abalagtas

I'm getting a weird problem.

My truck will start/run fine and then it will intermittently have a problem starting. Basically, the idle will be really rough and trying to give it gas will cause it to stall....sometimes it will stall right away and not hold an idle....sometimes it will idle rough and then smooth out and be fine. When it's running rough there is black soot in the exhaust. When the truck doesn't start, I smell fuel.

I changed the plugs yesterday. They had typical soot on them....so coolant isn't leaking into the cylinders. No sign of coolant in the oil. Cleaned the TB a few weeks ago. Oil is new and so is coolant.

Here is sequence:

1 - start truck - no problems - let it warm up - shut/start 3x no problems
2 - start truck - no problems - let it warm up - shut engine. wait few minutes and restart - rough idle, but smooths out
3 - start truck but rough idle won't hold try 4x, won't start
4 - start truck - rough idle, but smooths out

No real rhyme or reason. It will start cold and not start warm and visa-versa.

NO CEL codes


This is on '91 4Runner V6

abalagtas

ugh...think it's the HG. Just started the truck and there seems to be more white smoke then normal.

abalagtas

So....used to 'block tester' from napa to check for exhaust in the cooling system....nothting....don't see any coolant in oil.....drove truck around....no signs of the problem....wtf...it fixed itself?....glad truck is running well, but hate not knowing what the problem was since I could possible get stuck.

joel1952

When it doesn't run, does it have fuel and spark?

abalagtas

Joel....yeah...it's getting fuel and spark.....my mech is leaning towards AFM, but it doesn't thro any codes. They have only reproduced the problem 1x, but it cleared. Here is sample of the what happens.

I drove truck to mech about 5mi mix of frwy and street. No problems starting or during the drive. As soon as I parked the truck, it stalled. I immediately tried to restart and it would not start. I was dropping off the truck before shop opened so I filled out envelope to put key in. B4 dropping off key I gave is a start one more time...and it fired up and idled no problem.

The next day the mech tried to reproduce the problem, but couldn't right away. Later in the morning, they finally reproduced the problem - rough idle black smoke....but it cleared up and they haven't been able to reproduce again.

There are no codes

joel1952

I have a similar problem with a 94 T100. No codes, either. Is yours FI or CARB? Mine is Fuel injected

I suspect a bad fuel pump, so I am hooking up a pressure gauge. I hope to see the pressure drop (when it sputters or dies or won't start) FYI, I believe it sputters for 10 seconds at idle before it dies because of residual fuel pressure.

A low pressure reading would mean either the pump is not pumping well or the pump electrical circuit has an intermittent short.

I also have no code, but that doesn't indicate much on an OBD1 car like yours or an early OBD2 like mine (or anything about fuel pumps and electrical shorts).

Test the air flow meter by unplugging it when the the truck will not start. It will start if that is the problem.

LET US KNOW WHAT HAPPENS

abalagtas

Well, the shop couldn't reproduce the problem again. They even had a mech drive it home. no problems. So they gave it back no charge.

I drove it home taking a mix of side streets and frwy. No problems.

The next day I drove to pick up my kid from school <2mi. It stalled at 2nd stop light. Turned on my hazards and waited for light to change...I was making lft turn so wait was longer then usual. When light turned green I started car...after a couple of seconds of stumbling...it started no problem. I pulled in to corner gas station to make sure it was ok...np. drove to school/back home no problems. When it stall it runs 'rich', you can smell the gas and the exhaust is black.

This morning I started up np. I let it idle for 30min occasionally reving to 2.5k...np. I stopped and immediately tried to restart....will not start...like trying to start a flooded carb engine.

No codes....I changed the o2 sensor it was covered in a think layer of soot...I think a symptom not the cause....truck still didn't start. It's been about 1.5hrs I'm going to give it a try again.

How do you isolate a problem when it's intermittent?

offroadnutz

Intermittent problems are hard to track down. Usually you have to wait till it breaks completely or start throwing parts at it. I had a friend that had a similar problem on a different engine and something was causing the cold start injector to operate intermittently and flood the engine. I dont remember what it was but one thing you might try is unplugging the cold start injector after you start the engine, and then drive the truck around and see if it still does it. If the problem goes away then you know its related to the cold start injection system. Could also be a temperature sending unit going bad and causing the computer to send more fuel.

joel1952

Alfred,
NOW THAT IT'S NOT RUNNING, THAT"S GOOD because now you check for spark and fuel while it is not running.
I would do the fuel test first.


Fuel

1) Do the fuel pump jumper to see if the pump is running.
http://www.4crawler.com/4x4/CheapTri...CheckConnector
PICTURE D shows the jumper location
You should hear it running.
If it does not run, that is a pump circuit problem (an electrical problem OR a bad pump)

If the pump runs...

TRY TO START IT (hopefully it still will not start)

2) Check for fuel flow and pressure. Hook up a fuel pressure gauge. Check for proper pressure and fuel flow. If you don't have a gauge, do the following

I am not sure on your truck. There should be a fuel return line. Do you know where it is? Do you have a manual? Disconnect the line and check flow with a watch and cup. Flow should be maybe a cup in less than 10 seconds. I don't know for sure, but if it takes a minute to fill a cup, that would be inadequate

Check for pressure with your thumb over the end of the hose. The pressure should be about 80PSI I think, so if you can lightly press you thumb on the end and stop the flow, that is INADEQUATE pressure. It should take FIRM thumb pressure, maybe 5-10 pounds of thumb force to stop the flow.

TRY TO START IT
Hopefully it still will not start
THAT WOULD MEAN THAT YOUR FUEL PUMP IS BAD

SPARK
Hook up a spark plug to a spark plug wire and ground the plug on the engine. You should have a bluish/yellow spark, every couple seconds.

Hopefully you have a good spark.
TRY TO START IT
Hopefully it will not start
Now you have confirmed that you have a bad fuel pump

GOOD LUCK

offroadnutz

Joel1952 How can a bad fuel pump cause excess black smoke? That is evidence of to much fuel or fuel not getting burned? Just curious....

joel1952

Good question.

If the pump has low fuel pressure or low fuel flow,
OR the pump is intermittent on/off/on/off every 1-3 seconds...

...the mixture in the cylinder is too lean to ignite properly, so unburned or partially burned fuel comes out of the tailpipe.

i.e. There is fuel, but not enough to burn properly, so you see smoke and smell fuel

My 94 T100 has similar symptoms. I bought a $12 fuel pump a Harbor Freight Tools a couple weeks ago, but have been too busy with the new girl friend to install it. I'm trying to impress her with the porsche anyway. Then when she is hooked, I will start driving her around in my truck. ;-)

abalagtas

ugh...after not starting all afternoon...went out for dinner and came back and it started np and idle fine.

Joel, when it wasn't running I did the fuel pump check...shorting Fp B+ and the pump was running....I don't have a fuel pressure gauge tho...gonna have to try an borrow one.

Metalhead1

My brother in laws 90 3.0 was doing the same thing so I pulled off the fuel return line on top of manifold and no fuel was coming out so I suspected the fuel pump. The pump ran with it jumpered so just because it is running doesn't mean it is good. We replaced the pump and it ran fine.

Shady Cadence

Replace, don't check, but replace the ground connector for the two brown wires under the dash above the driver's kickplate. Do yourself, or ask your mechanic what he'd charge you to do it. Takes maybe 15 minutes.

Most intermittent problems are the result of poor electrical contact, and a weak ground connection can affect everything slightly, not enough to throw codes, but enough to make...

WEIRD ISSUES.

try it.

joel1952

YEAH!!! I should have told you to pull the hose off at the same time as you jumpered the fuel pump to check for flow....

You could also check for pressure with your thumb.

But then the damn thing started running again.

I made the same mistake myself, last time mine quit running. I can't drive it now because of the unreliability. It runs ok for weeks, albeit only a few hundred miles, between dying.

I suppose the solution is to let it idle in the driveway all day. No reason not to. I think the pump runs constantly at one speed, so the pump would probably quit running within a few minutes to a few hours whether it is on the road or in the driveway....???

abalagtas

FIXED!

I was able to reliably reproduce the problem for my mech. Basically, let it idle for 40min reving up to 2.5k periodically.

After a couple of days, they suspected the water temp sensor. They said they could hook up diagnostics to the computer and test it first since the sensor was behind the engine near the fire wall.

They replaced it and it's been running fine. Cost me $325. $200 was diagnostics $125 parts/labor.

Hope this will help someone in the future with weird symptoms!

joel1952

Good luck. I hope that fixes the problem.

My question, "Did your fuel pressure get checedk when the problem occurred?", to rule out the fuel pump??

abalagtas

Hi Joel,

I don't think so. I'm going to do some follow up checks because I'm sure things are fouled from all the excess gas that's been dumped in the cylinders.. ie plugs o2 sensor. I'll run fuel pressure check too.

joel1952

Hi,
It's been a month. Has it run right all the last month? Have you put plenty of miles on it to determine if it's a reliable ride again??

abalagtas

Hey Joel,

I haven't had the time to check the fuel pressure, but the truck has been running strong.

.....however, I do notice my gas milage has gone down a bit....I used to get about 120mi at the half tank mark, but now I'm at 100-110mi.....I pulled the EFI fuse, but it didn't change.