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Need Input

rockfoot

rockfoot

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Location
Moncks Corner, SC
I have read a lot of these threads, mainly for entertainment and education. I have enjoyed some of them and excused some of them as B/S... no big deal. I now need info from the experienced guys out there. To create a background out there so you kinda know something about me, I will attempt to describe my situation and knowledge of the diesels that I own. I have a 1995 Sierra 6.5 K1500, a 1997 Suburban 6.5 K2500, a 1991 Dodge Cummins, a Farm Trac 45 hp tractor and a 101 hp Takeuchi skid steer. The vehicle in question now is the Sierra. Bought in in Feb. this year. I am not sure of what is going on with it and as I have just retired (1 April, 2015) and just replacing a component (easter-egging) to trouble shoot is out of the question. I might not even have a problem. What was happening was that the truck engine did not feel right.. lot of black smoke, SES light coming and going... Installed a boost gauge... at first there was no boost. I suspected the vacuum pump was not working... it was. The little relay had the hoses in the wrong holes. I got a schematic and straightened out all the hoses. Then it still would not work correctly (no boost) so I did the vacuum gauge checks and found a hose with a hole in it. After the hose was replaced, the vacuum and boost was there but varied at steady RPM. Upon real close inspection, I found a bit of debris in the little hole coming out of the little relay to the waste gate actuator. Which brings up the method to tell if your waste gate actuator is working. On my '97 Suburban, if I remove the vacuum hose from the waste gate actuator, the waste gate shifts position right away... like it is spring loaded. On the '95 Sierra, it doesn't move. I have looked at different drawings and some show a spring that the vacuum is working against and some don't show a spring. I later opened up the boost actuator and found there was no spring (on the 95 Sierra). I finally made it (the boost actuator) mechanical with a spring to prove the waste gate was closed. Now, I have boost...not much. If I stomp it, it will get to 10psi. but quickly returns to about 1-2 psi... At 70 mph, I have about 1.5psi, steady cruising, no load. My 97 Suburban shows a vacuum at 80mph...(no load, stock vacuum waste gate actuator)???? I can here my 97's turbo spooling when going down the road and in traffic. I have not heard the 95 spool up yet.
Question #1... Can the waste gate valve seat (or whatever) be cut or worn or could the valve itself wear out. The truck has 245,000 miles on it.
Question #2... Does the MAP influence the ECM to add fuel as the pressure goes up? I know on my 91 Dodge (mechanical F/P and mechanical injectors), the pressure from the turbo directly affects the amount of fuel the IP dispenses.
Question #3... What kind of boost pressure should I see at 2000 rpm, no load?
Question #4... On my Suburban at 80mph and -0 boost, am I doing any damage and should I go to a mechanical actuator...or just slow down...?
Please, I know most answers are opinions from personal experiences and some answers can only be a fact. I will appreciate all input. Thanks in advance, R. Barrett, Cross, SC
 
1. if the wastegate arm moves freely when disconnected then try slapping it closed several times and see if you can knock of any carbon buildup that might be keeping it from sealing.
2. I might be off on this but I think the PCM is more along the lines of cutting fuel so as to protect the engine so it won't overboost. At least with a stock program.
3. 2000 rpm going down the hwy you won't see more than 2-3 lbs. unless you load it ie hill or trailer
4.You won't damage the engine with 0 boost unless you have lots of black smoke which would indicate a high EGT. doesn't sound right to not have any boost at 80 mph though
 
"Question #2... Does the MAP influence the ECM to add fuel as the pressure goes up? I know on my 91 Dodge (mechanical F/P and mechanical injectors), the pressure from the turbo directly affects the amount of fuel the IP dispenses."

Its been a long time since Ive even looked at the MAP, but I don't think its even hooked up to the engine is it?
The amount of fuel IP puts out determines the turbo's out put/boost.

Welcome to TTS, got pictures of your truck?
 
The other thing that I forgot to add in that first post was that the '95 acts a little wierd when I slow down. The '97 doesn't do it. When I am coasting down after running 50-70 mph, the tach goes down to about 1000rpm. When I approach the intersection or stop sign or whatever and I apply the brake, the rpm drops to about 600; then the engine "poofs" about 3 times and the tach jumps to 1000 momentarily and then drops to 600. Wass-up wid dat????
 
On your last post, the '95 is doing the correct thing, stays around 1000 or a bit more when coasting, then drops to idle rpm (end of engine braking) when you hit the brake. The jumping back to 1000 and down again I would guess would be a brake switch about to go bad, very common problem.

On your boost question, the fact you build to 10 psi momentarily tells you your waste gate must be sealing OK. To prove it out I'd either crank your spring mechanism way up or wire it shut, then see if it holds 10 psi. I'm guessing it still drops, which would lead you to think the PCM is dropping fuel.
 
When you touch the brake the TC will unlock. Try going 55 with left foot touch the brake and you'll see TC unlocks.
 
OK.. Let me think about that a while... didn't know that was happening... (I remember now; the TC locks up at about 52mph) I did hit the brake while going 55 and the RPM did change..... I guess that is why the engine slows down a little when I hit the brake. What I am thinking is that the drag of the axle input keeps the RPM up until the TC is disconnected... I thought it was a signal from the ECM. Oh well.... After thinking about it... what Dave01 said... brake switch. Thanks.... Still not comfortable with that silly Turbocharger. Is there a way to check the timing without owning an analyzer of some kind? If this was a as engine, I would have checked the timing a long time ago. Not sure if you will understand but the engine feels as if it holding back.. like the timing was retarded... anyway.. the thing runs good but I think it should run a lot better... milage is hanging abot 17.5mpg. No load, flat, low country hiways.
 
Do you know what axle ratio you have in the K1500? Sounds like it's running well, as for the holding back feeling, these 6.5's don't leap forward when you step on it, they just pull steady and strong. If you are running over 2000 rpm on the highway, which you would be with 3.73 gears that you likely have, you can always feel the engine running hard even on level ground. My 4.10 gears are up over 2400 rpm when I'm over 70 mph and while there may be a light load on the engine, it certainly feels wound up, can't tune it out. I would guess your Suburban has 4.10's.
 
I get good milage with the Suburban... It is not 4.10... it is higher than that as I crawled under there and checked it when I bought it. It was a 3. something... probably 3.73. The Sierra is turning about 2100rpm at 70. I bought a wore out work truck for my brother (1996 6.5 t/c) and it had a 4.10 in it and it really ran good but the rpm was always higher than the Suburban. One thing is that in both the Suburban and the Sierra, the speedometers are off a bit (according to GPS). The Sierra reads about 7mph too high. The Burb is about 3mph high. Had to laugh at one of the threads where the guys were video taping there speedometers while they performed a hard acceleration and bragging about getting to 60 mph in 10 seconds or 12 or 15 seconds... I own two of these things and both speedometers are wrong.... So when I get to 60, I am only going 53... lol... those videos weren't proof of anything.... (not trying to start no s**t) Just an observation.
 
Not sure what has happened but the '95 Sierra turbo started working as it should or at least how I think it should. It may well have been a carboned up waste gate valve/seat... It holds a steady 3.5 lbs at 70mph and increases any time I accelerate... It still does that "pooot-poot-poo" when I hit the brake while coasting down to a stop from hi-way speeds. Again, that is probably the brake switch... yet to be changed out...
 
Pulling DTC codes is an important part of diagnosing problems without code information it all becomes a guessing game that can get very expensive akin to pissing up a rope at times.

MAP aka: Boost Sensor tells the pcm the diesel needs more fuel according to boost level that boost signal is converted into voltage the "higher the boost the higher voltage = more fuel." However too much boost it will drive the pcm to defuel and go into limp mode 3 ways around this one (1) is to install a 3bar MAP the second (2) is a tune third (3) is to make a resistor pack to fool MAP.

Also, when you step on the brake the pcm defuels this can be felt inside the vehicle and most notability going down hills with no throttle input to the point of zero fuel.

A MAF sensor measures mass air flow into diesel and tells pcm it can trim fuel up/down according to other information from other sensors in the mix.
 
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Most all of these speedos are off from the factory. Mine is off by about 3MPH until I get up to 65. 67=65, but 70=70, and 75=77. Below 65 though it is off by 3MPH. And in my 0-60 videos, it hits 60 WAy before the speedo does as these speedos cannot move fast enough to keep up with mine(I have a DURAMAX powering mine though, so my 0-60 times are ab it quicker than waht most are used to).
 
FellowTraveler said:
Pulling DTC codes is an important part of diagnosing problems without code information it all becomes a guessing game that can get very expensive akin to pissing up a rope at times.

MAP aka: Boost Sensor tells the pcm the diesel needs more fuel according to boost level that boost signal is converted into voltage the "higher the boost the higher voltage = more fuel." However too much boost it will drive the pcm to defuel and go into limp mode 3 ways around this one (1) is to install a 3bar MAP the second (2) is a tune third (3) is to make a resistor pack to fool MAP.
He's discussing an S engine with his 1500, so it uses A MAP sensor mounted on the firewall to provide altitude information to the ECM as well as to tell the ECM that there is vacuum present from the vacuum pump to operate the EGR. And all of the 6.5's used a 2 bar MAP AKA boost pressure sensor mounted in the intake. And the boost sensor has virtually no bearing on fueling, it is there so the ECM can control boost, or if it hits an overboost condition it will pull fuel. When the guys were working with DIY tuning, they found the boost sensor did not restrict max fueling in any way unless boost went over what was in the boost table.
Also, when you step on the brake the pcm defuels this can be felt inside the vehicle and most notability going down hills with no throttle input to the point of zero fuel.
What you are talking baout is decel fuel cutoff, and it isn't dependant on hitting the brakes. The brake switch triggers the ECM to unlock the torque converter, and lowers the engines RPM's down. Decel fuel cutoff when it cuts fuel is when the ECM detects that the engine doesn't need any fuel because it is being used for braking. Autos don't really do this very much as GM wanted to protect the hollow trans input shaft from being sheared, so the ECM never really fully cuts fuel to the engine.
A MAF sensor measures mass air flow into diesel and tells pcm it can trim fuel up/down according to other information from other sensors in the mix.
The MAF was used on 6.5's with an S engine with OBD2 emissions. It allowed the ECM to see a drop in air going into the turbo so it new how much exhaust gases were going into the engine from the EGR valve.
Click to expand...
In red
 
And to the OP, the fueling in your 91 DODGE is actually metered better to boost than the 6.5's is. CUMMINS had to use a aneroid on the inejction pump to control max fueling so as to reduce smoke output from the ENGINE. GM decided to use such a small turbo that it was boosting right off idle simply due to how small it was. This combined with a max fueling table VS throttle input limited smoke output. GM essentially made there electronic injection system mimic that of a mechanical injection system, but added in diagnostics, electronic boost control, and a few small changes to limit bottom end fueling. vif you seen the fuel and timing tables in the ECM code, you would scratch your head and say why? It basically mimcs the operation of the DB2, just with less fuel at lower RPM's.
 
I thought that relay on the firewall was part of the egr system... The MAP sensor is in the output of the turbo. On the dodge, there is a diaphram that feels the boost pressure that moves the fueling pin down and up to give more or less fuel delivery. When the Sierra goes "pooot-poot-poo", the tach jumps to about 1000 at the same time.
 
rockfoot said:
I thought that relay on the firewall was part of the egr system... The MAP sensor is in the output of the turbo. On the dodge, there is a diaphram that feels the boost pressure that moves the fueling pin down and up to give more or less fuel delivery. When the Sierra goes "pooot-poot-poo", the tach jumps to about 1000 at the same time.
Click to expand...
The one mounted in the intake after the turbo is refferred to as a boost pressure sensor. it is there solely to sense how much boost teh turbo is putting out for OBD1 trucks, and OBD2 S engines(OBD2 F engines also use it to tell the ECM altitude readings). The DODGE uses an aneroid mounted to the injection pump. This is what limits or allows max fueling dependant on boost. And the firewall mounted MAP sensor serves different purposes depending on the engine and year. OBD1 F engines used it to tell the ECM altitude readings, OBD1 S engines used it to provide altitude readings and to tell the ECM how much vacuum was going to the EGR valve, OBD2 S engines kept it to tell the ECM vacuum readings to the EGR valve(but they also had the MAF sensor mounted in the intake before the turbo to make sure of how much the EGR was flowing), and OBD2 F engines do not use a firewall mounted MAP.
 
rockfoot said:
I get good milage with the Suburban... It is not 4.10... it is higher than that as I crawled under there and checked it when I bought it. It was a 3. something... probably 3.73. The Sierra is turning about 2100rpm at 70. I bought a wore out work truck for my brother (1996 6.5 t/c) and it had a 4.10 in it and it really ran good but the rpm was always higher than the Suburban. One thing is that in both the Suburban and the Sierra, the speedometers are off a bit (according to GPS). The Sierra reads about 7mph too high. The Burb is about 3mph high. Had to laugh at one of the threads where the guys were video taping there speedometers while they performed a hard acceleration and bragging about getting to 60 mph in 10 seconds or 12 or 15 seconds... I own two of these things and both speedometers are wrong.... So when I get to 60, I am only going 53... lol... those videos weren't proof of anything.... (not trying to start no s**t) Just an observation.
Click to expand...

I guess you completely missed the point of "back to back" runs showing improvements over stock "can't get out of it's own Fing way" with the same inaccurate or not speedometer. If your speedometer is inaccurate most state laws require YOU to FIX it. Note tire wear will affect readings. Just an observation as my speedometer is accurate to within tire wear and GPS.

It isn't so much as bragging as it is showing people what can be done with the 6.x diesels that most regard as a turd and don't even try. This same turd reputation is why you got your 6.5's so cheap over the Dodge Diesel. No other way to prove what the improvements have done aside from the "useless for towing" track or getting dyno numbers.
 
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