Need help for 3.1 engine

[Darkover]

Hi to everyone,

I hope that I did not write it a second time because something was lost when I wrote this first.

I have a 1990 3.1 with a little problem.

The car works fine. There is no engine light, and there is no error code when
I read the ECU.

But sometimes it happens that the engine will not start, or start very hard
when I stop it with hot engine only for a few minutes. If this happens, I have to push
accelerator pedal to maximum and it will start.
This happens once a week or perhaps every two weeks.

And is need to much gas. 15-16l/100km.

I replaced spark plugs, air filter and examine many other things (vacuum hose, TBI, spark-wires, distributor).

It will help me very much if someone can send me a logfile of WinALDL to his engine to compare everything. (olaf@criseis.ruhr.de)

Olaf

[86TATpi]

How long has it been doing this? It could be flooding itself, possibly a leaking injector or a sensor on it's way out hasn't tripped a SES light yet. If you can, check the fuel pressure. You can also see if the injectors are possibly dripping a little when the car is shut off.

[Darkover]

> How long has it been doing this?

Hm..2 month minimum, because I bought the car two months ago.

> It could be flooding itself, possibly a leaking injector or a sensor on it's
> way out hasn't tripped a SES light yet.

This is what I am thinking, too. And it is a reason why I am interested in a Logfile from a other car.

>If you can, check the fuel pressure.

This is on my check-list. :-)

> You can also see if the injectors are possibly dripping a little when the car
> is shut off.

I checked this. I have not seen any dripping, but the problem is the problem did not happen so often. I also opened the TBI and the injector as far as possible and found no problem.
And there is another point. I understand that this is a common problem with other car, for example with 3.8 engine. But on car with a TBI? If an injector will dripp, he do it on a closed throttle. I did not expect that this is a big problem and I think the fuel pressure for TBI is much less compare with other kind if injection.
But when I now think about it, how can the engine start normaly without pushing accelerator pedal? I think the answer is, it is only possible with IAC-Valve wide open. Perhaps I have to examine this valve very carefully.

But I think this problem is not so important. I can repair it when it happens once a day, because it is easier to find than. More important is to find the reason for the huge gas consumption because of the high gas prices in Germany. (If the reason for both problem not the same)

Olaf

[86TATpi]

I can't remember for sure but I think the fuel pressure is only 15 or so. Port Injection is a minimum of 35 on some (newer ones it's up in the 40s). You shouldn't have to hold the pedal down to start a fuel injected car. Injectors should pulse fuel in. Pull the IAC out, check for carbon build up where the pintle seats and on the valve itself. You can pull that whole spring and pintle out for cleaning. Just be sure to push it in enough before installing it or you may damage it. Does the car have one or two injectors? I know a 5.0 tbi has one for each bank and the 2.2 tbi has just one. How hot is it running?

[Darkover]

> I can't remember for sure but I think the fuel pressure is only 15 or so.

I did not remember it, too. But this is not a problem because I have the Heynes manual for TransSport and can read it there.

> You shouldn't have to hold the pedal down to start a fuel injected car.

I know this. And on normal starts I have not to do. This is only a solution for the cases when it did not start well.

> Pull the IAC out, check for carbon build up where the pintle seats and
> on the valve itself.

I will do this tomorow when there is no rain. .-)

> Does the car have one or two injectors?

There are two of them, one for each part of the engine.

http://www.ruhr.de/home/criseis/injector.jpg

If you like, you can view them. :-]
I examined them and think they are good.

> How hot is it running?

I think everything runs fine. The only reason why I gave this engine a
closer look is the high consume of gas and that I was curious about american engines. To tell the truth, I have never seen or own a car that is so old and looks so good.

By the way: Idle-speed of engine without A/C is 645-700upm measured with WinALDL.

Olaf

[86TATpi]

I would say that engine on average should get low mid 20 miles per gallon. Sorry, don't know what the conversion would be. Check the oxygen sensor also. When they get older that aren't as active. They produce their own current and the more active it is the better the car will meter fuel. When they get older they aren't as active. Sometimes they don't trip codes. I can get the dealer specs on what the sensors should read. But I can't get them until Monday.

[Darkover]

> I would say that engine on average should get low mid 20 miles
> per gallon.

I got 15 miles per gallon! And I drive very slowly and carefully.

> Check the oxygen sensor also.

I think it looks not so bad. This mean it is working, but I read that
they become more slowly when they getting older. But I think my one
is okay.

Today I clean IAC Valve and EGR valve. EGR looks not so bad, but IAC needed some cleaning. I know that it is easy to destroy IAC when
push it back to the TBI, but I was carefully and did not destroy it.

Than I had the idea to check ignition timing. I was 10 degree to late! That is strange.
I turn it to 0 degree with ignition shift wire pull to ground. Two things are happen. At first the engine sounds much better. At second idle speed goes up. Before it was 650upm reported by WinALDL, Heynes said 550 to 650 is okay, now it is 750upm.
When I now drive the car it drives much more powerful, I thing 20 horses more than before. I would say the engine runs good now, but it is hard to understand that the idle speed is to high, because I expect that the ECU will push it lower.
When I switch on AC the idle goes from 750 to 850, but I think this is okay. I think I will drive the car now for two weeks and look how much gas it will need.

Olaf

[Darkover]

I few minute ago I also check vacuum at intake manifold (I hope my english is good enought). It is now 18 inches or 480mm. My, very old,
measurement device for vacuum said this is okay.
I also checked all hoses/wires for vacuum.


When I start cold engine, the idle speed is much to high, aroung 1200rpm. I know it should be higher at cold engine, but I think this is to much.

Olaf

[86TATpi]

15-22 inches is normal. Computer controlled cars shouldn't need anything done for timing. They are controlled by the computer. Idle can be adjusted, but there is a procedure since basically that IAC is what is responsible for remembering that's where you want it.

[NiteOwl]

Mmm.. 86TATpi, the 3.1 has a distributor. You can turn it to change the base timing. In fact on the 3.1 it is recommended to check the base timing at 100,000 km.

The PCM controls the advance added to this base timing by signalling the ignition module in the distributor. But if your base timing is off, the PCM can't correct for this.

Olaf,
Mine is a '94 3.1.

At cold start it will idle at up to 1200-1400 rpm on the tach. It will gradually settle to below 1000 rpm within a minute or two. At normal operating temp no A/C 550- 650 rpm idle, with A/C around 750 rpm.

From the U body manual idle speeds are (normal operating temp) 900 max park or neutral, 650 +/- 50 drive, 800 +/- 50 A/C on drive. PCM commanded idle varies with temperature.


The 3.1 Engine idle speed is a function of total air flow into the engine. IAC valve position + crankcase valve flow + throttle valve opening + calibrated vaccum loss through accessories.

The throttle body has a sealed set screw to hold the throttle plate open for a factory calibrated air flow. This results in the IAC being positioned a CALIBRATED number of steps (counts) from the seat.

DO NOT try to ADJUST the IDLE USING this SETSCREW!!! Misadjustment can result in IAC or throttle body damage!

If the PCM commanded idle and actual idle are significantly different and your sure of the IAC, you may have a small vacuum leak. Idle speed is programmed into the PCM, no adjustments.

I seem to remember city fuel consumption being rated at 13l/100km city, less than 10l/100km highway, have to check.

[Darkover]

> Mmm.. 86TATpi, the 3.1 has a distributor. You can turn it to change the
> base timing.

This is right. But it is interesting to think about why they made this changeable, because the ECU takes it signal from an electronic sensor that never moves. So it should be no reason to change it.
And another good question is why it changed on my car. At this moment I think someone with bad skills (the last owner) in repairing detect the high idle time and change the timing to get it lower because of the emission control in Germany. I don't think it is possible to pass this check with to much idle.
Hm..but with wrong timing it should not possible also. That is funny because I bought the car two months ago with a fresh emission control check.


> At cold start it will idle at up to 1200-1400 rpm on the tach. It will
> gradually settle to below 1000 rpm within a minute or two. At normal
> operating temp no A/C 550- 650 rpm idle, with A/C around 750 rpm.

Using tach I see 1500rpm at cold start and 900 without A/C. But the tach is lieing compare to WinALDL. And my ears say the idle speed is not so bad. Which one I can trust more? :-)
I think the interesting point is the consumption of gas. It will need two weeks and than I know more.

> From the U body manual idle speeds are (normal operating temp) 900
> max park or neutral, 650 +/- 50 drive, 800 +/- 50 A/C on drive. PCM
> commanded idle varies with temperature.

What is 'U body manual'? My Heynes said minimum idle speed 550-650. But it said nothing about maximum idle speed.

I measure my 750rpm in park. On drive it is 650. I thought the reason for this is that the transmission brakes the engine a little bit and that this is not good. But to tell the truth, I have many experience with cars, but nothing with automatic-transmission. They are a little bit unusual in the country of 'autobahn' and so it is my first car with it.

So perhaps everythink is okay now and only Heynes is wrong?

> The 3.1 Engine idle speed is a function of total air flow into the engine.
> IAC valve position + crankcase valve flow + throttle valve opening +
> calibrated vaccum loss through accessories.

I know this and I was thinking, perhaps there exist a little problem with IAC. I removed IAC and cleaned it and it needed much cleaning. I also cleaned the hole for IAC. Than I push back the needle of IAC like Heynes told me before I install it again.
By the way: I am an engineer for electronic and so I was very curious about how IAC-valve is working. But I did not find out now. I think it is a very funny kind of valve. Perhaps I should buy a new one and open the old one only for curiosity. :-)


> DO NOT try to ADJUST the IDLE USING this SETSCREW!!! Misadjustment
> can result in IAC or throttle body damage!

Of course, but perhaps I should check if the seal is in order. Perhaps someone else did a bad job there.


> If the PCM commanded idle and actual idle are significantly
> different and your sure of the IAC, you may have a small vacuum
> leak. Idle speed is programmed into the PCM, no adjustments.

This was my first thought, too. But I checked it. Unfortunatly there are many MANY places for a possible vacuum leak on this car.

> I seem to remember city fuel consumption being rated at 13l/100km
> city, less than 10l/100km highway, have to check.

Yes, but my one needed 15l, sometimes 16l in city. And on highway it needed 14.8-15l, too. And I only drove 130-140km/h.

Olaf

[86TATpi]

IAC is a stepper motor. It works kind of like a power door lock motor. It moves in and out based on throttle position. A scan tool may say the IAC is, for example, 74 steps. The tool to test them is kind of cool because you have full controll over how much it moves to test it for idle.

[NiteOwl]

ECU gets rpm and crank position signal from the ignition module IN the distrubutor. Move the distrbutor and you move the sensor in a relative way to the crankshaft. Timing chains do stretch (or jump a tooth), gears wear. People play with things.

U body is the GM vehicule group designation for the trans sport, silhouette, and lumina vans. To really know your van get the GM shop manual. Check out www.Helminc.com.
Heynes are good manuals but lack the detail of the OEM manual that you need to troubleshoot problems. Everything is explained to almost an engineering level.

So you do have normal idle speeds in park and drive 750/650 rpm.

Automatic transmissions load the engine because the "clutch" is the torque converter.
The "input" of the converter always spins at engine rpm and pushes on the transmission fluid, pumping it away. The output, attached to the transmission, is a turbine that is turned by the fluid pumped out. The turbine is not spinning when you are stopped (0 rpm, but torque is multiplied 2x or more). The fluid between the two however is being pumped and the energy used results in that all too familiar engine loading when going from P or N into gear

Hows your voltage? The PCM will increase idle RPM if the battery voltage is low.

As for your MPG (or l/100km) see what happens. Around here 120km/h is about as fast as you can go. Posted limit is 100km/h.

Going through the U body manual poor fuel economy causes;
Tire pressure
Fuel leak
A/c on all the time
Heavy loads
acceleration too much, too often
Brake drag
TCC (torque converter clutch) operation, see below
exhaust system restriction
Induction system and/or crankcase air leaks
Knock sensor incorrect retard
Initial timing
Thermostat always open or incorrect heat range
Compression.

The TCC is controlled by a valve that is known to fail due to debris blocking it open. The TCC eliminates the slip of a torque converter when the transmission is in third gear, improving fuel economy. Easy to check, fairly easy to fix. Bad TCC, higher l/100km....

[Darkover]

> ECU gets rpm and crank position signal from the ignition module IN
> the distrubutor.

I have seen this module. :-)

> Move the distrbutor and you move the sensor in a relative way to the
> crankshaft. Timing chains do stretch (or jump a tooth), gears wear.

I know they stretch an my engine has 200000km but not 10 degree.

> People play with things.

That is right. And I think I know the reason now. The problem now with correct timing, when I start the cold engine the idle speed is to high. (1200-1400) when I change transmission to drive it will jump a little. I think this is not good for transmission. So I have to wait one minute when idle becomes lower before I can drive.
I think this is the reason why someone change the timing to make the idle speed lower because he did not find the true reason for the high idle speed.

> Heynes are good manuals but lack the detail of the OEM manual that
> you need to troubleshoot problems. Everything is explained to almost
> an engineering level.

That is interesting because I thought the Heynes is VERY good. I have never seen a book for DIY people who show how to hone a cylinder.

The only problem with heynes, Some day I will dream about the sentence: "On models equipped with Delco Loc II audio andi-theft system, be sure the feature is disabled..." because they wrote it three times on every page.
Hm..and perhaps it is strange to use a pocket calculator for repairing a car to calculate feet,quarts,miles,ounces and gallon to something more comon for me. :-)

> So you do have normal idle speeds in park and drive 750/650 rpm.

But I have 750rpm only when I wait one minute.

> Automatic transmissions load the engine because the "clutch" is the
> torque converter.

I understand this because one of the reason I bought this car, I was interested in automatic transmission and I read as much as possible about this kind of transmissions.

But there is one thing I did not understand. I know what TCC is and the reason for it.
When I drive my car (3T40 transmission) it uses at first the three gears, and than the TCC goes on. Before I know about TCC, I thought this was a fourth gear.
Why is TCC only working in the third gear? Will it not save gas when it goes on in the other gears too?

> Hows your voltage? The PCM will increase idle RPM if the battery
> voltage is low.

That are interesting news, I did not know.

WinALDL said 12.3Volt at idle speed and 13.8-14.1V when driving. I did not check with my DMM until now.

> Tire pressure

I checked, was okay.

> Fuel leak

Of course not. I enjoy the view of the car from below when I grease the bearing near the tire. The car looks like new from below.

> A/c on all the time

Hey, boy. Its Germany. I wear a big sweater now and it is 9degree Celsius (using calculator) or 48.2F when I look out of my window. I only use the button with 'HEAT' written on.

> Heavy loads

Only a small belly.

> acceleration too much, too often

I swear I drive like my own grandfather!

> Brake drag

I don't think so, and I replaced brake lining when I bought the car. Everythink looks good.

> TCC (torque converter clutch) operation, see below

I can feel that it is working. When I drive like my grandfather after some time at 2500rpm the revolution goes down to 1800rpm at 60-70km (calculator) 43miles. (Normal speed inside of town)

> exhaust system restriction

I have a (many) logfile of WinADL and can see how O2 sensor is working.
Perhaps you are curious about some datasheet?

http://www.ruhr.de/home/criseis/page1.gif
http://www.ruhr.de/home/criseis/page2.gif
http://www.ruhr.de/home/criseis/page3.gif
http://www.ruhr.de/home/criseis/page4.gif
http://www.ruhr.de/home/criseis/page5.gif

They are all done with ignition timing corrected to OTC. (0degree)

> Induction system and/or crankcase air leaks

This is what I believe now. A little air leaks I did not found. Perhaps around heating system or automatic speed control. (sorry I did not know the correct english word)

> Knock sensor incorrect retard

I dont think so. My belly said it is good. :-)

> Initial timing

Yeah! I hope this was the reason!

> Thermostat always open or incorrect heat range

Now, you can view it on the picture.

> Compression.

I hope now. But I can not measure it because my compression checker is to short and to big for this engine with the small spark plugs.

> The TCC is controlled by a valve that is known to fail due to debris
> blocking it open.

This was my first idea ever, but I can feel how it is working.

Olaf

[LMP]

Originally Posted by Darkover

>
there is one thing I did not understand. I know what TCC is and the reason for it.
When I drive my car (3T40 transmission) it uses at first the three gears, and than the TCC goes on. Before I know about TCC, I thought this was a fourth gear.
Why is TCC only working in the third gear? Will it not save gas when it goes on in the other gears too?

This clutch is very small and very limited in torque capability. It can only withstand cruise power and it gets out of the way (reverts to torque converter) as soon as you request more power.

So, since 1st and 2nd gears are normally used for acceleration , thus high torque loads, it would not support that anyway. On 4 speed transmission (with 3.8) , it also kicks in in 3rd.