There must be some old threads that describe in detail the workings of a wastegate for a '95 12v; if so could someone possibly direct me? I seem to be inept at searching this site. If not, I have some questions about how it works. Thank you

The wastegate is a bypass valve for letting exhaust gas bypass the turbines so that there isn't as much drive pressure spinning the turbo. This is for pressure regulation. A stock truck will get to 20psi and then the wastegate will open and this keeps the turbo from overspooling. When you get under 20psi the wastegate shuts, although it is more gradual than that, like it might start opening at 15 and be fully open at 20. This leaves the apparent quandary of the flow it bypasses and really, it isn't much. If you turn the truck up you can outflow the wastegate and drive the turbo above 20psi, in fact you can get well above it easily. The video shows you how big the port is. Turbos use wastegates because of spoolup. Old trucks used huge turbos with no wastegate at all, so the pressure was merely regulated by using that huge turbo and of course there was no way the truck was going to get a huge turbo to go past the trucks designed boost tolerances. The problem with that was unless you were really getting on it, the turbo wasn't spooling much. Then came the wastegate which allowed for a small turbo that you could spool at low RPM's and the wastegate kept it from overboosting. The stock 20psi rating is very conservative, if everything else is stock then you're good to 35psi, after that the turbo is out of it's usable air map and you are just creating heat and wearing out the turbo. That is why they make boost elbows. The wastegate is actuated using the air on the boost side of the turbo (the compressor) which pushes the actuator open as more boost is built. You can hook a compressor up and watch that happen (think I got a video of that somewhere). This video should help you out a lot. The aforementioned boost elbow works by restricting the air that gets to that wastegate by using a little set screw that relieves air, therefore relieving pressure, so instead of the wastegate seeing 20psi (and opening), the elbow can be adjusted to where the wastegate sees 20psi when the actual boost is 35psi (this is what everyone does since more boost is definitely a good thing in most instances).

Thank you for the reply. I have a pyrometer and boost gauge set up on a recently rebuilt engine. Injection pump also recently gone through by a good shop. Problem is no upper end power; lot's of torque and power at lower end, but as RPM's rise, power drops. Bosst gauge never shows higher than 10, 10.1. On longer highway hill climbs, if I holf full throttle, EGT climbs to unsafe levels. Seems I have one of two, maybe three (that i can think) of problems. Either the timing has slipped on the injection pump (easy to check) or something has gone wrong internally with same pump or waste gate is stuck partially or fully open. I haven't really examined the waste gate control, but it looks like there is some sort of rod that goes to some sort of modulator or controller. The modulator has a nipple which one would expect some sort of line to go to (vacuum?), but there is no line. Your answer helped alot, but what I am wondering is if the waste gate is stuck, how could I check it? Am I correct that this device is a controller, or am I barking up the wrong tree? In any case, what are the best things to check to insure the waste gate is working correctly? Also, I read somewhere that injection pump issues could keep the turbo boost down. I don't understand this correlation. Thank you again for your reply.

The waste gate doesn't come into play until 20psi. If it is stuck open, then that would keep boost low, but I am not sure it would keep it that low. There should be a line going to that which comes from the AFC on the back of the injection pump, if there is no line there then the AFC isn't getting boost and it is keeping it from moving the AFC arm over, allowing for full fuel. Let me just make a video of all the possible things and how to check them or else I am gonna have to write for a long time haha.

--- Update to the previous post...

Ya know, if the EGT's get up there then the AFC might be doing it's thing and allowing for more fuel so you might just check for boost leaks. The wastegate you can test by putting over 20psi to the fitting on that actuator that has no hose, just stick a hose on it and stick an air gun over it, as long as its not over 50+ pounds (which it won't be if you just hold it on there as tight as you can with your hand) then you can watch the actuator go out when you put air to it and come back when you let off. Look at the AFC on the back of the pump and see if it has an air line going to it. Vid will be up in an hour.

I don't believe there is any air line, but I will go check. Thank you very much

--- Update to the previous post...

No, there is no line, nor does there seem to be a place to attach one on the AFC on my pump (I may simply not be familiar enough with it, but I see no obvious way to hook up a line). Seems strange.

Alright maybe this will show you how it's supposed to be. Mine's a little different but hopefully you'll get the idea.

Wow, that was cool and helpful. My truck has the line to it from the the in man to the AFC, but there is no fitting for a line to the turbo (so no leak, just no feedback to the wastegate); manifold pressure should be controlling the AFC, but not the waste gate. There is a wastegate controller, a bit different configuration than yours, but it is there and so a place for the line. I need to try the air pressure test you suggested to see if it moves and ultimately determine what position it is in (open, closed, in between?). This engine was just rebuilt by a guy who now will not communicate with me. It has non stock pistons (marine?), non stop injectors (don't know). The pump was rebuilt and the fuel plate supposedly modified, but I do not know for sure what was done(this I can find out from the pump re-builder). I then paid to have the pump set up by a person the engine re-builder recommended. The tappet cover on the engine was leaking profusely when I got it back (a sign of this guys workmanship?), so I had to remove the pump to repair the leak. As I had never removed such a pump, I incorrectly guessed that the gear was aligned with a key so other than setting engine at TDC, did not check the timing. I have worked with the pump re-builder to try to come up with the best timing; the timing cover does not have the CPL (or any tag) on it. Bottom line, if I did my work correctly, because the engine (supposedly) should be in the 215 HP range, we used (I believe) 19 BTDC as a benchmark (CPL 2175 to 2023, .240 on the indicator). This I set using a dial indicator, so unless the gear slipped on the shaft, it should be very close to that (was checked and rechecked). Again, the EGT was getting up around 1050 (top of the green) and might have gone higher on hill climbs unless I backed off on the throttle, yet Boost was only 10, 10.1. Thanks again; great job on the video

Whoa, a mystery pump you say. Those pumps range from 160-215HP and if it was a marine setup then it's 370HP which I have no idea how those pumps are set up. Anyhow if you have no clue what it is then the timing could be way off. Does it smoke or anything? I am gonna assume it doesn't and the timing is fine but it is definitely something you should check out. The wastegate isn't an issue as long as you have a boost gauge so you can let off before it goes over 35 too much. Make sure it isn't stuck open like you were gonna do I don't think you could be hitting 1050 if that AFC was crapping out so I am gonna assume it works as well. There could be something wrong with fuel pressure which wouldn't really be seen down low since it doesn't need as much fuel going slower but up high I would think low pressure would show up much more distinctly as a loss in power/boost. Again does it smoke going up those hills at all?

From what I can tell looking back in the mirror, no, it does not. Its the pistons that are marine; pump is, I believe stock, although governor was supposedly modified a bit when it was sent to the re-builder so the RPM cut out is set a bit higher. Delivery pump is new (as are all filters), but there are also the electric pumps in the tanks (vehicle originally a Ford F350 gaser). Both pumps seem to be working and no difference in performance from one tank to the other. But, I have not checked delivery fuel pressure. Anyway, no or little black smoke that I can see. Thx

And no boost leaks? If any of those clamps are loose it blows right out when it gets to a certain threshold. Anyhow it really reduces to a few things. The injection pump sounds like it's working but not giving it enough fuel, like the fuel plate is slid towards the cab a bunch. The AFC only controls it to 5psi and then moves out of the way, it COULD not be moving all the way out of the way though. You can take it off (the thing I showed on that diamondplate), and test it as shown in this video (linked writeup in next paragraph). Hook it up to a known pressure and see where it moves at and it should be under 5psi. Then you can look at the fuel plate and see where it is (slid all the way back or forward). If all that checks out, there are no boost leaks, wastegate is fine, then I would check fuel pressure. The pump doesn't really dictate pressure it is the overflow valve that does, which they go out every now and then regularly. Here is a writeup on that AFC and you can see that arm that pushes on the main fueling arm to control how the pump fuels to prevent black smoke. That arm should move over like in the vid with 5psi or less. The Fuel plate also shouldn't be all the way back as that will defuel it pretty good.

Other than testing tightness of clamps, any good tricks for inter-cooler leak testing? In any case, I will go thru and check that, recheck timing, and then check plate and star adjustment. One last question; would the fuel plate set for too little fuel tend to raise or lower EGT? I want to equate it to a lean mixture, high EGT as in a gaser, but this may not be correct. Thanks so much for all your help; really appreciated. Cheers,

This is probably the best way to check for leaks, though a leak big enough for only 10psi would be pretty apparent if it wasn't a boot it would be a big crack somewhere.

Diesels run extremely lean by design (with the turbo and all). They have no control of intake air so when the intake valves open it shoves in as much air as possible. High EGT's come from excessive fuel and not enough air which is a product of low boost and too much fuel going in (which ends up in unburnt fuel seen as smoke). The speed and RPM you were going determine the EGT the most with a truck running only 10psi. I can do 10psi at 1000RPM and see 1000F pulling a trailer up a hill, yet I will be at 500F pulling the same trailer at 60 at 10psi.. Timing being off can skew EGT's a lot as well. There's a lot of factors and the symptoms are not making it easy haha. If you can describe more of how you were driving in full detail when it was at 1000F that might help.

I was travelling from British Columbia to SF Bay area of CA down rt 5. Only mentioning this in case you happen to know the route; there are numerous hills, ~7, 8 % grade that go on for at least a mile. Again, truck is an F350; it is a club cab and it was lightly loaded, so gross weight under 8K, probably 7.5K lbs. Because of lack of power, I was using full or near full throttle going up hills until I learned that if i let the vehicle slow down to about 60 MPH, it got into an RPM and torque range where it was happy. I also learned that I gained little by applying more throttle other than a bit more power and raised EGT. So, at let's say 85 to 90 % throttle, I could maintain about 60MPH and not exceed 850F to 900F, but at 100 % throttle, as speed slowed down to say 65 MPH, near the tops of the hills, EGT would rise towards 1050 (I never let it go above 1050, into the yellow on the EGT). Before the engine was rebuilt, it was stock; it had issues so was likely not the full original 175HP. Yet the truck when loaded as light as it was on this trip would still have no problem on the hills. I would often tow a boat (double axle trailer, net ~5K); now the truck feels almost like it is towing that trailer even when it is not; not quite that bad, but almost. Does this give an idea? Happy to provide more detail if it helps. Cheers

I recall pulling our trailer up some steep hills in the backwoods at 60 at 10psi and I would be around 1000F as well. I cleaned the turbo and set my valves really tight and then I could run high boost lower in the RPM so I could go up the same hill at 8-900F. The fact that you are floored with no black smoke though..if that AFC is out of the way which it should be, then it should be puking smoke. Definitely need to do some testing with that AFC/Fuel Plate/Overflow Valve setup. I kinda doubt the wastegate just because they usually get stuck closed since the amount of time they are open is maybe 1% of the time and the rest they got a lot of tension holding them shut. Timing could also be a factor but not where it has no fuel, it would smoke or something so I'm leaning away from that. Problem with all these issues is not knowing your truck so you just have to check everything yourself and narrow it down until we find something we can work with and pinpoint as being the problem.

I will get a new seal so I can put my dial indicator in (replace the fuel delivery valve after I take it out) and check the timing, check carefully for leaks in the inter cooler, make sure the waste gate is not stuck (even though i suspect you are correct about it more likely being stuck closed than open), and look and see what the adjustment of my fuel plate is and then let you know, OK? might take a day or so. Really appreciate your help, having the opportunity to talk to someone who knows these engine as I am fairly new to them. Worst case, i can try to find someone good in the SF Bay area who has a dyno and knows these engines, but I would prefer to go as far as I can using this approach as I am learning as I go. So thanks again, and I will be back in a day or so. Cheers,

Yeah dig around on that thing and see what you can find. These are very simple engines once you play with them enough. These are all articles about stuff on the pump that might teach you some things.

Well, finally got all the components together to check the fuel pressure. Of course, what I am seeing is not entirely clear as it depends a lot on the setting of the needle valve. If I have the needle valve mostly closed so that the gauge needle dances only a bit, the pressure is about 15psi at idle and drops when I raise the throttle at all. If I open the valve more, the needle in the gauge dances more, ticks louder, but shows about 25 at idle and seems to not drop; it all seems to depend on how far I open the needle valve. According to the pump re-builder, the needle valve was replaced (they are sending another one anyway). This was my first step so I haven't done the others yet, but thought I would pass it along.

The needle valve serves as a baffle sorta by averaging the peaks of the pressure spikes and giving you a pressure. This means you would close the needle valve and open it only enough to get a reading, though on a 12V you can see the pressure pulses without damaging anything (at idle anyways) so you can keep opening the valve until you see the pressure spikes, then back down until it stops bouncing.

The overflow valve goes back to the tank and after it gets past the engine it turns into a rubber line. When you are idling you can slightly clamp that rubber hose and see if the pressure goes up, if it does then the problem is the overflow, if it doesn't then the problem is the lift pump. Don't clamp that line shut or the lift pump will build pressure until something gives..you just want to restrict that line, not clamp it shut. Here are fuel pressure specs. If you were getting an accurate reading, the fuel pressure is a lot less than what it needs to be.

Hmmm, if I go with only a slightly open valve so needle is barely bouncing (like what I see on the gauge on your video), my fuel pressure is too low and stays low, even goes down when I bring RPMs up. If I go with a more lively needle, fuel pressure is around 25 and stays there, give or take a few LBS. The delivery pump is almost brand new as are filters (primary on rail of truck and secondary on engine). No difference between front or rear tanks, plus I have had pick up out of front tank and screen is clean. My return line only goes as far as delivery pump where it tees in to supply. I don't like this because it may cause a hot fuel issue. In any case, slightly squeezing line appears to make no difference. The first time I tried it, I thought it did make a difference, but now it doesn't; this I do not understand unless I over squeezed it and damaged something (pressure never went above 30, assuming gauge was reading pressure correctly). I rechecked timing and it is 19.5 BTDC. This setting was based on 215HP, CPL 2175 to 2023 (no tag on timing cover, non stock engine). Trying to find out from the engine re-builder if these are the values I should be using, but no luck yet. They were best guess of pump re-builder. I don't seen to have an inter-cooler leak. Could be defective delivery pump, even though new? BTW, there are electric fuel pumps in tank which are working (turn ignition key on and they can be heard plus with any opening in the line, fuel shoots out). They have been there since the conversion and have never hampered performance. They are a nice feature as they keep a positive pressure through the system right up to Cummins delivery pump. I perhaps should try taking a fuel line from a 5 gallon bucket direct to delivery pump and be sure there is no issue with tank and line set up (see if pressure improves).

Sounds like the overflow valve valve is ahead of the lift pump based on what you said. This means there is no pressure regulation. The overflow valve needs to have an unobstructed flow back to the tank, it can't be running back into an already pressurized line because it just forms a closed loop and the excess pressure has nowhere to go. Correct me if I am wrong here but I think that's how it is set up? I think raising it to where it is dancing more but has more pressure is only because you are seeing pump pulsation pressure. It is not true pressure. It really needs to be where that needle stops moving. My needle valve wouldn't go down any more in the video (I didn't really use a needle valve but something almost half as good..) so I couldn't make it perfect. Everything else sounds good or isn't far enough off to cause this issue.

The overflow line tees in with the supply lines coming from the tank. You are correct that they are all ready pressurized (by the pumps in the tank but not by the Cummins engine mounted pump), but I believe only to maybe ~ 4lbs or so; I would need to check. In any case, the returns definitely do not have an unobstructed flow back to tank so that is likely a good point. On the other hand, this set up did work fine for about 30K miles before all of this started with the rebuilding of everything (engine, injection pump, etc.). In any case, I will try the test with the lift pump drawing from and the bypass discharging into an open container and see what happens. Many thanks once again