D24T.com  

Go Back   D24T.com > Technical Discussion Area > Diesel Engine and Drivetrain

Reply
 
Thread Tools Display Modes
  #1  
Old 10-19-2021, 12:51 AM
Aiden Aiden is offline
Junior Member
 
Join Date: Jan 2021
Location: UK
Vehicle: D24TDi
Posts: 2
Default Lost power

Hello,
I have a D24TIC, which was rebuilt last year after a blown headgasket and hydrolock. The mechanic claimed the engine was restored to near-factory condition, and it has ran perfectly for the 10k miles since.
On a road trip to europe I got the chance to take it out on the Autobahn where it topped out at around 100mph - not the 115 claimed from factory (although did hit this on a downhill stretch). The 0-60 is also a fair bit longer than what it should be.
Any ideas what could be causing the lost horses? Given that:
The injectors wern't changed during the rebuild to save money as "they looked ok".
The muffler looks like it was salvaged from a shipwreck.
The turbo may be original (250k miles) but can't be sure.
Burns around 1-2L oil between changes (7.5k miles)
All filters etc are well maintained.
Very occasionally get a sudden loss of power (boost) under full load.
Thanks
Reply With Quote
  #2  
Old 10-19-2021, 11:41 AM
ngoma ngoma is offline
Supporting Member
 
Join Date: Nov 2009
Posts: 1,351
Default

Welcome to the forum!

Hard to tell from a distance the exact culprits of your lack of top end power.

I am guessing that you are perceiving a marked difference in performance and top end speed pre- and post- head gasket replacement work, correct? (Or did this just happen more recently? You mention it has worked perfectly for 10k miles, so maybe not?)

0-60 what should it be and what did you measure?

Injectors: given that they were not changed, we can rule them out as contributing to the difference in performance before/after.

Muffler appearance shouldn't matter unless it is clogged or incorrectly sized. Why was it changed for a HG R/R?

Turbo: Can you attach a boost gauge to help monitor what it is doing?

That amount of oil use is not bad.

Sudden loss of power (boost) under full load: Momentary or sustained? High RPMs, or low RPMs? Does it let out big puffs of smoke when this happens?

These are all questions to help us match up the symptoms to known culprits.

PS: These engines have suffered greatly at the hands of (otherwise good) mechanics not experienced with the specific idiosyncronicities of this engine. What about your mechanic and his/her track record with these engines?
__________________
1985 744 gle d24t
1985 745 gle d24t
Reply With Quote
  #3  
Old 10-19-2021, 10:57 PM
v8volvo v8volvo is offline
Supporting Member
 
Join Date: Jun 2009
Location: Montana, USA
Vehicle: '86 745, '83 764
Posts: 1,618
Default

One other question occurring to me to add to ngoma's list above -- does your engine have EGR?

The EGR system (when present) on these D24T/IC is a very early design that uses stone-age controls relying on a half-dozen components that all can fail and have zero ability to self-diagnose. These include some electrical and vacuum switches around the throttle lever, a few solenoids and control units, a thermal vacuum switch etc. All very unsophisticated and vulnerable to failure in old age, and unable to alert you to any issues.

If your engine has this EGR system, then it might benefit your diagnostic process to temporarily or permanently disable it and see if that changes or eliminates the intermittent power loss you notice. If one of those switches or solenoids does the wrong thing at the wrong time and the EGR valve gets commanded open while you are running at full load, it could cause what you have been feeling. In fact it is hard to imagine much else that could cause a momentary power loss like this on an otherwise simple mechanically controlled engine.

The EGR equipped engines ALSO have the tendency to constrict the intake manifold passages since the carbon soot from the EGR can mix with oil vapors from the crankcase vent return, forming a cokelike hard substance that adheres to the walls of the intake runners like heart disease. Not commonly known to be a performance issue on D24T/IC engines, more just a mess, but then again, most of us have not been able to test the top end performance of our engines like you have. If this were present and restricting airflow, you would notice it most in a situation of high speed operation. Probably wouldn't notice it at all in short bursts of low speed acceleration.

Search images of "TDI clogged intake manifold" for an illustration of the worst-case for how this can look, although again D24 type engine doesn't do it as badly as those do.

If you don't have EGR then of course all of this is irrelevant to your situation.
__________________
86 745 D24T/ZF 345k lifted 2.5"
83 764 D24T/M46 155k
Reply With Quote
  #4  
Old 10-20-2021, 12:21 PM
Aiden Aiden is offline
Junior Member
 
Join Date: Jan 2021
Location: UK
Vehicle: D24TDi
Posts: 2
Default

Thanks for your help,
The engine had head gasket problems since I bought it last year but the performance seems fairly similar before and after the rebuild. The exhaust system wasn't changed, just thought I'd mention that it looks very rusty on the outside and so may be clogged?

The loss of power under loads has only happened 2 or 3 times and seems to be something like a wastegate opening or perhaps the egr because it only lasts for a few seconds and is at full boost (+3k rpm).

I have the egr switched off electronically using the idle cut-off switch wired into a new switch in the cabin (for emissions tests/city driving), but may replace the blanking plate since I doubt it has much effect.
I recently cleaned out the intake manifold, and have only ran the egr for a few hours since, so that should be fine.

I went with an experienced mechanic who worked on the engines a decade or so ago, but I think much of the work was done by a colleague without any experience with the platform. I also gave him the green book for the N/A D24 for reference so he may have timed it incorrectly if there are differences with the turbo engines.

With the engine running as well as it is (+40 mpg on a run) I would guess that it's either a tired turbo or something that would only limit to end performance (3 notch gasket?).
Hope this helps.

Last edited by Aiden; 10-20-2021 at 12:23 PM. Reason: Formatting
Reply With Quote
  #5  
Old 10-21-2021, 11:25 AM
ngoma ngoma is offline
Supporting Member
 
Join Date: Nov 2009
Posts: 1,351
Default

Quote:
Originally Posted by Aiden View Post
...I would guess that it's either a tired turbo or something that would only limit to end performance (3 notch gasket?).
Going with your guesses, It's easy to verify.

Easy to splice in a boost gauge into the tubing that runs from the intake manifold to the IP LDA. Boost under load should start developing around 2000 RPM and reach full boost 10-11 PSI at full load 3000 RPM.

Head gasket notches or holes can easily be seen at the gasket portion that extends out, under the upper radiator hose flange. However, even if you find a 3-notcher, you can't really be sure it is actually too thick unless you measure the piston protrusion from the deck. Ask your mechanic if they did in fact to this, as opposed to just grabbing the (more easily obtainable) 3-notcher.
__________________
1985 744 gle d24t
1985 745 gle d24t
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -8. The time now is 05:58 PM.


Powered by vBulletin® Version 3.8.10
Copyright ©2000 - 2024, vBulletin Solutions, Inc.