7020 boost pressure
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=190261
Printed Date: 07 May 2025 at 4:21pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: 7020 boost pressure
Posted By: cowkicker
Subject: 7020 boost pressure
Date Posted: 23 Aug 2022 at 9:01pm
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Was wondering what the manifold pressure should be on a 7020. I have a 7020 that runs and sounds great but lacks for power. Today I put a cheapo, hard to read gauge on it and at idle it was about 8 lbs, at wide open throttle on level ground it was 10 lbs when starting uphill it would run up to about 12-13 lbs then fall very fast with tractor choking down. Have to down shift to 5th then to 4th just to get over moderate hill. Turbo feels good, air filter clean, new fuel filter, pump and injectors rebuilt, good compression. I got this tractor a few years ago from neighbor who said it just didn't have any power, I figured it was just like normal 7020s trying to turn the big pst, but this is worse than any 7020 I have ever driven. Any suggestions? Thanks
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Replies:
Posted By: DrAllis
Date Posted: 23 Aug 2022 at 9:52pm
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At an idle the "boost" (taken at the intake manifold) will be ZERO !! So, why do you say you have 8 lbs of intake turbo boost ?? Maximum boost under full load at 2300 RPM's (with the hand throttle wide open) should be in the 20 to maybe 22 psi range. Your's falling off is an indication of fuel starvation as you describe it and/or a bad air leak like a blown intake gasket. True turbo intake boost cannot be 8 psi at an idle. Take the muffler off and try it again.
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Posted By: cowkicker
Date Posted: 23 Aug 2022 at 11:38pm
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Removing muffler made no difference, lower part of gauge didnt have numbers just had a black line til needle reached 10lbs. really didnt pay attention where needle was when tracor was not running, a true zero. Will check that sometime. Lots of black smoke when dying down. Just had enough hose to barely reach inside door, hard to hold it and drive, throttle, watch gauge, ect. Will get longer hose, better gauge sometime a let you know. Would starting fluid sprayed around intake change sound or speed up engine if it was leaking?
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Posted By: DrAllis
Date Posted: 24 Aug 2022 at 6:33am
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I would think starting fluid all around the intake manifold where it bolts to the cylinder head would be a good check, yes. Anywhere between the turbo and intake while idling.
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Posted By: MACK
Date Posted: 24 Aug 2022 at 6:49am
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Normal boost would be 1 LB of boost for every 10 HP. Sounds like you need a new gauge. At a low idle, with no boost, spraying starting fluid around manifold with a leak should make it knock. Sounds like you may have a blockage from air intake to turbo or fuel restriction. MACK
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Posted By: Charlie175
Date Posted: 24 Aug 2022 at 7:32am
Used a 6080 that would die off under load. Changed filters and still no go. Drained tank and the inlet was partially clogged (Chicken litter environment). Ran great after cleaning it out.
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Charlie
'48 B, '51 CA, '56 WD45 '61 D17, '63 D12, '65 D10 , '68 One-Ninety XTD
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Posted By: DrAllis
Date Posted: 24 Aug 2022 at 7:45am
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Using a 100 lb gauge doesn't work for this. A 30 psi gauge is best. A healthy 7020 is 20 psi boost or more under full load. A 7040 is closer to 14 psi boost under full load. The smaller engine has to run more boost to make 123 rated HP.
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Posted By: jeickman01
Date Posted: 25 Aug 2022 at 8:16am
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Wouldn't "a lot of black smoke when dying" indicate that the problem is not fuel delivery but, instead, air? Also, I've never tried the starting fluid trick so I have to ask - is there enough intake manifold vacuum in a turboed engine to draw this in through a leak?
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Posted By: tbran
Date Posted: 25 Aug 2022 at 10:32pm
A fuel restriction will retard the timing and cause black smoke.. The first think we do in a low hp is eliminate the tractors fuel system - We have a 2.5 gallon jug with clean fuel and run it straight unto the rear of the fuel pump - 90% of the time it runs great this way - then one has to start back tracking the fuel system to check for air leak and obstructions. Usual places to look are the fittings and check valves on the hand pump if so equipped, air ingestion on the electric pumps if it has one, the bottom hole on the fuel filter base and any place there is an elbow.
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When told "it's not the money,it's the principle", remember, it's always the money..
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Posted By: New Allis Guy
Date Posted: 26 Aug 2022 at 3:06pm
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Is this a Roosamaster pump? If so, a partially clogged return check valve can cause what you're describing. I've had it happen on a couple tractors until they eventually wouldn't run at all. I've never had a 7020 though, so maybe it has a different pump
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