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Discussion Starter #1
Hi there. This is my first post. I have just acquired a 2002 e450 7.3 with 300,000 km. Everything works fine, no smoke, no error codes, starts without issues.
I'm suspicious of the turbo since this is a retired ambulance. I put my obd2 monitor on and using the torque app app with the Ford PIDS, I found that at WOT my maximum boost (MAP) was 9.2 psi with a drive pressure (EBP) of 26.8 psi.
I understand that the drive to boost ratio for van turbos is 1.15:1. So at 26.8 psi drive pressure I should be seeing 23.3 psi boost (26.8/1.15). Since I'm only getting 9.2 psi I'm concluding that my turbo needs to be rebuilt. Is my math correct? There is no Wastegate in vans so intercooler air leaks are not an issue.
Is this the correct way to diagnose my turbo using sensor readings and in lieu of obvious indicators (smoke and or loss of power)?
I'm looking forward to being impressed by your collective wisdom.
Thanks!


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Don't Trust the Sensors! What are the KOEO numbers on the MAP and EBP sensors? First thing I'd do is wander down to a hardware store and buy a couple of Tee's and some fittings, 1/8 inch poly tubing and a pair 0-30 psi mechanical gauges. Find the MAP hose and Tee into that with one gauge, then find the EBP sensor and Tee into that with a second gauge. Go out and retest while watching the gauges. You could also pop the turbo intake off and push/pull on the compressor wheel nut to check for axial shaft play.
 

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Project Shamu
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Boost : Drive ratio is not determined by the exhaust housing (if thats where you are getting the 1.15 from). Stock turbos in all 7.3 platforms are very inefficient, and are closer to 1.8:1-2:1.

Also, make sure your EBP rating isnt including atmospheric pressure. (roughly 14psi at sea level). If it includes atmo, then instead of 26.8, its really 12.8 (varying based on your altitude). Which is pretty close to what you are seeing boost wise.

Also, you cannot tee into the EBP sensor, its a hard line.(atleast not easily).

Turbo wear can be indicated based on shaft play (like cjfisher said). In/out I dont find as important, and even new turbos have some play in/out. But the up/down, which is bearing play, is what I always look for.
 

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Lt.Dan - I was thinking that you could Tee into the end of the tube. IE unthread the sensor, put the Tee in and then reconnect the EBP to the Tee.
 

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Discussion Starter #5
Thank you for the quick responses. You guys are great.
The MAP number is with atmospheric pressure removed (at least that is what the PID formula says). The 1.15:1 (drive: boost ratio) is specific to the van turbo. It's different from truck turbos because it doesn't have an intercooler. My question remains, however, assuming the sensor data is correct, does a discrepancy between actual boost and expected boost based on exhaust pressure indicate a bad turbo?
I will open her up and check for play (axial and in and out) and report back.
Thanks again.
 

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Nascenta,

Your EBP number sounds very much like exhaust + atmospheric pressure. I drive a 97 F350 with no intercooler (well yet) and my numbers are similar to what you have once you subtract atmospheric pressure. I use FORScan to read the PIDs off my truck and both EBP and MAP are in absolute. Perhaps I'm not polling the correct PID, but I have noticed and read that our 7.3 engines do not have a standard implementation of the OBD protocol, it is really a "heavy duty diesel" protocol that is pushed through the OBD comm line (which is why ordinary OBD readers can't read our trucks). WOT with 19.5k behind my truck I can only get up to around 11 psi (mechanical gauge in cab) of boost. I also have a mechanical gauge plumbed in pre-turbo (unfortunately I can't remember the exhaust pressure when I pulled 19.5k). However, on a typical drive home (truck is also my commuter) climbing some light hills I'll see 4 to 5 psi of boost with 6 to 8 psi of exhaust pressure.

One other thought that occurred to me as I have been typing... Does your van still have a EPV (exhaust pressure valve)? On the older 7.3s these valves are used to help the engine warm up in cold weather (and to prevent wet stacking). They can get stuck in the closed position which will increase the exhaust pressure. I have seen my EPV drive the pressure up to as much as 25 psi on my mechanical gauge during the cold months. If you have an EPV, it could be that it is stuck in the closed position. When this happens the truck tends to run like a slug - it will feel like the truck is not making power.

Edit: I haven't really answered your question... I know from Lt.Dan's postings that when his turbo was going starting to die, the turbo would gradually make less and less boost when given the same throttle and load. When he got into his turbo he found a fair bit of axial endplay and some runout (side to side or concentricity). So.. YES a discrepancy between actual verses expected boost could be an indicator that the turbo is on its way out.

Cj
 

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Project Shamu
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Thank you for the quick responses. You guys are great.
The MAP number is with atmospheric pressure removed (at least that is what the PID formula says). The 1.15:1 (drive: boost ratio) is specific to the van turbo. It's different from truck turbos because it doesn't have an intercooler. My question remains, however, assuming the sensor data is correct, does a discrepancy between actual boost and expected boost based on exhaust pressure indicate a bad turbo?
I will open her up and check for play (axial and in and out) and report back.
Thanks again.
I can guarantee the turbo is not making 1.15:1 boost:drive pressure. Van turbo, truck turbo, OBS, E99, L99 it doesnt matter, they all work off the same platform and are NOT that efficient. If they were, people would be running big injectors with stock turbos all the time.

12-15psi in a non-tuned truck (or van) is normal under heavy load conditions, any less would indicate a leak (on either the intake or exhaust side), a poor running engine not creating enough back pressure (like worn injectors or worn HPOP), or a worn out turbo.

Check for shaft play in the turbo.
 

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Discussion Starter #8
I've checked turbo for play and it seemed tight axially (no wobble) and in and out. There is a little wear on the fins because the unit has been pushed out and has been rubbing slightly on the housing as can be seen in the photo. I suppose I could have knocked on it and pushed it back in to it's original position but I didn't want to risk wrecking it. I also took a video of it spinning. I wonder if I can post that. Anyway, it seems good. Hardly any oil.


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