GMC Sonoma Extended Cab Pick-up

1999 GMC Sonoma Extended Cab Pick-up Heating / Cooling System Malfunction  Always

for several months position#4 on the heater fan control did not work. I only had 3 fan positions. Yesterday the three fan speeds that were working quit.Is this a resistor problem or a switch problem? Were can I get the needed parts? Thanks

First check the fuse, then locate the fan.. there is a group of wires that connect to the fan (it should be behind the glove box) with a test light see if you have voltage.. if u have voltage.. the motor is bad (about 45.00) if the switch is bad.. not sure.. it is a dealer item.. but i have had great luck taking them apart and cleaning them.. let me know if i can be more help. Al

you didn't mention the resistor, in your opinion is that not a player? Why would I loose fan speed #4 several months ago and then just yesterday loose the other three positions. I want to be as sure as I can before I freeze my butt off working on this thing. Thanks!!

If you have a various speed controller for your blower motor (more than 4 speeds), and you have problems with speed settings (the S at the end it the ticket) then you may have a resistor (aka varisistor problem) but with a 3 or 4 speed motor it is normally a case of the motor burns out the wiring to a specific speed setting.. and u loose only that one set point, then u loose another or the ground fails and the entire blower stops working. Again I refer to testing for voltage at the wiring to the blower motor to verify this.. yes it is cold and I dont recommend more time in the frost than needed. AL

1999 GMC Sonoma Extended Cab Pick-up Electrical / Lighting Systems Stalling When driving When warm 

GMC Sonoma 4.3 Liter V6, 2WD. My engine will cut out and die when it gets to normal operating temperature after about 15 minutes of driving. Does this consistently every tday for last week. After cutting out will not start again until engine sits for at least 60 minutes. Getting spark and fuel pump turns on sometimes but not always after engine dies. 12 months ago replaced alternator, ignition switch, fuel pump relay. Last winter my water pump was leaking and that caused the coolant system to get corrodid and the engine almost overheated. Cleaned all hoses, reservoir and fushed out radiator and entire system. Also installed new water pump. Just installed new ignition coil and that did not help. I have already tested a new crank sensor and Ignition Control Module and that did not help as well. I have heard this could be the oil pressure switch/sensor, temp sensor, EGR Valve and all the things I have already tested. Last summer I was out of commission with "experts" trying to find the problem of my engine going nuts and dying randomly which turned out to be the ignition switch. I do not want to suffer thru that again. Any help would be a blessing. Thank you in advance for your help.

You have stated you have spark (hopefully at all cylinders).
You also need to have the check engine light coming on when key is first turned on (as it normally does). It probably does so the next to check is injector pulse. Use a noid light (available inexpensively at your local parts store) to check for fuel injector pulse.

What is missing? Let me know.

Dear Mark,

Thank you for the prompt response. The check engine light will come on, as normal, as I turn the key forward to start the engine. It does go out as normal too.

The problem started a hot day last week when the ABS light went on, the RPM meter jumped up then down a bit erraticely and the engine almost stalled. I then pressed the gas pedal and felt as if the engine was revving up to get going, I'd compare it to trying to start off in 2nd or 3rd gear in a manual transmission. Then the truck stalled and would not start again until 7 hours later when I came back to get it. Now it simply starts up fine, after about 15/20 minutes the RPM meter jolts and the engine dies then won't restart.

I will get that part you recommened and test the fuel injector pulse. I read quite a few posts at the all-parts site and it looks like it may be the fuel pump. But I don't know why it would turn on only sometimes when hot though. Would you suggest I try to test the fuel pump pressure when it's hot and stalls out too?

The fuel filter I would assume would not cause this heat related problem. What about the oxygen sensor or temp sending unit?

Thank you again Mark, I went thru hell with this truck last year spending over $900 last summer for a $70 part.

Sincerely,
Michael

If you have a fuel pressure gauge, by all means test pressure. If forced to guess, I don't think the fuel pump is the problem.

The oxygen and temp sensors can not cause or no start UNLESS (and still not always) they are shorted.

And just to make sure you understand, the check engine light function must be checked during the no start period to be accurate.
If you have an autozone nearby they will check for any stored troublecodes in the PCM (computer) free of charge. If they find any trouble codes it's important to give the actual trouble code designation (IE- P0300, P0420, etc and NOT their description of the code as their description is not always accurate and is often misleading).

Sorry about the wrong name, I thought your name on the email said Mark.

Anyway, I hope you don't mind me sending you more information. I love this virtual Mechanic stuff. If you feel at any time I need to pay you more money for your service please let me know.

I went to Autozone and had it tested this morning and no codes came up. Checked both at start and also when engine stalled then cut out.

I noticed 2 more detailed things. The engine needs to heat to a temp (on the dash gauge) of about 190-200. After it dies I can start it back up immediately and then it stalls and dies again. Fuel pump working okay then. I then keep trying to restart and will turn and spark but will not start. After a few tries the fuel pump does not turn on as well. Fuel pump will not turn on until cool again.

Also, I noticed that the clock on the radio seems to reset every time. To me that signals an electrical failure which may rule out may other options.

I purchased the fuel injector testor you recommended and will test this afternoon.

Any comments / suggestions are worth their weight in gold to me. I greatly appreciate your help. If there is anything I can do to help you maybe grow your business let me know.

Thanks,
Michael

"The oxygen and temp sensors can not cause a no start UNLESS (and still not always) they are shorted."

I made this quote earlier, aside from improper grammar it's also technically incorrect. The temp sensor can cause a no start on occasion (say it's -20 degrees and the sensor tells the computer it's 80 degrees, the computer may not richen the fuel mix enough to start the engine in cold weather). What I intended to say was that they would not cause it to stall.

Do you have a repair manual for your vehicle?

And no rush to close the question, but your gratitude is recognized. In fact I'd rather wait and here the solution, however long it takes.

A little info on the site. I think Mark is the owner (at least he manages the site). I can't remember if this is a $5 or $10 question, but the site gets half and the mechanic gets half (which is fair in my book). I enjoy helping others, and the money is a bonus more than a wage. The amount of money offered usually has no bearing on how much I'll help someone (meaning- I don't think if someone is poor that they need less help). A positive attitude might get you a little more, which you certainly qualify for. I still find myself reaching out to those that don't, sometimes it works out.

What do you do?

I do marketing and am starting my own independent work. That is why I'd offer to help if you'd like. Let me know.

I changed fuel filter and temp sensor which needed to be done anyway and still engine cuts out. I have noticed that now the battery light stays on after starting. Still only dies after warm so not sure why it might be the charging system. I changed the alternator last summer and the battery 3 months earlier.

I do have a repair manual and it seems of little use with electrical problems. I noticed when I was looking thru records that the dealer put a new PCM in last year that was under warranty. I am going to test the fuel injectors as you recommended now.

Thanks

I keep reading that it could be a crank position sensor. I read that it reads the RPM's and just before it cuts off the RPM's usually jump up. Just a thought...

When a crank sensor fails-

1. It can fail hot and work again cold (this is common)
2. You WILL LOSE SPARK

You said you have spark... are you certain you have spark during the no spark period.

During a no start period (especially when you know the engine is capable of running mechanically... as yours is)

1. The first thing to check is for key on 'check engine light'. This confirms the computer (or PCM) is 'powered up'.

2. The next thing to check is spark to the plugs. If you have spark that confirms the crank sensor is (in turn) triggering the ground to fire the plugs

3. You have the computer powered up and spark to the plugs. The next thing you need is fuel. You need fuel supply (pressure) available to 'feed' the injectors. And then you need a constant positive voltage to the injectors and a computer signal the turns the ground on and off. This on and off signal is called injector pulse and controls the amount of fuel.

Which of these is missing during the no start? Test the first two in order. Injector pulse and fuel pressure can be tested alternatively. But if you don't have a powered up computer and spark, you normally won't have fuel anyway.
Hint- You wouldn't want to replace the fuel pump for a fuel pressure problem, If the fuel pump was not being turned on cause the computer didn't know the engine was cranking.

YOu definitely need to have the charging system checked. Many autoparts stores will do this free of charge. It's time to check grounds, battery cables, alt connections, etc. very closely.

When I am finished I would like to talk about compensating you. I have studied hard marketing and am getting my own thing going now. I may be able to help you by giving you some marketing advice.

I have the noid lite and a repair manual but cannot find the fuel injectors. I am thinking it's by the distributor cap behind the air filter. but I don't want to go taking off lines and such and mess something up. I may have to go to the library and get a different repair manual.

There are other options for repair manuals. The good ones are not free.

You can get an online service manual from GM. Cost is $20 for one day or 5 days for $45. For this price you better be prepared to print.

https://www.acdelcotds.com/transaction/subscription.asp

alldata.com DIY version is an online subscription that cost 24.95 for one year. Each additional subscription is 14.95. Most people are satisfied with these guys, the dealer site is better but then again... look at the cost. By the way, alldata will have TSB info, recall info, flow charts, etc (things you won't find in a paper manual).


Here is another site. But not timely in this case...

www.factoryautomanuals.com/

Your truck has what is referred to as 'spider injectors' if you can't find them (sorry for the confusion, I misread the year). These will be more difficult to work with. Because of this I advise you to look for reference voltage to the sensors during the no start period. I think you'll need to use a good wiring diagram and systematically check to see where you are losing power."