Gmc Jimmy help

Hello all i see you have a nice forum here been reading post to get ideas and not comming up with much i havent tried already.
Here is my problem. I got in my Jimmy the other day to run to the store and got a block away from home and the SES light came on and it started running like !@$*. So i turned around and went home backed it in the drive and it started running great. So i drove it to the store about 15 miles one way with no trouble. I left the store got about 2 mile away and the SES light came on again and it started running like @#^$ again. So i got it home and tried to pull the codes ( the old paper clip trick) and i could not get it into diagnostic mode. Would not flash at all just a solid light. So i traced the wire back to the computer and tried it there and still would not go to diagnostic mode. My best guess right now is the chip in the computer according to the only book i have here that covers the Jimmy(haynes). The EGR valve was recently replaced within the last 6 months. The Injector was replaced a couple months ago along with the fuel lines running under the plenum. I checked for tune up needs and it will need one soon but nothing is bad enough to cause this condition that i can see and the fact that it wont go into diagnostic mode leads me away from any tune up needs.
The Jimmy is a 1992 GMC Jimmy 4x4 wit ha 4.3 vortec CPI Vin W.
Any help is appreciated before i have to break down and spend the 100$ on the chip that cannot be returned to test that possibility.
P.S. sorry about the long post but wanted to get all info I could into it lol.
Thanks in advance.

I had a similar problem on my 94 Blazer 4.3 CMFI vin W. It was my EGR, rather than replacing the EGR, may time it's just clogged with a piece of carbon. Remove carbon and your golden.

Also, A company called "TOMCO" makes a gasket with a screen in it to prevent any chunks of carbon from entering your EGR.

Thanks but not the problem. It is clean and in good shape. Besides it would not explain the reason for not getting it to run the diagnostics. It will not even read the code 12 (No distibutor reference pulse) will not flash at all.

I don't know about the diagnostic acess problem, but I just thought that I would throw this in..... I had the same problem with my 2001 Outback, would run great for awhile, then it would run like *&^ . I put in a higher grade fuel, and that seemed to help for a while, then it went back to running like crap. It would run fantastic for a little while, then it would really screw up, sometimes I thought it was gonna die on me, then it would come out of it and run great. Anyway, it turned out to be an oxygen sensor. I had it changed, the problem went away and the Subie is happy again.
I do have a question for someone one out there, which I will also post separately from this reply. I have a 1989 Jimmy 4wd with a big 6 in it. THe transmission will just slip when it goes into drive. I can run it in 1st and 2nd, but after that it will slip. It would cost to much to re build it, and I am told that a chevy 350 turbo will bolt right up to it. Does anyone know this for sure? Can I just get a 350 tranny and swap it out? Any help would be greatly appreciated
Bob

Regarding the CPI issue. There always has to be a root cause to everything. The reason it ran like crap was because a piece of carbon would get trapped in the egr valve. Then the valve would cycle and the piece would get blown out. The cause of the carbon in the first place is excess fuel. If you are not haveing other problems you will be soon. The CPI regulator is probably leaking raw fuel into the intake. Once there it accumulates and richens the mixture so much so that the engine runs rich causing excess carbon buildup. I replaced mine with a GM unit twice and each went out within three months. I then bought a unit from LTS and have not had a problem since. The truck ran like it was brand new again.
To check with the manifold on, hook up a pressure gague right behind the intake on the fuel rail. I use an old a/c manifold. Have an assistant turn the key to the run position. The gague should shoot up to between 54 and 65 psi. If it starts leaking down, you have a leak. The system should hold pressure. Look for obvious leaks on the truck and if none are found, remove the upper intake manifold. If you see fuel in the lower manifold, stop and replace the CPI unit. If not do the pressure test again but watch the regulator in the right hand side of the unit. If it leaks fuel, replace the CPI.
Hope this helps.

as far as checking the fuel pressure, if the pressure dies down it is not always a leak. the fuel pump only runs 2 to 3 seconds when you turn the key. there is a check valve in the tank tha often goes bad and lets the fuel leak back to the tank when the pump is off

Please notice that I did not go any further than checking the regulator. After that if there is indeed a leak somewhere else on the truck it would be in the tank. The possibility of the CPI unit being the problem is very high. I have replaced almost ten of these units and not all on my Blazer. I have had come-backs too. THe regulator blows again after a short time. The fuel pressure required to open the poppets is so high that it blows the regulator. After the regulator is blown, fuel pressure leaks down quickly. I have started replacing these units with modified units from LTS. They are fitted with a later designed regulator that can handle the pressure.
Please share your experience with the check valve.

Please notice that I did not go any further than checking the regulator. After that if there is indeed a leak somewhere else on the truck it would be in the tank. The possibility of the CPI unit being the problem is very high. I have replaced almost ten of these units and not all on my Blazer. I have had come-backs too. THe regulator blows again after a short time. The fuel pressure required to open the poppets is so high that it blows the regulator. After the regulator is blown, fuel pressure leaks down quickly. I have started replacing these units with modified units from LTS. They are fitted with a later designed regulator that can handle the pressure.
Please share your experience with the check valve.what is lts site? i need the fuel injection spider

the site is http://www.lindertech.com/reconinj.htm

the site is http://www.lindertech.com/reconinj.htm
thank you.. do you know if i need to replace whole cpi unit? or just regulator? i have no idea donna

You could replace just the regulator but I suggest against it. Pay the extra money and get a unit that has been tested and is ready to drop in the hole. While you are at it, get the fuel supply and return lines that go in the intake. Yours may not be leaking but it is good practice. Once you reseal the intake you don't want to tear it all back apart again if the lines blow. Remember this is a high pressure system. It runs at about twice the air pressure as are in your tires.

ok thanks .. what do you think it will cost altogether?

I would plan on at least 300, may be more depending on what you are going to do. Also, it is a good idea to replace the spark plugs becasue they are probably fouled and also remove the egr valve and clean the passages of all of the carbon buildup.

Jesus guys, take it easy on the swapping out parts so fast. You don't even know what is wrong yet.

Take the truck to AutoZone and get the codes scanned and come back here with the code they got from the computer.

We can help from there.

Code Scanning wont tell you jack. It might come up with an egr failure when in fact there is only a piece of carbon (from excess fuel) lodged in the valve holding it open. It may also give faulty o2 sensor (because of a rich mixture) readings but these are just symtoms to the underlying problem. The key is the fuel system pressure test. You cant check that with a code scanner. The regulator problem is a known problem, a design defect if you will. Now there may be a few on the road that got lucky and their unit is still intact but the majority of the time the regulator blows. It is easy to tell once you get the upper intake off. If there is a puddle of raw fuel in the intake, you have problems. Turn the key to make the pump turn on and watch for seepage from the regulator or the fuel lines. It is easy to spot. The fuel lines are on one side of the intake and the regulator is on the other. You will have fuel on one side or the other. Pretty basic.
I am all for code scanners being a good way to quickly diagnose engine SENSOR problems which is what OBD1 looks at but there is no replacement for the ability to diagnose a mechanical issue.
As a side note, I worked at Autozone for two years as their parts pro. I know a thing or two. Especially on this motor. I just rebuilt mine, I did all but the machine work.

Yes it will tell you everything and at least point to the problem area instead of you just fumbling around throwing parts at it.

It is a computer controlled vehicle with a code system to help in this situation.

No using it is pure repair arrogance.

Your version of everything and mine are clearly different. I HAVE ACTUALLY HAD THIS PROBLEM. No matter how many times I scanned it, nothing would show up. OBD 1 does not look at everything. OBDII does. Probably what you are refering to is a '95 model vehicle. '94 and earlier Use OBD1 which looks at the sensors. The unit in question is not a sensor. It is a fuel injector. Trust me, I spent a year and a half trying to figure out what the problem was. I have provided all of the information needed to diagnose this particular component. By all means, don't replace it if it is not bad. Run the tests because this is an expensive piece, I have bought many of them. 10+

As far as throwing parts at a problem... I did that. I did that because the computer spit out a code that stated that the egr valve was faulty. This is also an expensive piece, about 160. So much for the computer being right about everything. All it was is carbon chunks getting trapped in the valve and holding it open (think that I have coverd this already) causing it to run like crap. The carbon was caused by the rich mixture from the raw fuel sitting in the intake from the leak. This being caused by a leaky regulator. I saw it leak so I KNOW that it was leaking.

Another symptom of the problem is hard starting. I would have to let mine crank for about five seconds before it would crank. I thought it was the fuel pump at first. As I learned more about the system I found out that it takes an extreme amount of pressure to open the poppets at startup. What I found out was that if the regulator blows it is not able to build the fuel pressure right away. If I remember right it takes around 60 psi to open the poppets. After the pump runs for an extended amount of time it will give enough pressure to open the poppets and start the truck.

I posted to this thread because I had to scrounge for the info on this system. This is an easy problem to diagnose once you know how to do it, and I have outlined that here. Basicly, check for fuel pressure. If with the key in the on position the pressure builds then starts to leak down you haave a leak somewhere. If the pressure dosn't reach near 60 psi, the truck will not start right away. Pulling the upper manifold off is very easy. I can pull mine in less than 5 min. Then it is a visable check. Raw fuel in the intake? Leak somewhere in the intake. Puddle of fuel on the passenger side then the regulator is leaking. Cycle the fuel pump again and watch the regulator. If it is leaking you will see fuel leaking out. If the puddle is on the drivers side then you have a fuel line problem. Probably not though becasue they are high pressure lines but anything is possible.

I have tried to be very clear on this issue. All of the information is here to check for the problem. I did not have this luxery when I had my problem. Heck the truck ran for a year and a half with no light on at all. So much for the computer telling you everything that you need to know. Computers are great. I build them in my spare time but they only see what you put into them. OBD2 is cool. If you have a miss, it will even tell you what cylinder it is.