flooding at start, missing at idle

[71/454]

I have posted a little about this before and have tried a few things but this thing is going to drive me to drinking, well more anyway. I have a 94 k1500 4l60e extended cab 295000 kms. I bought it as an insurance write off so I have no idea what has and has not been done.
My problem is when it's started first thing in the morning, and it's more pronounced when the outside temp is colder, it fires right up runs for about 30 seconds misfires a couple of times and then it seems as though it goes on to flood itself. Not bad enough to stall it just bad enough to make it sound like a lumpy cam. This is where it starts to get weird. When it warms up a little about when the gauge starts to move and it is off the high idle it idles perfect. But when it gets to operating temperature it seems to miss so bad that it really shakes the truck. You don't hear it so much in the exhaust but it sometimes changes the idle speed on a hard couple of misses. If you rev it slowly it will miss til about 1500 rpm then smooth out. No ses light, the only one I got was for the o2 and I have since changed that. I have thought about the iac but the idle moves where it should when it should. I do not have the tool to check the fuel pressure, but if it can flood itself seems like it's ok, right?

Things that have been done to the truck so far, I can see the po has done the intake gaskets and it has a new rad and trans, not that that really matters. I have changed the plugs, wires, cap, rotor, pcv, fuel filter, o2 sensor and egr.I have given it seafoam thru the tbi and gas tank. I found that the base timing was set at 2 degrees after tdc, so I changed that to 2 dgrees bdtc and the miss seems much worse now, so I'll put that back to 0. I have gone around the tbi with carb cleaner to check for leaks at the base, the throttle linkage is tight, replaced any suspect vacum lines. The only thing I know is wrong is that the clutch fan is sticking and making the engine run about 70 degrees celcius, I have an electric I am going to put in, but the fan would not cause all this right? All help is very appreciated because I am at my wits end. Dave

[ChevyTech]

Do you have an ohm meter for testing the coolant temp sensor?
If you do I can post specifications.

The next thing I would check for is a worn distributor.
On these distributors the housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues.

[71/454]

Thanks for your reply chevytech. Yes I do have an ohm meter, please post the specs. Also I do have another known good distributor and new module that I have left over from when I was fooling with my brother in law's truck, perhaps I will swap that. Dave

[ChevyTech]

To test the coolant sensor, unplug the wire connector and test the resistance across the two terminals of the SENSOR with an ohm meter.

The sensor screws into the intake manifold, on the front passenger side, by the thermostat housing.

Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.

[71/454]

Ok, I was thinking I should test it at cold and compare it to the outside temp, and then warm the truck up to operating temp shut it off and test it and compare against the gauge. If I pull the plug off the sensor while it's running the idle dips and I get a SES light. Does the diagnostic method sound right?

[ChevyTech]

Letting it sit overnight and testing it cold is a good idea, and is where I would expect a problem, by the drivability problem your truck is having. Then test it at operating temp.

Unplugging the coolant sensor with the engine running will set a trouble code.

[71/454]

Ok I let it sit overnight and tested it and I will test it later today after I drive, if I get a new meter. I have two meters and the first one stopped working, maybe it was the cold, I did it outside. And the second the test lead broke off. I'm not sure if the meter is wrong or if it had something to do with the test lead, but it did show an even 0 when they were touched. The resistance between the two pins at ice cold is 9.6, yeah thats what i said too. So if the meter is right the coolant temp sensor is bad, making it too lean, making it miss, and thats why the plugs are white. I will get a new meter and test it hot and maybe cold again to make sure, and I will let you guys know what I find out. Thanks for the help Chevytech, you are an awful big help on this board and I really do appreciate it. Dave

[71/454]

Ok got a new meter and tried it when it was hot. Previously I have only used a meter to check voltage, polarity, and basic continuity so I'm unsure here. I shut the truck off and checked it, it went off the chart at 200 ohms so I switched it to 20k, I assume this is 20000 ohms and I got a reading of .25 thru .28 bouncing back and forth between these two. I'm now assuming this is 250 ohms thru 280 ohms. Looking at this and rereading my previous post I think the sender is ok because I don't remember what I had the meter set to this morning, but now I'm guessing 20k. That would mean the reading this morning was 9600ohms. Am I doing this correctly, like I say I am not sure I am using the meter correctly, the decimal point really throws me a curve.

[Blue_71]

if im not mistaken, i think on the 20K scale .25 or .28 would be 2500 to 2800, making your ECT sensor read that your truck is at 82*F when your truck is actually at 210ish*F

at 210*F (operating temp), you should be able to take a reading while on the 200 ohm scale

on the 20K ohm scale, you take your reading and multiple by 10,000. 10,000X.25= 2500

on the 2K ohm scale, you multiple your reading by 1000

[ChevyTech]

I have several different meters and some are not as easy to determine how much to multiple the reading by.

Sometimes I measure a resistor, that I know the ohms value of, to see what I need to multiply by.

To me, reading my old analog meters were much clearer.

Blue_71’s math looks good but I do have a meter that is unclear and would match your calculation also.

[71/454]

Ok I tested it again this morning and after it was hot.
Morning. cold on 20k 8.07 it was 3 degrees celsius out. according to the chart thats about right if the meter and the math is accurate.
Afternoon. hot 193 on the 200 scale. this is what makes me think the math is correct because the chart shows this as about correct operating temp. My gauge in the truck only shows about 80'C maybe it's out a bit, but I bought a new autometer to set up my electric fan I installed so I will confirm that later. So I think the temp sensor is fine.
I was sitting in the truck this morning waiting for it to open the t stat so I could double check my electric fan coming on and after having to sit there the whole time I think it now misses all the way thru the temp range, and it seems to be alot worse now too at operating temp.
Last night I let it run in the dark to double check the plug wires, nothing. I put the timing light on all the wires down by the plugs and watched the light flash to see if there was any electrical miss, nothing.
I double checked the timing, and this is where it got a bit weird, it runs different when you disconnect the timing wire everybody knows this, not rough just different, at least mine does, but it didn't seem to miss as much. The timing was fine and the lines lined up and didn't move. I decided to reconnect the timing wire and watch the timing mark. It was off the scale by about an inch, but i could still see it, and it moved quite a bit towards the advanced side and it's movements definitely coincided with the missfire. After spending so much time watching the engine heat up and cool down with the fan install it sure does seem to change it's behaviour all of a sudden, it will shake and shudder, then smooth out for a bit sometimes the idle will change. Long and short, I'm going to pull the distributor tonight and put in the other one I have, it has been rebuilt at some point and I know it works. This missing seems to be getting worse and I'm afraid I'll get stuck on the side of the road one of these days. Thanks for the help guys, I'll keep you posted, and keep the suggestions coming. Dave

[ChevyTech]

When you changed the spark plugs did one look significantly different then the rest of the plugs?

It would be a good idea to do a compression test on all cylinders to make sure it is not a mechanical problem causing the misfire.

[71/454]

When I changed the spark plugs originally they were all sort of usual black with some nasty crust on them, but none seemed darker or worse than another. I pulled all the plugs again a little while back before I started all this and they were all white, that made me think there was something making it lean.
Chevytech I agree with you, I will do a compression test before I do anything else to make sure, start with the basics, right?
Yesterday I realised I had another, I'm not sure what its called but it holds the injectors and fuel pressure regulator, so I put my injectors in and tried the fpr and no difference.
The highlight is that I got my electric fan install done and I think I have the fan coming on just right now.
It's funny, if it is a burnt valve it wouldn't bother me so much because I know it's not gonna leave me on the side of the road. The rest of the truck is darn near mint, so it's worth putting a rebuild in, but I don't want to do that and have the new motor miss as well.
Thanks Chevytech and you guys for all your help and suggestions I will post what I find.

[71/454]

Well I thought I should update this, but I don't have anything other than it is still doing it and I have confirmed it is intermittent. It has been really cold here lately so I have been plugging the truck in. When it starts not plugged in it chugs, plugged in fires right up and runs clean and after a little bit it starts to miss. If I tip into the throttle bust barely I hear a heavy vacuum sound almost like a wheezing. I had a look at all the vacuum lines again and they seem to be good. The one thing I did notice is that the clip that holds the electrical plug to the IAC is broken. That tells me someone's been in there before, and i think there is a special way it screws in (something about jumpering a and b pins together) so maybe they didn't do it right.

[ChevyTech]

Question:
When the engine does start, does the engine have a fast idle that slows down as it runs? The IAC (idle air control) is what gives the fast idle speed when started cold.

After the engine is shut off, and before it is started, the IAC should open somewhat. When the engine is cranked, and if the IAC does not open at all the engine will usually “load up” or “flood.


The IAC (Idle Air Control) controls the air passing through a throttle pate bypass passage.

The IAC (and computer) control the idle speed.
The IAC (and computer) is what gives the engine a “fast idle” speed when started cold.
The IAC also supplies more air to compensate for the extra load when the A/C is on. If you have A/C and turn it on while listening carefully you should be able to here the IAC controlling the idle as the A/C clutch engages and disengages.

IAC passages can get plugged up with carbon or muck. The IAC units get erratic as they get old and stick. Use care when cleaning the IAC. The IAC should not be cleaned with carburetor cleaner or other harsh chemicals. If the chemicals get down inside the IAC, it will damage it.

Jumping the terminals you referred to is for getting the system to relearn the idle without driving it to reach the criteria the for the system to do it on its own.

[71/454]

Thanks for your reply Chevytech,

It does have a fast idle when started cold, but it does seem to come down real quick, thats when the chugging starts.
If you tip into the throttle slowly and very slightly you definitely hear it gasp, like it is going lean.
I got a check engine light the other day when it was idling like chitty chitty bang bang, so I will check the code to see what it says, hopefully it will be of some help.
Two questions if you don't mind,
1 I was thinking about just trying another tb unit from a junkyard truck, good idea?
2 Could you tell me the recomended way to replace an iac in the event it is the problem, I have been told to go about it several different ways. Is it necessary to jumper the pins to make it relearn, or is driving it enough?

[71/454]

Sorry with regards to my comment about tipping into the throttle, I should have added "when warmed up to operating temp".

[Bob B.]

There should be a couple of ground wires under the thermostat housing bolts. Are they there?

[ChevyTech]

I was thinking about just trying another tb unit from a junkyard truck, good idea?

Make sure you use on off an engine with the same cubic inches. The model 220 TBI is use on many engines and different size injectors are used in the TBI depending the cubic inches of the engine it is on.

Could you tell me the recomended way to replace an iac in the event it is the problem, I have been told to go about it several different ways. Is it necessary to jumper the pins to make it relearn, or is driving it enough?

If the pintle (plunger) is extended while off the TBI unit and it is not retracted before reinstalling IAC will get damaged if the “pintle” (plunger) bottoms out in the TBI when you screw the IAC back in.

The tip of the pintle must not extend more than 28mm which is 1.10 inches from the shoulder toward the electrical connector from the threads.

If the IAC is working ok the ECM/PCM should relearn the IAC position. Specific driving conditions must be met before the ECM will relearn the IAC position. Driving the vehicle should bring the IAC to the correct position.

Jumping the terminals you referred to is for getting the system to relearn the idle without driving it to reach the criteria the for the system to do it on its own.

Being you said it did have a fast idle when started, and then it slowed down, it sounds like the IAC is working.

To me it sounds like your vehicle has a problem you have not found yet.

You could try disconnecting and plugging the hose to the EGR valve and taking it for a test drive.

Take a look in your distributor.
On these distributors the housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues.

[71/454]

Thanks Chevytech. The EGR is a new GM one, and the distributor has been changed. I had the code read I saw the screen, but didn't see a number, all it said was oxygen sensor, lean, any I idea what to make of that? The O2 sensor is new within two months, when I replaced it the first time it was the original gm, and the code was o2 sensor failure and it could not be reset, so I replaced it. I haven't checked the plugs in a while, but last I did they were white.

[ChevyTech]

Originally Posted by 71/454

I have posted a little about this before and have tried a few things but this thing is going to drive me to drinking, well more anyway. I have a 94 k1500 4l60e extended cab 295000 kms. I bought it as an insurance write off so I have no idea what has and has not been done.
My problem is when it's started first thing in the morning, and it's more pronounced when the outside temp is colder, it fires right up runs for about 30 seconds misfires a couple of times and then it seems as though it goes on to flood itself. Not bad enough to stall it just bad enough to make it sound like a lumpy cam. …

Originally Posted by 71/454

…. I had the code read I saw the screen, but didn't see a number, all it said was oxygen sensor, lean, any I idea what to make of that? The O2 sensor is new within two months, when I replaced it the first time it was the original gm, and the code was o2 sensor failure and it could not be reset, so I replaced it. I haven't checked the plugs in a while, but last I did they were white.

Being we are not sure if it is rich or lean, it is best to trust the ECM code at this point.

It most likely had a code 44. If you get the specific codes it will help me know how to help you better.

An exhaust leak in front of, or close behind the O2 sensor can cause a false lean code.

If the engine is misfiring it can give false ECM indications.

Even if the EGR is new you should try disconnecting and plugging the hose to the EGR valve and taking it for a test drive. Just because the valve is new does not mean the solenoid and the rest of the system is working correctly.


I suggest testing the fuel pressure.


Here is some info about fuel pressure testing I saved from a previous reply I made to a similar post. Hope the links still work.

C/K truck TBI systems do not have a fuel pressure test port.

The fuel pressure is tested by using fittings to “T” in a pressure gauge. I like to T in the pressure gauge where the fuel filter is located. If the pressure is good, both the pump and regulator are ok. If the pressure is low it could be the pump or the regulator. If the test is done with a method that allows the fuel filter to be in place, a dirty filter can also cause low pressure. The regulator is inside the TBI unit. Stopping the flow in the return line momentarily will test to see if a low pressure problem is caused by the regulator. A bad regulator can let the fuel return to the tank instead of maintaining the correct pressure. If pinching off the return line, using care not to damage the return line hose, makes a low pressure reading surge above the specification pressure, then the regulator is the problem.

The TBI fuel pressure specification for small block Chevy’s is 9 – 13 PSI with the truck running.


Here are some web sites showing fuel pressure test equipment. The first tool gets installed where the fuel filter goes. Most people use the tool in the third site next to the TBI unit.


I you already have a pressure gauge like shown in the second web site below, all you need is the tool shown on the first web site. If not, the third would get the pressure tested for the least money.

http://www.sjdiscounttools.com/ta37650.html

http://www.actron.com/product_detail.php?pid=16174

http://www.actron.com/product_detail.php?pid=16175

http://www.cfm-tech.com/catalog/fuel...er_2940807.htm

Another addition to the list:
http://www.tradervar.com/cgi-bin/sto...;page=3641.htm

[71/454]

I would agree with you on the fuel pressure test, but as yet have not been able to find anyone I know with a tbi one, lots without the tbi adapter. So it looks like I'm going to have to buy one.

[71/454]

Ok, I finally got my fuel pressure tester in the mail. I bought an actron one, like the one chevytech suggested. The good news is the fuel pressure sits a hair below 12psi all the time when running. After I shut it off the fuel pressure drops down to 10 then to five and then 2 and then almost nothing. It takes 20 maybe 30 seconds to bleed off. I'm guessing this is ok? I know that 12psi is good, and the fact that the fuel pressure does not drop like a stone after the motor is turned off is good also. I would not expect it to hold 12 psi all day. Please correct me if I'm wrong. So the bad news is, I haven't found my problem. I now have a tbi from the wreckers than I'm going to try.

[ChevyTech]

Being it can maintain 12 PSI while running I don’t think it is causing the problem you are having but when you shut it of it should not be dropping the pressure as fast as it is. This is a common condition caused by aftermarket fuel pumps letting the fuel drain backwards through the pump as soon as it is shut off.

At this point I really don’t have an opinion of what is wrong with your truck.

Originally Posted by ChevyTech

Even if the EGR is new you should try disconnecting and plugging the hose to the EGR valve and taking it for a test drive. Just because the valve is new does not mean the solenoid and the rest of the system is working correctly.

If you have not tried this yet, it is an easy test and it take no special tools. Sometimes the EGR solenoids let vacuum through the solenoid when it should not.

Another common problem on these trucks is the distributors housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues.

[71/454]

I did try plugging the line to the EGR a while back and driving it, all it did was give me a check engine light. As far as the distributor I checked the bushings in the old one and it seemed good, but just to be sure I have replaced it with one that I know is good, module and pickup coil too. At this point I'm stumped. I am going to change out the tbi when I get time.
The funny part is I really believed the fuel pressure was going to come up low. Reason being because of this problem, and because whenever I pull a trailer I get a check engine light and the code says O2 lean. I guess the key is to not sweat the small stuff. But I'd rather be working on the twin turbo in my 72 right now.