Got a new truck with a few issues

[Ackattack]

I picked up a 1990 K3500 with a TBI 454 today. It runs OK, but not right. On the 90 mile trip home I got 7.4 mpg and had the check engine light go on and off while driving. It idles rough and surges while going down the highway. BTW, the engine was replaced with a replacement engine at some point.

I got to the parts store and they checked the codes. It had a lean code, and an O2 sensor code. I went ahead and got a new O2 sensor and CTS and got those installed. The old O2 sensor was welded directly into the exhaust

After changing those two things, it still idles rough. I took it for a quick test drive and I didn't notice the surging.

I have not checked the timing.
I have not hooked up my computer to see what the ECM is reading.

I did notice a few peculiar things. There is a knock sensor on the passenger side, but nothing plugged into it. I found some information that maybe some 1 ton trucks did not use knock sensors. According to the wiring diagram I have, the knock sensor wire should be dark blue and I did not see one.

I do (however) have a green wire running along the top of the passenger side valve cover that is not connected to anything. Additionally, in the passenger side head, there is some sort of sensor, but nothing hooked up to it.

When I looked at the injector spray pattern, at idle they seem to be spraying A LOT. Enough to have liquid gas running down the sidewalls of the thottle body, above the blades.

It also smoking a decent amount kinda a whitish blue color. I'm assuming cause its running rich, but could be burning oil as well.

Let me know what you think I should check first.

(additionally, I have to change out the rear u joint. I got the A/C system charged and blowing cold air.)

[speedygonzales]

Rich running smoke is always black. Any smoke with a blue tint is oil. You should check the oil right away for the smell of gas. Chances are good you have crank case dilution.

I don't see how you got a scan at an auto parts store. I have never seen a store that could do earlier than OBDII. A common issue on the Camaro website prior to 96.

My suggestion to you is first track down the actual GM shop manuals not aftermarket to check wiring and sensors.
http://www.helminc.com/helm/Result.a...elected_media=

Check the condition of the ignition system not the least of which is the cap and rotor.Plugs of course. Get the manifold for a fuel pressure gauge and check pressure also, right after you change the fuel filter.

[Ackattack]

A adjusted the timing tonight. It was off the balancer, set it at 4* (454 call for 4* unlike the 350s). It's still idling rough.

I broke out my obd1 cable and did a little logging (then my computer died). The new cuts was working, O2 sensor working. The BLM was less than 128 which I've read means it's rich.

That's about all I got done tonight.

Fuel pressure gauge adapter and factory service manual is on their way along with all new steering components.

I got the rear u joint changed last night. All clunking is gone.

It's coming along pretty good for just a few days.

[Ackattack]

Another update: got the fuel pressure adapter installed and the fuel pressure is 11 psi. The spec is 9-13 psi, so this sounds good.

I played around with the egr valve, and when I pulled it up, it was kind of tough to pull up and then came back down slowly. Kinda seemed like it was dragging a lot. It was getting late so I came in. I'll check/test this and the solenoid next.

I did do some reading online, and I believe my green wire is my auxilary fan wire, and is supposed to be hooked up to that temp switch in the passenger side head.

[oldertruckfan]

how easy does the truck start? could the rough idle be due to the distributor being off a bit?

[Ackattack]

It doesn't fire up light a new truck does. Kinda like its carbureted.

By the distributor being off, do you mean off a tooth or just not timed right?

[oldertruckfan]

if its been loosened and moved that can make for a rough idle, and also hard starting

[Ackattack]

OK, over the last few days I've gotten a few things done.

I changed the cap and rotor. I also repositioned the distributor; it was 1 or 2 teeth off. The plug wires are newer and look fine. I set the timing at 4 degrees again.

I pulled the number 1 and number 2 spark plugs. #1 was black and sooty as if running rich. #2 was wet.

I changed the map sensor.

I pulled off the TBS, and pulled it apart. I cleaned the IAC, put in a new reg. diaphram, etc. etc. Then today I put in new injectors.

I pulled the EGR and checked it out. I did a little cleaning on it, but it didn't look too bad. I checked the EGR valve per the factory service manual and it all checked out good.

I found the knock sensor connector. It was sandwiched in between the starter and the block. I dropped the starter down, pulled out the connector and plugged it in.

During my test drive tonight my BLM is <100. I'm using WinALDL and I'm not sure which ECM option I should use. I pulled out the glovebox and the "Service number" on the ECM says "1228747"

So its still running rich. Any other suggestions?

[ChevyTech]

You should have pulled codes by jumping the a A & B terminals of the ALDL instead of trusting a parts store scan tool.

There should have been a knock sensor code in the ECM memory, if it was not connected. It should have set a code for being unplugged at start up.

As soon as the engine reached operating temperature the ECM will run a self test of the knock sensor. You should test the coolant temp reading with the WinALDL and see what it shows.

The BLM is to low because the system knows it is to rich and is trying to lean out the mixture.

The ECM number looks right for your truck if it does not have a 4L80E.
What do you have for a transmission?
No overdrive will contribute to the low miles per gallon.

1228747 ECM
Application: 1989-90 truck 5.7 V8 TBI “K” L05
1991-92 truck 5.7 V8 TBI “K” L05 w/o 4L80E
1990 truck 7.4 V8 TBI “N” L19
1991 truck 7.4 V8 TBI “N” L19 w/ MT

The MAP can make it go rich also. Make sure the MAP senor is getting good vacuum to it. Get readings with WinALDL. Get a idle reading and post it

Get a coolant temp reading with Win ALDL, with engine warmed up.

Is the exhaust system in place without leaks?

Does the truck have a smog (A.I.R.) pump?

[Ackattack]

No air pump

The knock sensor code hasn't showed up at all and I've reset the ecm by disconnecting the battery ground several times.

Yes, it's a turbo 400 tranny.

I'll post the temp and map readings later. I know the CTS reading was similar to the temp gauge on the dash. The map reading at least made sense based on the description in the factory service manual (reading increased as you open up the throttle more)

[Ackattack]

Map at idle was 42 kpa

198 on temp

I tested the vacuum line from the Tb to the map sensor and it was good.

I then broke out the starting fluid. I spayed a little across the top of the TB and it acted like it was going to die. Then I sprayed around the hoses and no change. I sprayed around the base of the adapter and almost got it to die again. I'm hoping this is my vacuum leak that is causing all of the issues!

[ChevyTech]

42 kpa would equal 12.40 inches of vacuum. That is low, and will make it rich.

I would test the engine vacuum with a vacuum gauge and see what it getting to the MAP sensor when it is giving that reading. Also test the vacuum at another spot to see if get the same reading.

The temp reading is good.

If you think you have a vacuum leak you could look at the IAC count. If it has a good size vacuum leak the IAC count will be zero. But, that is not the only thing that can give it an IAC count to low so just use that as a check. GM gives a wide range for an acceptable IAC count but I like to get it around 20 with a fully warmed up engine at idle with all accessories off. The IAC count takes time to relearn its position after making changes that affect the idle, or you had the IAC unplugged with the key on. Driving the vehicle at highway speeds will invoke a relearn

When you set the timing did you have the set timing wire connector unplugged?

[Ackattack]

Originally Posted by ChevyTech

42 kpa would equal 12.40 inches of vacuum. That is low, and will make it rich.

I would test the engine vacuum with a vacuum gauge and see what it getting to the MAP sensor when it is giving that reading. Also test the vacuum at another spot to see if get the same reading.

The temp reading is good.

If you think you have a vacuum leak you could look at the IAC count. If it has a good size vacuum leak the IAC count will be zero. But, that is not the only thing that can give it an IAC count to low so just use that as a check. GM gives a wide range for an acceptable IAC count but I like to get it around 20 with a fully warmed up engine at idle with all accessories off. The IAC count takes time to relearn its position after making changes that affect the idle, or you had the IAC unplugged with the key on. Driving the vehicle at highway speeds will invoke a relearn

When you set the timing did you have the set timing wire connector unplugged?

IAC counts were 12 going to town (about 5 miles) and 5 coming back home.

[ChevyTech]

Originally Posted by Ackattack

IAC counts were 12 going to town (about 5 miles) and 5 coming back home.

The system is still in control of the idle speed so if there is a vacuum leak I expect it to be small.

[Ackattack]

Using this chart:http://www.engineeringtoolbox.com/va...ter-d_460.html

my map sensor looks accurate. Using a vacuum gauge, it was pulling about 16.5" Hg at idle.

I changed the adapter gasket (it was pretty brittle) and after that I could not get it to stumble using starter fluid like I did last night.

Yes I had the tan wire disconnected when I set the timing.

With the a/c and lights off, the IAC was 0, with the a/c on, it was around 20 (18-25)

I guess I should also mention: while driving at a steady speed the truck drives perfectly fine. However for a 454 and 4.10 gears, it really lacks power. I'm not even sure if it will do a burn out, and 55 to 60 takes a long time even at full throttle. From my point of view, it's down on power. At heavy throttle, it doesn't ping or do anything weird.

[Ackattack]

After some further reading on the internet, I looked at the minimum air adjustment. The plug on the throttle body is still in place. My TPS is reading 6.5% or .8volts at idle. the Factory manual says it should be about .6V or less than 1.25V depending on which paragraph you're reading.

[ChevyTech]

I found the conversion site you posted a link to confusing.
I have many convertors in my saved favorites they all show the same result, 42 kpa = 12.40 inches of mercury.

Here are some convertors I use:
http://convert-to.com/conversion/pre...-in-of-hg.html
http://www.csgnetwork.com/pressconvtable.html
http://www.endmemo.com/sconvert/kpainhg.php


42 kpa is too low and will make it run rich.
I think you can toggle WinALDL to get it to read out the results in different formats.

If the vacuum gauge you put on it shows 16.5 inches of vacuum and the ECM show 42 kpa something is not right with the MAP sensor.

Will the old MAP sensor (that you replaced) give the same reading, if you put it back on?

If it has been running rich for some time the valves can develop very heavy carbon deposits on them, which can have a big affect on engine performance.

It would be a good idea to test for restricted exhaust.

You may want to test the compression and see if the combustion chambers have heavy carbon deposits.

The IAC count should never hit zero. At zero the system has lost control. Maybe it does have vacuum leaks.

.8 volt for a TPS reading is within spec and should give no trouble.

[Ackattack]

I wonder if our discrepancy in the vacuum pressure is due to gauge pressure vs absolute pressure. I am assuming the MAP sensor (Manifold Absolute Pressure) reads in absolute pressure.

Absolute pressure = gauge pressure + atmospheric pressure (with guage pressure being negative in a vacuum scenario)

I was thinking about this last night as I went to bed and it seems that a vacuum leak would cause this. What is a "normal" vacuum reading for a tbi 454?

Also, while I was changing out the gasket for the throttle body adapter, I had to disconnect a hard line from the back corner of the adapter (not the coolant hoses) that ran back towards the transmission. I didn't have a chance to investigate where this goes. I think the transmission connection is right behind the TB connected directly to the manifold (not the adapter).

Another thought was about the charcoal canister?

[ChevyTech]

You are right the sensor is named MAP for Manifold Absolute Pressure.
In the early CCC days the vehicles had a barometric pressure sensor that is now incorporated into the MAP sensor.

I have never used WinALDL but I have help several people track down problems on the message boards when they were using WinALDL. I just looked at my WinALDL notes and found I had written “The MAP Kpa is a calculated difference number and is very misleading.”

I am used to looking at MAP readings as a voltage. The specifications are very vague because the altitude / air pressure affects the reading. Spec is 1 to 2 volts at idle.

First check I do on a MAP is see how high the voltage will go KOEO (Key On Engine Off) which should be over 4 volts, which is also a not very specific spec because if varies depending on altitude / barometric pressure.

Take a MAP reading on another vehicle in your location so you know what is normal for where you are. It does not need to be a TBI vehicle, but I would test it against a TBI vehicle if you have access to one. For WinALDL to work, the vehicle has to be the old slow ECM used before the transmission was shifted by the computer. This includes manual transmission TBI trucks through 1995.

I would expect to see 17 to 18 inches of vacuum at idle. Your truck's 16.5 is pretty close to what I expect.

Charcoal Canister valve failure was a fairly common on the canister valves with a diaphragm. When the diaphragm ruptures it can cause a very rich condition. Many of the older TBI trucks had a charcoal canister that had no valve and eliminated the possibility of that problem. I remember working on motor homes with a big block TBI and their charcoal canister did have a purge valve.

If your truck has a purge valve style canister, put a hand vacuum pump on the small vacuum port (control line) of the control valve and make sure it will hold vacuum.

A turbo 400 has a vacuum modulator on the transmission and that is most likely what the vacuum line was to that you described.

[Ackattack]

I compared my MAP reading to my '68 that has a 5.3L in it. I have HPtuner for it, so its the only other vehicle I have any kind of scanning ability.

The '68 read 97kPa and the '90 read 96.8kPa. So I'm pretty sure that the map sensor is fine.

I continued checking for vacuum leaks and didn't find anything. I took off the TB and the IAC valve and they look nice and clean.

[ChevyTech]

The big block TBI engines are know for timing chain & sprocket wear.

Anything lose on or in the engine has the possibility of creating knock counts by the knock sensor. This will cause the system to retard the timing because it thinks it is pinging.

See if it is producing excessive knock counts with the WinALDL you were using.

On early trucks like yours with the separate knock module you can monitor the voltage on one of the wires to see if the module is sending a signal voltage that is causing the timing to get retarded.

You could also watch the timing with a timing light and see where it is at.

NOTE: Some vehicles only have spark control when the vehicle is in gear.

[Ol Blue K20]

Subbed, my 89 K3500 gets 8 mpg, always thought it was normal....hmm, got me wondering now

[Ackattack]

I ordered a infrared temp gun, maybe one of the cylinders isn't running right. I'm also going to test the coil and see if that's not the problem.

I've never got any knock and the timing does advance when the esc is plugged in.

Maybe I'll just do another cummins swap.

[ChevyTech]

To know for sure the timing is not retarding it takes some testing or data logging and comparing to a know good data log.

I am short on time but am keeping an eye on your thread.

[Ackattack]

Tonight I tested the coil, and I couldn't get one of the readings according to the service manual (can't remember which one) and since I already had a new coil, I went ahead and changed it out.

I started the truck up and it seemed to idle a little smoother. I took the truck out for a spin and the BLMs were a little higher, but there were still several less than 100. The truck "may" have had a little better power.

When I got back from my approx 10 mile drive, I did have some knock count, 71. I don't know if that is high or normal or what. The IAC was still 0.