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

[mabrodis]

Originally Posted by WristPin

on thos first page here, there is 2 threads that have different problems. all trace back to bad grounds.
toyotas get all pissy when ther ground strap is loose.

Cool...thanks for pulling that up!

Do you know where the grounds are on the engine/wiring-harness? I'm sure we can just look for them, but if we knew what ones were typical problem ones it'd be nice to start there.

My guess is the problem is something like this, a grounding problem, totally unrelated to fuel at all...but after all we've done, atleast it has a clean fuel system...

[erkinne]

Originally Posted by mabrodis

Cool...thanks for pulling that up!

Do you know where the grounds are on the engine/wiring-harness? I'm sure we can just look for them, but if we knew what ones were typical problem ones it'd be nice to start there.

My guess is the problem is something like this, a grounding problem, totally unrelated to fuel at all...but after all we've done, atleast it has a clean fuel system...

Think I found the TIS doc with all the ground points so we will check that tonight in addition to everything else.

[WristPin]

i dont know off the top of my head where they at on a v6.
i dont own a v6, so i cant go snap a pic. sorry charlie.

[WristPin]

and sorry i didnt get a chance to look at tsbs. the floating mgr was there, and he was riding my ass, and plus we were busy.
i usta have an account with alldatata.com they have TONS of repair info.

[mabrodis]

Update...

Tonight we pulled all the ground connections from around the engine, there are only 3 (passenger-side top of fender, driver's side of intake manifold and driver's side inner fender next to battery)...cleaned those off (didn't look too bad), used a dremel with a wire brush to get any oxidation off them, put them all back on...then pulled the coolant sensor (to test it in a pot of boiling water), and it more or less fell apart in our hands (which was interesting because it was working, we measured normal coolant temperatures previously with the ODBII reader, 199 degrees, etc), it apparently was broken at some previous time, we put it in water but even with it sitting on the counter couldn't get anything but a open on it, so apparently a wire or so was broken inside...so that will get replaced. However, interesting enough we put the broken one back in, just as a plug, and went to start it and it wouldn't start at all, we remembered we had opened the fuel rails, so it'd take a bit to fill all up again, but it took a long time, fuel pressure was sitting at 20psi it was sputtering and coughing, backfiring horribly, finally it crept up rpm-wise (fuel pressure went with it, or the fuel pressure crept up and the rpms went with it, couldn't tell), and then it idled perfectly, fuel pressure sitting at 34psi...

Connected a computer and the ODBII thingy said coolant was at -40F, must be some default value when it has no sensor to read...however (this was odd), the coolant guage on the dash still worked, it was at the bottom (cold) when the engine was cold, we let it run and it creeped up into normal range...this is all with the temp sensor on the top of the engine disconnected. So apparently that interior sensor reads something else? Anybody know what it reads? (we were not expected that guage to work at all)

So the fact that it had an awful time starting is suspect, but the computer also though the engine was at -40F, so maybe dumping in alot more gas or something, not sure what would happen with that, but that sensor is getting replaced obviously asap.

Even though the fuel seemed not-so-suspect before, I'm still not sold on that, when we were cranking away it was sitting right at 20psi, then as it was starting to start (coughing, backfiring, etc, for 5-10 seconds) the pressure was slowly creeping up and then at about 26-28psi it started running just fine. To me that was suspicous because if the pump/regulator/whatever could produce 34psi (like it was doing as soon as it got running, or started running as soon as it got there, however you look at it), then why wasn't it at that pressure while we were cranking it? I can not think of a rational reason why the pressure would be less while cranking than it would be while idling (are the injectors putting in more fuel while cranking than idling? Since it is trying to start a stopped engine, which usually takes a hefty boost of fuel I believe...but just guessing)

So all in all we did nothing useful to solve this problem...sigh..

[erkinne]

Found that there is actually another coolant temp sensor that is separate from the EFI sensor that runs the gauge in the dash. The ECT sensor makes a difference in starting the vehicle since it was a pain in the ass this morning to get started. Should have that replaced tonight. Also contemplating the EFI relay and the Circuit opening relay which are both in front of the fuel pump. Not sure how I'm going to test those, but guess it is something else to look at. Still need to pick up one of those noids to check the fuel injectors.

[Jukelemon]

Couple of things:

1- I have a coolant sensor that works. I replaced mine thinking it was the casue BUT it was not. So, do a part number comparison and see if the 22re's are the same. Mine is from a 92.

2- I do not think the gauge in the vehicle is connected to the coolant sensor-pretty sure it is not so that really tells us nothing other than the engine temp is going up and the T stat is working.

3- I still not think it is pressure related because it was fine at cranking last go around. As well, I ran my truck without a sensor i.e. sensor unhooked for a good 100 miles. No change and no issues. I am told that when a sensor dies, the ECU will default to a std map that insures driveability NOT starting i.e. it is made as a safety map to get home/shop/whatever. Now this is for a 22re, who knows what effect it will have on a v6 when removed in terms of starting. Also, the fuel pressure might be controlled by the ECU depending upon the ECU's coolant reading. Not sure though.

The temp sensor is not that expensive in the event that mine does not match up to the v6.

[Jukelemon]

Just saw your posting. What sensors are now in question. The coolant temp sensor should be right under/near the throttle body. Where is this other sensor you are talking about?

[erkinne]

Originally Posted by Jukelemon

Just saw your posting. What sensors are now in question. The coolant temp sensor should be right under/near the throttle body. Where is this other sensor you are talking about?

The ECT (for EFI) sensor is 100% broke so no question about replacing that. Picking that up at the stealership this afternoon and will probably put it in shortly afterword. The other sensor was just for the gauge in the dash which is working fine and I actually don't care much about.

[erkinne]

Interesting, the '92 22RE coolant temp sensor looks to be the same as in the '96 3.4L V6

[WristPin]

to test the fuel pump action, you can open the air box, and push your finger up in the inlet, and push the flapper. once that opens, the fuel pump circut is closed, and should turn on.
with the igniton on, of course.

[AzBearFan]

Originally Posted by Jukelemon

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.

I had this problem with my 22re, found this on Roger Brown's site and straightened it right out... its a way to bypass the fuel pump contact in the AFM

http://www.4crawler.com/4x4/CheapTri...shtml#FuelPump

[Jukelemon]

Excellent reference. SHOULD BE IN THE FACT SECTION!!! Thanks. That might actually help me BUT will not with this issue in the post because he reads psi's during cranking.

Thanks

[mabrodis]

Great tips guys!! As far as having zero fuel pressure that's not the problem. Now we are down to the chance that the 21psi we see when cranking the engine is enough to start the engine when cold, but not start it when warm, I guess it's theoretically possible it's harder to start the engine when warm, or a warm injector really needs more pressure than that, however, why does the pressure go up when it starts via starting fluid? (maybe with the inrush of air the maf finally realizes it and tells the fuel pump to run more?)

What we're doing in the next day or so is to use my oscilloscope to look at the voltage waveforms on all the coilpacks and on the injectors (atleast those we can easily get to the connectors) we'll see what we find there, maybe one or more coilpacks aren't getting a full 12v ever, or maybe when hot they aren't (when wires heatup their resistence goes up, meaning voltage at the end of a wire would go down, depending on how much current if flowing.

So, we'll see and if nothing more, we'll get to use some semi-fancy lab equpiment in the garage...

[yooper]

If this was a 3FE, I would blame a failing fuel pressure regulator and fuel pump check valve. On that engine, when the FPR fails it causes high fuel pressures, especially at shutdown with a warm engine. There is a little plastic ball check valve on the output of the fuel pump that gets jammed closed and gets stuck that way, so the engine is starved for fuel on startup. If you let it sit and cool, as the fuel lines cool the pressure goes down and the check valve gets sucked open again, and all is well. Replacing the fuel pump solves the problem. Replacing the FPR prevents it from recurring. But this is on the 3FE. Just an idea, maybe not applicable. I'm thinking your low pressures might be due to a partially stuck check valve on the pump.

You can read about my experience and how I solved the problem here: http://forum.ih8mud.com/60-series-wagons/6464-3fe-fuel-supply-problem-i-fixed.html

Good luck!

[mabrodis]

Issue has been resolved (so when people find this via a search they don't find a abandoned thread with no solution)...

Look here: http://forum.ih8mud.com/79-95-toyota-truck-tech/102573-fuel-rail-pressure-when-starting-real-time-help-please.html

[pwc69]

I will try and give you a few new suggestions to give you more homework. I have been having intermittent difficulties with my 94 T100 3.0L V6 for some time now and having poured over many repair manuals, specs, and websites looking for the culprit I think I may be able to help you look for the problem in different areas you may or may not have looked at just yet.

It doesn't seem that you have any problem with the fuel pressure, but I find your testing rather interesting. I have the specs for the pressures in the different states here somewhere for the 3.0L V6. I have some other links that I will add if I can find them as I am typing this.

I think the first thing I would try is to pull the EFI fuse (Possibly different for your vehicle) under the hood for 15 seconds to reset the ECU (you will lose all codes stored in there so check it first). Then just see if it starts. It could be the coolant temperature sensor, the oil temperature sender sending or not sending proper information.

Toyota's in general do not like poor grounds. There are an unlimited number of possible problems that can be related to poor grounding somewhere on the vehicle. I recommend going below and reading about the Automatic Downloading of Toyota Service Manuals to get your hands on the wiring schematics and starting ciruit for your vehicle. Find all the harness and engine grounding points and make sure they are intact.

Ignition switches can cause a number of problems if they are worn out by giving varying amounts of voltage at different times. Possibly not allowing all the systems to function properly. This can be hard to diagnose. One way to evaluate the general charging system voltage is to buy a digital charging system monitor that plugs into the cigarette lighter and shows voltage on ACC / On and after starting as the vehicle is running. You can add more systems to see if you are getting unusual spikes or draws anywhere or if you are getting different readings on different drives. This is only a basic guage of the charging system. Before the first starting the a good battery is 12 V to 12.9 V. During Charging it should be 13.5 V to 14.5 V. You should see feel an increase in idle speed when the A/C is on and the voltage drops at a stop light. If it does not then there could be a problem in the charging system, sensor, or ECU. You can buy the tester for $15 at Walmart or Autozone. One way to clearly see if the ignition switch is the problem is to install a bump switch or remote starter to completely bypass the ignition system. Just put the key in the on position and push the button on the bump switch and the starter should kick in with full battery voltage. These run about $15 at most parts stores or Sears.

If you disconnect your Circuit Opening Relay (near ECU on my vehicle) then remove your gas cap and then turn over the engine you will depressurize the fuel lines. If you can't get to or find the Circuit Opening Relay then you can just disconnect the wiring directly to the Fuel Pump, but you will have to go fishing under the vehicle to do that. Just reconnect the relay and gas cap and if pressure was your problem then it should start during or after this process.

The first thing that struck me as I was reading your problem was that you have been spraying starter fluid into the throttlebody. The Throttle Possition Sensor is very sensitive and can be ruined by this. If you remove the hose to the Throttle Body you can see a small hole near the bottom. That is where the Throttle Position Sensor gets its readings. Starter or Carb cleaner in that hole can damage the sensor. Done often enough, can also ruin the O2 sensors. Which would, assuming the ECU is working properly, not allow the ECU to properly judge exactly the proper amount of fuel to send to the injector (including your cold start injector which should normally get extra fuel at each startup unless it is clogged or not functioning). The cold start injector is easy enough to check resistance following the repair manual. Check out the link below for more information on Throttle Position Sensor.

A long shot considering you replaced the coil is a weak spark or improper timing. You can get an inline spark tester for under $10 at Autozone or the like. It has a light that flashes with each spark and you just move it from spark plug to spark plug between starts. My Toyota has to have the DLC1 jumped in order to properly adjust the timing. Also the ECU is taking a reading of several other sensors as the vehicle is starting and while it is running adjusting the Fuel/Air ratio and spark timing for each cylinder. Other sensors to check could be Knock Sensor and Crank Position Sensor.

A poor or bad connection with the starter solenoid (intermittent clicking while trying to start) can cause reverse polarity or arcing potentially sending excessive power to sensors, relays, or the ECU. The likely problems in this circuit are the Circuit Opening Relay, the Fuel Pump Relay, Starter Relay, ECU, and EFI fuse, IGN fuse. There are several other items that could be affected, but these are the front runners. I would consider the ECU as one of the most likely suspects. Considering the expense of replacing this unit, if at all possible, borrow one from someone with the same vehicle just to test the possibility of this being the culprit. Testing the ECU is very difficult and time consuming. Your vehicle can drive mostly fine with a bad ECU under many circumstances. The one thing that seems very strange is that you don't seem to mention any Malfunction Indicator Light coming on or any codes from the ECU. Check out the link for the Solenoid Saver Diode below (under start links).

The best thread I found that may help you out is one from NaterGator for an automatic download of Toyota Service Manuals. You can get all of the manuals on your computer and get all the specs you could ever wish for. The link is below under Manuals and Training.

Another long shot could be vapor lock. I haven't heard of it in these vehicles and would be unlikely in pressurized systems. That could explain the time needed to cool down. Is there any possibility that any fuel line or intake manifold could be close enough to a heat source to get hot enough for this to happen? See links under Fuel System for detailed information on injector system and complete testing.

ECU Diagnosis and Repair links: http://www.enginecontrolunits.com/index.html
http://www.autocomputersupply.com/in...on=Custom&ID=5

Starter Soleniod Diagnosis and Repair Links:
http://www.4crawler.com/4x4/CheapTricks/Starter.shtml
http://www.sherco-auto.com/contacts.htm
http://www.fostertruck.com/sol-saverdiode.htm
http://www.fostertruck.com/dodge/starter%20faq.htm

Throttle Position Sensor diagnosis and repair links:
http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

Service Manuals and Training:
http://forum.ih8mud.com/80-series-tech/128021-fully-automatic-factory-service-manual-fsm-downloading.html
http://www.techinfo.toyota.com
http://www.autoshop101.com/


Fuel Systems links:
http://www.autoshop101.com/forms/h22.pdf

Let me know if you trace the problem or have any questions I may or may not be able to answer. Good Luck!!! Paul pwc@cox.net

[mabrodis]

Originally Posted by mabrodis

Issue has been resolved (so when people find this via a search they don't find a abandoned thread with no solution)...

Look here: http://forum.ih8mud.com/showthread.php?t=102573

Originally Posted by pwc69

I will try and give you a few new suggestions to give you more homework. I have been having intermittent difficulties with my 94 T100 3.0L V6 for some time now and having poured over many repair manuals, specs, and websites looking for the culprit I think I may be able to help you look for the problem in different areas you may or may not have looked at just yet.

It doesn't seem that you have any problem with the fuel pressure, but I find your testing rather interesting. I have the specs for the pressures in the different states here somewhere for the 3.0L V6. I have some other links that I will add if I can find them as I am typing this.

I think the first thing I would try is to pull the EFI fuse (Possibly different for your vehicle) under the hood for 15 seconds to reset the ECU (you will lose all codes stored in there so check it first). Then just see if it starts. It could be the coolant temperature sensor, the oil temperature sender sending or not sending proper information.

Toyota's in general do not like poor grounds. There are an unlimited number of possible problems that can be related to poor grounding somewhere on the vehicle. I recommend going below and reading about the Automatic Downloading of Toyota Service Manuals to get your hands on the wiring schematics and starting ciruit for your vehicle. Find all the harness and engine grounding points and make sure they are intact.

Ignition switches can cause a number of problems if they are worn out by giving varying amounts of voltage at different times. Possibly not allowing all the systems to function properly. This can be hard to diagnose. One way to evaluate the general charging system voltage is to buy a digital charging system monitor that plugs into the cigarette lighter and shows voltage on ACC / On and after starting as the vehicle is running. You can add more systems to see if you are getting unusual spikes or draws anywhere or if you are getting different readings on different drives. This is only a basic guage of the charging system. Before the first starting the a good battery is 12 V to 12.9 V. During Charging it should be 13.5 V to 14.5 V. You should see feel an increase in idle speed when the A/C is on and the voltage drops at a stop light. If it does not then there could be a problem in the charging system, sensor, or ECU. You can buy the tester for $15 at Walmart or Autozone. One way to clearly see if the ignition switch is the problem is to install a bump switch or remote starter to completely bypass the ignition system. Just put the key in the on position and push the button on the bump switch and the starter should kick in with full battery voltage. These run about $15 at most parts stores or Sears.

If you disconnect your Circuit Opening Relay (near ECU on my vehicle) then remove your gas cap and then turn over the engine you will depressurize the fuel lines. If you can't get to or find the Circuit Opening Relay then you can just disconnect the wiring directly to the Fuel Pump, but you will have to go fishing under the vehicle to do that. Just reconnect the relay and gas cap and if pressure was your problem then it should start during or after this process.

The first thing that struck me as I was reading your problem was that you have been spraying starter fluid into the throttlebody. The Throttle Possition Sensor is very sensitive and can be ruined by this. If you remove the hose to the Throttle Body you can see a small hole near the bottom. That is where the Throttle Position Sensor gets its readings. Starter or Carb cleaner in that hole can damage the sensor. Done often enough, can also ruin the O2 sensors. Which would, assuming the ECU is working properly, not allow the ECU to properly judge exactly the proper amount of fuel to send to the injector (including your cold start injector which should normally get extra fuel at each startup unless it is clogged or not functioning). The cold start injector is easy enough to check resistance following the repair manual. Check out the link below for more information on Throttle Position Sensor.

A long shot considering you replaced the coil is a weak spark or improper timing. You can get an inline spark tester for under $10 at Autozone or the like. It has a light that flashes with each spark and you just move it from spark plug to spark plug between starts. My Toyota has to have the DLC1 jumped in order to properly adjust the timing. Also the ECU is taking a reading of several other sensors as the vehicle is starting and while it is running adjusting the Fuel/Air ratio and spark timing for each cylinder. Other sensors to check could be Knock Sensor and Crank Position Sensor.

A poor or bad connection with the starter solenoid (intermittent clicking while trying to start) can cause reverse polarity or arcing potentially sending excessive power to sensors, relays, or the ECU. The likely problems in this circuit are the Circuit Opening Relay, the Fuel Pump Relay, Starter Relay, ECU, and EFI fuse, IGN fuse. There are several other items that could be affected, but these are the front runners. I would consider the ECU as one of the most likely suspects. Considering the expense of replacing this unit, if at all possible, borrow one from someone with the same vehicle just to test the possibility of this being the culprit. Testing the ECU is very difficult and time consuming. Your vehicle can drive mostly fine with a bad ECU under many circumstances. The one thing that seems very strange is that you don't seem to mention any Malfunction Indicator Light coming on or any codes from the ECU. Check out the link for the Solenoid Saver Diode below (under start links).

The best thread I found that may help you out is one from NaterGator for an automatic download of Toyota Service Manuals. You can get all of the manuals on your computer and get all the specs you could ever wish for. The link is below under Manuals and Training.

Another long shot could be vapor lock. I haven't heard of it in these vehicles and would be unlikely in pressurized systems. That could explain the time needed to cool down. Is there any possibility that any fuel line or intake manifold could be close enough to a heat source to get hot enough for this to happen? See links under Fuel System for detailed information on injector system and complete testing.

ECU Diagnosis and Repair links: http://www.enginecontrolunits.com/index.html
http://www.autocomputersupply.com/in...on=Custom&ID=5

Starter Soleniod Diagnosis and Repair Links:
http://www.4crawler.com/4x4/CheapTricks/Starter.shtml
http://www.sherco-auto.com/contacts.htm
http://www.fostertruck.com/sol-saverdiode.htm
http://www.fostertruck.com/dodge/starter%20faq.htm

Throttle Position Sensor diagnosis and repair links:
http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

Service Manuals and Training:
http://forum.ih8mud.com/showthread.php?t=128021
http://www.techinfo.toyota.com
http://www.autoshop101.com/


Fuel Systems links:
http://www.autoshop101.com/forms/h22.pdf

Let me know if you trace the problem or have any questions I may or may not be able to answer. Good Luck!!! Paul pwc@cox.net

The issue has already been resolved (post directly before your's) In this case it was the fuel pump...great info and thanks for posting the links.