All Trucks, Campers, Trailers, RV's and Motor Homes - 89 Chevy problems

1989 Chevy Silverado
350 auto 4 wheel drive
TBI about 82,000 miles

Starts great, but when cold it runs bad, spits and sputters. When warmed up runs like a champ. Any ideas?

Also has an electrical problem. When the headlights are turned on, only the bright beams work. Directionals don't work either. This has the cruise control and wiper controls on the directional switch. If this switch is bad would it give the symptoms I am experiencing?

Thanks in advance, John

just a 'guess'-engine coolant temp sender problem.
(pcm doesn't know the engine os cold)
multifunction switch-'could' be at fault.or connector.

Pretty good guesses, new.

Wouldn't hurt to read codes to see if anything comes up; very easy on your OBD-I GM product:

Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical (http://www.troublecodes.net/GM/)

Thanks for the input so far. I checked the temp sensor with an ohm meter, and it did change value between cold and hot. I didn't have a thermometer though, so just did an educated guess based on the outside air temp and then checked again when the engine was warmed up.

I warmed the truck up good and then drove it. Still misfired but not too bad. Then I unhooked the sensor and drove it again. No noticeable difference between when it is hooked up and when un-hooked.

After the truck sat for about 1/2 hour I started it up and it ran perfect. That seems to be the thing with this, start it and warm it up good and when you drive it it will misfire and buck. But, if you warm it up, then shut it off and let it sit for awhile, it runs great.

I am going to check the codes and see if anything turns out, thanks for the link.

Well, here is what I did:
Read codes, and they showed that the temp sensor was bad as well as the O2 sensor.
I replaced both of those and now the truck runs bad all of the time! It doesn't run as bad cold as it did before, but when it is warm it doesn't run as good as it did before. It idles rough and when I accelerate it feels and sounds like it is missing or not firing smoothly.
I checked the plugs, thinking that maybe they had become fouled from it running bad when cold. The plugs all looked good, light tan color and the gap was the same on all of them and the gap was correct.
A friend suggested that maybe a ground wire was bad?
What is confusing me is that the truck ran so GOOD when it was warmed up. All I did was change the parts and now it is missing.
What can I check now on this?

Hmmm, not surprised the temp sensor code came up; last time I had one go bad (same motor you have) I was dead in the water. O2 sensor a little puzzling; it could have been contributing to the inital problem, but as you said doesn't make much sense that you're running worse now.

The problem with codes is that they point you down the right trail, but don't always point specifically at the exact problem. It's possible you have a wiring problem in one of the circuits (presumeably temp sensor or O2) that was agrravated by the r&r work on the sensors themselves. If you reset the computer (disconnect battery & reconnect) do the same codes come back? :coffee:

The problem with reading codes is that unless you clear all the codes and start all over and look at the codes after the check engine light comes back on - the chances of getting the right code will be less then if you did it the right way.

Unfortunately, when people insist on doing it themselves, they run into these problems.

When the GM engineers came out with this type of system, they knew that sooner or later things will go bad and when they do, you will need some way to get the vehicle home and get it to a shop to get it repaired.

The way they designed the system, they added something called the LIMP MODE. Just think about it like this, if you broke your leg, you could limp to a hospital, but you could not run a marathon on a broken leg.

Unfortunately, some people choose to ignore the check engine light and figures that it is something simple and they keep on driving it - sometimes out of necessity.

So when the first code goes off and you do not respond, the computer goes into LIMP MODE and then it set's off other codes which might or might not be the problem.

As a technician, I have seen many things set off codes. Plastic manifolds that were cracked or leaking gaskets that let air in the engine someplace other then through the PCV valve or the Throttle Body.

Could be a bad MAP sensor, could be a bad ignition coil or a bad set of wires or one of 100 things.

A trained mechanic can look at the problem and figure it out.

It could be in the steering column. I have seen times where the ignition cylinder goes bad where the theft lock goes off and the vehicle will not run and the owners threw good money after bad. Then you tell them that you put a new ignition cylinder in the car and to get rid of all the junk on their key ring and they look at you like as if you are stupid and you just kicked their dog.

1989 Surburban does not have theft lock - so please don't rag on me for my ramblings.

When a vehicle is in the LIMP MODE, it makes the engine run full rich and advances or retards the timing so it has no power and so it does not do any mechanical harm to the engine.

Clawhammer, in case you havent noticed, this is a Do It Yourself forum, yet all of your responses are the same: Take it to a professional mechanic. If these people wanted to, or could afford to they would, but they either cant or do not want to so they are here asking for our help. Why not try to help instead of trying to drum up business for pro wrenches? Just my 2 cents, let the rock hurling begin!!

'WIRE'- 'I' was thinking the same (but did not know how to address it) we want a 'hands-on' type answer- not a 2 page publication-of what 'I' call '2 million dolars worth of !useless! information'

The problem with reading codes is that unless you clear all the codes and start all over and look at the codes after the check engine light comes back on - the chances of getting the right code will be less then if you did it the right way.

Unfortunately, when people insist on doing it themselves, they run into these problems.

When the GM engineers came out with this type of system, they knew that sooner or later things will go bad and when they do, you will need some way to get the vehicle home and get it to a shop to get it repaired.

The way they designed the system, they added something called the LIMP MODE. Just think about it like this, if you broke your leg, you could limp to a hospital, but you could not run a marathon on a broken leg.

Unfortunately, some people choose to ignore the check engine light and figures that it is something simple and they keep on driving it - sometimes out of necessity.

So when the first code goes off and you do not respond, the computer goes into LIMP MODE and then it set's off other codes which might or might not be the problem.

As a technician, I have seen many things set off codes. Plastic manifolds that were cracked or leaking gaskets that let air in the engine someplace other then through the PCV valve or the Throttle Body.

Could be a bad MAP sensor, could be a bad ignition coil or a bad set of wires or one of 100 things.

A trained mechanic can look at the problem and figure it out.

It could be in the steering column. I have seen times where the ignition cylinder goes bad where the theft lock goes off and the vehicle will not run and the owners threw good money after bad. Then you tell them that you put a new ignition cylinder in the car and to get rid of all the junk on their key ring and they look at you like as if you are stupid and you just kicked their dog.

1989 Surburban does not have theft lock - so please don't rag on me for my ramblings.

When a vehicle is in the LIMP MODE, it makes the engine run full rich and advances or retards the timing so it has no power and so it does not do any mechanical harm to the engine.


What a bunch of crap. I will agree with the last two posters. Your ramblings that really don't have anything to do with the post are getting somewhat annoying. A lot of us here probably do or have worked in this field for a long time and are here to help people with their issues, not tell our life stories.

Okay, enough of the bickering; let's get back to the matter at hand. :coffee:

A professional mechanic, goes to school to learn what I am trying to teach.

If you go back and you read my post, you will read how the codes works in the computer and how to read the codes and how to clear the codes with a code reader and also to re read the actual codes.

A real mechanic knows how to check for Vacuum Leaks, knows that you use the computer to do diagnostics's and not just a ohm meter.

A real mechanic doesn't drive a vehicle when it is broke. They take it offline and repair it properly.

I have not worked in 3 years and I have had no income in 3 years, no public assistance and no Unemployment Compensation - so anytime you want to explain to me what broke is - and anytime you think that you know more about being broke then I do - please feel free to explain it to me.

The situation here calls for real world experience and not just a set of tools and advice from someone on the internet.

No one here has explained how the LIMP MODE works to this guy and most of you didn't even know what it was until I told you. Then you come on and attack me and my post.

I didn't say the guy had to have the work performed by a trained mechanic, I just said that he could take it to a mechanic and have it diagnosed and then decide how he wanted to repair the problem. Most times by the time the mechanic tears it apart, it costs little to put the actual pieces on the engine to make it work again.

I am going to check the codes again, but had one more question. The code said that the speed sensor for the speedometer is also bad. Can this affect the running? As I said before, what confuses me so much is that the truck ran so good (when warm) and after changing the "bad" parts, now it runs worse when warm. I should have mentioned before that the left side of the dash doesn't work. The heat gauge, and the oil pressure gauge as well as the speedometer do not work. The previous owner put in mechanical gauges for the oil and temp. I assume that since the speed sensors show up in the trouble codes that it must have something to do with the running.

As to the conversation about going to a mechanic or not, someone mentioned that this is a "do it yourself forum" and I am a do it "yourselfer". I paid $700.00 for this truck, and our mechanics charge about $50.00 per hour and all of the ones in my area are not very trustworthy. They have most people at their mercy because most people can not fix their own vehicles any more. I can't afford to pay someone that much money to track down a problem. I had the trouble codes read at a mechanic yesterday on my 98 Ford Ranger. Took him about 15 minutes and he charged me $30.00. In years past, I could bring a vehicle to a shop and the mechanic would give me a pretty good idea what was wrong with it. Now they all say the same thing " Bring it in and I'll take a look at it when I can". In the case of this Chevy, a shop could easily charge me more for repairing it than I paid for it. And a truck this old just isn't worth it, at least to me. And that is why these help forums are so important. It can, and many times has, made the difference between someone fixing their vehicle and someone having to junk it becaise they can't afford a pro to do it.
I am a professional carpenter and cabinet builder and have offered much advice on woodworker forums that has helped others. Woodworking comes natural to me and at times I can't understand how someone can be confuse by something that seems so simple to me. Mechanic work doesn't come as easy to me, and what should seem so obvious to someone else may not make sense to a non-mechanic.
That's all I have to say about that. I do appreciate all the advise I get here, and thanks.

I think the point that has been missed with some of claw's responses is he is trying to help you understand what all is going on and how an untrained person will have a heck of time trying to figure out a problem that even a trained mechanic is not just going to walk up and lay his finger on the exact problem in 5 minutes.

I have been a tech for Gm for many years, im certified as "world class" which is the highest cert you can get from gm. The problem you have layed out in front of us has so many varibles that there is no way I can give you an acurate diag. You may or may not have a code stored in the system, if your failure is due to a sensor problem then you have lucked out, but if the failure is related to what we call "base engine" then you will need someone trained or get educated yourself to repair.

I understand DIY and the people who enjoy the work and saving money, but an accurate diag will save you far more money in the long run that just hanging parts on because ou read online that it might fix it.
Pick up the phone and make some calls to independent shops in your area if you want to save some money, find out their diag rate per hour and ask how long the "driveability" guy has been working there.
I am a gm service writter/shop foreman/part time service manager. I hate to see someone spend money they dont have to cause its just bad for the GM image and we all know GM needs as much help as possible.
get a diag and let us or me know and I will help you in anyway I can

Sounds like the fella that had the truck did some mods to it before you got it so now its really going to be fun.
1ST i would check and make sure all battery cabels are clean and tight at both ends, no corosion and nothing loose.
2nd get a can of b12 carb cleaner, while its runing shoot some around the tbi unit base and see if you can hear the engine rpm's change, also spray some around the intake where it meets the engine and any vac. lines. this will tell you if you have a bad line or gasket somewhere that only sucks air when cold.
there is not alot to go wrong on those 89's so it should not take to long to figure it out.
pop the air cleaner off and take a look at the spray pattern out of the injectors, should be good even flow out of both.
Thats a couple quick things to check that will eliminate some things

Well, first of all, thanks to all who replied with good suggestions. The truck is fixed, and here is my helpful hint to all who read these. Don't forget to check the simple things first.

After I replaced the bad parts and started the truck up it ran worse than before. This really confused me. I tried to get another trouble code but nothing would come up. I checked the plugs, doing it one at a time. They all looked good, light tan, no gas smell, and the gaps was correct on all of them. Started it up and no difference in the running. So I gave up. Figured I'd just sell it as soon as I could.

Then yesterday, as I was walking by it I had a flashback to when I used to do mechanic work and decided to check some of the basics such as compression, plug wiring and etc. The first thing I checked was the firing order and found out that two wires were crossed. Put them in the right spot and it fired up and ran great!

My first thought and most others too, is that I put them back wrong when I checked the plugs, but the thing is, I never took any of the wires off until I checked the plugs. And when I did, it was one at a time. Take the wire off, check the plug, and put the wire back on. I don't know how this truck could have run so good when warm with the wires crossed, or what the deal was, but it runs great now.

So, thanks for all of the help, and remember, check the basics first.