but I'm pretty sure I'm fine. I've had the red top for about four or five months and this only started recently.

Any thoughts? Fuel filter and other recommendations have been done within the last six to eight months. I'm definitely into preventative maintenance and upgrading while at it.

 

main relay?

does it seem like it only happens during the hot season?

ive seen main relay from hondas that failed over the yrs and symptom similar to this.

 

I'm dropping in a post here that my buddy made on ih8mud. We are still dealing with this problem, but at least we now have an idea of what the pressures and stuff are in the fuel system. My buddy's post follows....
--------------

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...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


__________________
'85 Mini, 2nd owner...add-ons: 31" MTRs, oil & dirt stains...
'00 Echo, 1.5L of FURY!

 

Some pics of the guage setup can be found here. It is temporary until we get this fixed up, but we'll just leave it in the engine bay until we have figured out what is wrong.

http://www.erickinne.com/gauge.htm

 

Mark, you did a great job at least tapping into the pressures on the fuel rail so we can help you diagnose this thing for you. Those pressures do sound a bit low, but there may be more than one factor at work here causing your no start condition.

The 3.4L should measure 38-45 psi and the typical stock regulated pressure at the rails should be around 42-43 psi stable at all RPMs (it may drop lower at idle when there is a vacuum pulling on the regulator diaphragm). The fact that when you crank the motor the pressure drops could be either the regulator or the pump (but sounds like the regulator to me....it may not be bad though, read below). Also watch the fuel pressure drop (have someone else crank over the motor so you can view) when cold (ie when it starts) vs when hot (ie when it doesn't start) and compare. How do they look? Any differences? If your friend will let you view the fuel rail pressures on his as well then you'll get a good idea of what "normal" looks like vs what your seeing with yours (which is well over half the battle).

The way to check the FPR is to use a pair of hose pliers (they are flat on the inside of the jaws and won't hurt the hose when you squeeze down on it) to clamp off the fuel return to the tank and watch the pressure on your guage (you may have to replace the clamp on the hose with a worm clamp since the stock spring clamp may let loose under the higher pressure you're creating). Another issue is the fact you said the vacuum line had no vacuum on it. That is definately an issue when the vehicle is idling, check for a cracked line, blockage or leak in an adjacent line like the brake booster line, etc. You can buy a simple vacuum guage to hook it up to the line and verify exactly how much vacuum is present (should be about 9-12 psi at idle or about 18-24 in/Hg). It would be great to verify a reading of vacuum at the FPR diaphragm on your friends 4runner as well if possible to compare with. You may actually have a vacuum leak causing a tough start condition when warm (since the engine will richen the mixture to start a cold motor).

This link should help you with diagnosis as well:
http://www.deserted1.com/FSM/Repair_...fuepum/ovi.pdf

Do keep us updated because I am very curious what the issue finally ends up being for you.

 

Here are the sender pics for reference by others:

 

Just as a short update, after the fuel pressure gauge didn't turn up any conclusive leaks or very abnormal pressures, we checked out the grounding points in the engine and cleaned those up and made sure they where all good, replaced the spark plugs since the one that where in there for only about 10K or so where pretty nasty and ran some Seafoam through the engine 3 times. Nothing changed. We decided to test out the engine coolant temperature sensor a bit more since I had only estimated the engine temp the first time I did it. We went to pull it out after draining some of the coolant, but when I pulled it out of the socket the top plastic part was broken. Don't think this happened in the socket so that is a bit strange. I have just bought a new one and will be replacing it tonight. Who knows, maybe it was a problem after all. Will update after this has been done.

We where also a bit curious about what fuel pressures will be in the fuel rail on startup and while running. We where never able to get the fuel pressure to change when removing the vacuum line on the fuel pressure regulator which we thought was a little strange. We even put a vacuum on the regulator and it still didn't go down which we thought should happen. Initially the fuel pump with get the fuel pressure up to 21psi when the engine is cranked and when running the pressure will be between about 32 and 40psi. This sounded about right to us.

 

if it was the temp sensor, then ur story w/ using a start-up-fluid doesnt add up.

at a cool engine but hot weather, can it turn over?

 

Ya, not really a problem with hot ambient temps, just with engine bay and engine temps. We didn't think it was the ECT, but wanted to be sure. It broke easily getting it out so had to replace it anyway. Not having that sensor in makes the engine really hard to start. It will run fine when started, but just hard to start. I guess not having it in there could have just made the problem worse and present at cool and hot engine temps

 

Well, the issue has been resolved. Turned out to be a bad wire connection on the fuel pump probably due to a pump that was slowly going bad. For more details head over to this link since I can't post all the info from it here...

http://forum.ih8mud.com/showthread.php?t=99905

Thanks for the help!