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Ivan
Ivan, ASE Certified Master Technician
Category: Chevy
Satisfied Customers: 4870
Experience:  ASE Master Tech. 20+ years experience. 9 years self employed. Expert on AUTOLAB Radio Show
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Hi i have a 97 chevy 1/2 ton 4wd pickup has a 350 engine aut

Customer Question

Hi i have a 97 chevy 1/2 ton 4wd pickup has a 350 engine auto trans and i cant get the cam sensor to adjust correctly. I have a solus scanner and have adjusted many cam sensors, but this one won't run descent unless i keep it around -29 deg. When i set it at 0 deg and try to start the truck, it kicks back on the starter like the timing is to far advanced. When i do get it to start, i set the cam sensor at 0 deg and try to quickly rev the engine and the distributor rotor gets near number 8 cyl and fires it and spark knocks. I have tried crank sensor,cap,rotor,another distributor, module on coil bracket. I tried another computer out of a different truck. I didn't expect it to run at all but it did start and run, but it didn't fix the problem. It has ac delco plugs i have watched all sensors and compared them to my truck which is same year and model 30 hours invested and have got no where. Hope you can help Thanks Jack
Submitted: 5 years ago.
Category: Chevy
Expert:  Ivan replied 5 years ago.

HelloCustomer are you using the procedure from any of the information systems? Also what was the original symptoms that lead to this issue?

 

Your JA Expert,

Ivan

Customer: replied 5 years ago.
What Procedures are you talking about? The truck had a new engine put in it from GM. It ran fine then one day it had a miss. The boy took the truck back to GM and they said the heads were messed up, so they replaced the heads and still had a miss. Then he takes it to get it inspected and it fails because the check engine light is on because of the timing. I set the timing to how the scanner says to, but when it's set to 0 deg it kicks back on the starter. At idle it seems to have a little pop through the exhaust.

Thanks
Jack
Expert:  Ivan replied 5 years ago.

Jack see if this procedure helps or is any different from the one you have been using. Let me know.

 

Ivan

 

graphic

Expert:  Ivan replied 5 years ago.
Jack also, what code is being stored with the check engine light?
Customer: replied 5 years ago.
P1345 Crankshaft Position (CKP)-Camshaft Position (CMP) Correlation
Customer: replied 5 years ago.
That is the procedure i have used and i get it set to 0 deg, but it kicks back on the starter so hard it acts like the timing is to far advanced. And when it does run when its set to 0 deg, it revs up slow and pops through the exhaust and intake
Expert:  Ivan replied 5 years ago.

Here is the troubleshooting tree for the P1345, You may have a faulty cam or crank sensor that is causing your dilemma. See where this leads you. Remember if the crank sensor is not proper, the cam synch will not be correct, and vice versa.

 

graphic

 

Customer: replied 5 years ago.
I have tried that troubleshooting tree too. I have alldata and still no luck. I have replaced every sensor. Still no luck
Expert:  Ivan replied 5 years ago.

How about this and look at the next one too. I also found a revised procedure listed as a TSB. Look at this. Also I'm sending you another TSB on my next post. See if they help.

 

graphic

Expert:  Ivan replied 5 years ago.

Here is another.

 

graphic

Customer: replied 5 years ago.
I have replaced all sensors so i dont think thats the problem. How much play in the timing chain is too much? I can move the crank about 7-10 deg before the distributor starts to move.
Expert:  Ivan replied 5 years ago.

Wow, you found your issue. It shouldn't be more than a couple of degrees. 10 degrees is huge. This truck may have jumped time and the computer is trying to do everything it can to keep it running. A compression test may back you up on that one. 10 degrees if very large and I think you are there. How many miles?

 

Below is what I was about to send before you posted.

 

I've been looking on IATN and I have 2 suggestions based on what I saw, One is valve adjustment. Some overtightened valves. The second is a faulty distributor. Several posts indicated even though everything looked ok, the distributor replacement was the fix.

Customer: replied 5 years ago.
It's a new GM crate engine from GM. I think it has like 10,000 miles on it. I tried another distributor out of a running truck and still no luck. I have replaced every part i can and still no luck, thats why i'm so lost. It has been to 3 shops and noone can fix it. So now they brought it to me to fix. Whats the best way to check the play in the timing chain? Or do you think there may be a different problem?
Expert:  Ivan replied 5 years ago.
The best way, is to line the balancer on to 0 on the scale, then rotate the crank backwards and watch for distributor movement. The moment the dist. moves, look and see how many degrees you moved. That will yield exact. The other thing, is since heads were done, maybe valve adjustment will play a role. Loosen and readjust each valve and see what happens. Since you are going to be the man who fixes it, go some places that no one else has. Have you scoped the crank signal, just to make sure there is nothing wrong with the tone wheel for it?
Customer: replied 5 years ago.
I havnt scoped the crank signal, how do i do that?
Expert:  Ivan replied 5 years ago.
You have the Solus, does that have component testing in it?
Customer: replied 5 years ago.
Some, but i dont think i have seen anything about testing crank sensor
Expert:  Ivan replied 5 years ago.
I have the Modis, so forgive me if I don't know exactly what is on the Solus. On the opening menu, see if it has the options for component testing, like the way the Vantage had it. Do you have a Vantage or a lab scope or eqivalent?
Expert:  Ivan replied 5 years ago.

When graphed, here is a sample of what the crank sensor looks like. The second picture is what it looks like if the cam and crank were graphed and at the same time and everything was Ok.

graphicgraphic

Customer: replied 5 years ago.
I'm not sure. I have never used a Vantage or a lab scope or eqivalent. What are they?
Expert:  Ivan replied 5 years ago.

The Vantage was a diagnostic, graphing volt meter that had component testing. It's incorporated into the Modis, but not the Solus. I just check the Solus' capabilities and the Solus Pro can graph data, it's not a lab scope, but you can get graphical representations of the data. You can show the crank and cam signals at the same time by choosing their PIDs from the data list and can see if you have sync. It's obvious that something was done wrong when this motor was assembled and now it's time to find out what.

Customer: replied 5 years ago.
The engine ran fine when it was first installed. Then it started acting up and they took it back to GM and GM said the heads were messed up, so they changed the heads but the problem is still there. The new heads didnt fix the problem. I looked at the scanner and at idle i set the cam to 0 deg. At idle it says cam 0 deg and spark advance is at 25 deg. But i still have a miss in the engine and it kicks back on the starter with cam set at 0 deg
Expert:  Ivan replied 5 years ago.
Maybe you have a fuel issue, where not enough fuel is making it through the injectors. The maxi-injectors have issues, you might have a restricted tappet. Can you look at misfire data and see what is happening on all the cylinders?
Customer: replied 5 years ago.
On the misfire data page it shows no misfire. But i can hear it pop through the exhaust and sometimes through the intake. They said they put new injectors in. Fuel pressure at idle is 50 psi and when you rev it up the fuel pressure goes up. But that still doesnt tell us why when the cam is set at 0 deg it kicks back on the starter.
Expert:  Ivan replied 5 years ago.

Well you have a fuel pressure issue, fuel pressure should never go down, it should remain or go up when load is introduced. 50 psi is way below spec for either of the two systems. Look at these specs. If fuel pressure is too low it will compromise the engines ability to run, since these injector tappets release under pressure. If pressure is too low, fuel will not be released into the cylinder.

 

graphic

Customer: replied 5 years ago.
Ok. But At idle it says cam 0 deg and spark advance is at 25 deg. I guess that is right? But i still have a miss in the engine, which may be a fuel issue? But why does it kick back on the starter with cam set at 0,
Expert:  Ivan replied 5 years ago.

Yes those numbers sound right. The way that injector system works, is fuel pressure builds in the tappets that lead to the intake. When the pressure builds to a certain point, that fuel is released, strickly by pressure, not electrically. If you don't have adequate fuel to fire off the engine, the engine may kick back. If you only have 50 psi, it would definately correct the fuel pump issue, get fuel pressure up to 60 or so and see how the truck runs. The fuel pressure is definately too low, so replacing the fuel pump will not have been in vain. I think your misfire is going to be gone, after restoring fuel pressure to the proper amount, and that would explain having the problem before and after the work.

Customer: replied 5 years ago.
After i shut the truck off, should it hold fuel pressure? If i hook a fuel pressure gauge to the fuel rail and turn the key on the pressure does to 50 psi but as soon as the fuel pump shuts off the fuel pressure quickly drops to 0 psi. On my other truck after the fuel pump shuts off it holds fuel pressure.
Expert:  Ivan replied 5 years ago.
Ok, now we got something different. See if you can build pressure, then crimp off the pressure line, see if it drops, then build pressure and crimp off the return line, see if it drops. If you crimp the fee line, the fuel pump is bad, if you crimp the return line, the problem is in the fuel injector/fuel pressure regulator area inside the upper intake. If fuel pressure drops, in both conditions, remove the upper intake and see if there are traces of fuel laying in the intake, and the nipple on the fuel pressure regulator. If you see fuel there, replace the fuel pressure regulator and you should be good. Let me know what happens after you crimp the lines. It may be hard if you don't have any rubber line anywhere. If you do, great, if not, you may have to create hose, that you can insert in line and crimp those. If you have a fuel injection cleaner like a motovac, you can use those lines to do this.
Customer: replied 5 years ago.
If i clamp off the return line the fuel pressure goes from 50 psi to 80+psi, when you turn the fuel pump on. Tomorrow i'll check and see if it holds pressure. Thanks for all the help.
Expert:  Ivan replied 5 years ago.
Your welcome, let me know what happens.
Customer: replied 5 years ago.
I checked the timing and there is very little slack in the timing chain, maybe 1-3 deg. If i just clamp off the return line the fuel pressure still drops, but if i clamp off the feed line it holds 60 psi.
Expert:  Ivan replied 5 years ago.

With those results, install a new fuel pressure regulator and fuel pump. You should be perfect after that

Customer: replied 5 years ago.
Ok, Thanks. But i still have the other problem. Timing chain is fine so what should i check next?
Expert:  Ivan replied 5 years ago.
I would take care of the fuel issues and see how the vehicle responds. I think you will find your problems gone. If you still have anything, we'll pick up there and work together. Fuel deprivation can be responsible for your misfires and hard starts.
Customer: replied 5 years ago.
I understand that, but i don't think fuel is the problem to when i try to crank the engine over and the timing is set to 0 deg and it kicks back on the starter. It's like something is telling the timing to advance when i start cranking the engine over. Is there any other parts besides the crank sensor that can tell the computer to advance the timing when the engine is being cranked over?
Expert:  Ivan replied 5 years ago.
If fuel pressure is too low, the tappets will not drop the fuel into the cylinder. If there is not enough fuel the engine can behave that way. Since we know we definately have a fuel issue, let's correct it and see what happens. I find it hard to believe there is a fuel problem and something else. Remember when you told me fuel pressure goes down, that is confirmation that there is a fuel problem. Don't kill yourself looking for something else until we know the fuel system is up to par. I don't want you to waste energy until you need too.
Customer: replied 5 years ago.
I installed new fuel pump and the fuel pressure is 56 psi with key on and when i start the truck and rev the engine the fuel pressure jumps up to 65psi. The truck still doesn't run right. What sensors control the timing? With the truck running and timing set at 0 deg and i try to rev the engine it spark knocks. Then i shut the truck off and try to restart it and it kicks back on the starter.
Expert:  Ivan replied 5 years ago.

Can you look at data and see what timing advance is doing while this occurs. Does the vehicle show knocking, maybe when the engine was done, the knock sensors were overtorqued and the computer is not seeing knock, and as a result advancing the timing way to far. The crank and cam sensor are responsible. the cam sensor is in the distributor. The computer adjusts the timing based on their data.

Customer: replied 5 years ago.
When it knocks the knock sensor reads 7 degs.
Expert:  Ivan replied 5 years ago.
Does it show timing retard of -7 degrees?
Customer: replied 5 years ago.
It says knock retard 7
Expert:  Ivan replied 5 years ago.

Is the truck in closed loop? What is your long term and short term fuel trim? Could it be possible the EGR is playing a role. Maybe staying open when restarting?

Customer: replied 5 years ago.
Truck is in open loop till it warms up then it goes into closed loop. What would long term and short term fuel trim be listed under on the scanner?
Expert:  Ivan replied 5 years ago.
LTFT STFT I do believe that is the way its listed.
Customer: replied 5 years ago.

ST-Trim-1= 129

ST-Trim-2= 128

 

LT-Trim-1= 122

LT-Trim-2= 125

 

Is that what you are talking about?

Expert:  Ivan replied 5 years ago.
Those are them, and as long as they hang around those points they look OK.
Expert:  Ivan replied 5 years ago.
I just reviewed everything we just discussed. Have you changed the PCM?
Customer: replied 5 years ago.
I changed the computer and stuck it in my other truck and it ran fine. What else is there to try? I called the dealer and they said they have never heard of this problem.
Expert:  Ivan replied 5 years ago.
I don't know if we discussed this earlier. Have you done a compression test or readjust the valves to see if maybe any valves are too tight. Have you done a pinout test of the PCM with one of those pinout charts from alldata, just to see if maybe you have a bad ground to the PCM or a corrupted signal from a sensor?
Customer: replied 4 years ago.
Well well a year later we finally found the problem. Will you pay me for the answer, lol. Cool
Expert:  Ivan replied 4 years ago.
What may I ask did you find???
Customer: replied 4 years ago.
I guess when they replaced the engine they must have replaced the distributor. Well that distributor was out of a V-6. I put a v-8 distributor in the truck and it runs great now. Did you know that v-6 and v-8 distributor are different?
Expert:  Ivan replied 4 years ago.
Amazing find. A v-6 and v-8 have to be different. What did you do, try another distributor, have it work, then figured out why?
Customer: replied 4 years ago.
We checked the distributor with a distributor we knew was a v-8 distributor and saw where there was a 6 stamped in the ring where the distributor rotor bolts to on the v-6 distributor and an 8 on the v-8 distributor. Which puts the window for the sensor in a different location.
Expert:  Ivan replied 4 years ago.
Yup that will be the difference. That is something that would drive anyone crazy. Fantastic find and look at all the knowledge you gained in the process. Good job.

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