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Discussion Starter · #1 ·
Hi all,

Has anyone else known a similar problem, or can point me in the right direction? My 3.0 TD '99 Trooper will sometimes run rough when cold, sometimes perfect when cold, and always perfect once fully warmed up. When it runs rough it 'dies' down to about 400rpm, then instantly jumps backup to approx 700rpm about once per second, over and over - very annoying.

Cheers.
 

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Given that there are only a handful of diesel Trooper owners in the forums, you may not get an Isuzu-specific answer. I'll answer with the normal diesel troubleshooting information:

Glow plugs. Make sure that they are all healthy. This is usually done by disconnecting them and either testing each one with 12V or by checking the resistance of each one. If you remove them it is a good idea to gently clean the holes with a wire brush or drill bit (small enough to not remove any metal, large enough to clear carbon from the holes).

Compression. A diesel needs good compression to run. When cold diesels that have poor compression tend to be harder to start. If you have valves that need to be manually adjusted, it might be time to adjust them.

Injectors. If your injectors have caked up they may not be spraying very well. This can be a blockage that causes a poor spray pattern, or an injector that doesn't close all the way. Using a product like Diesel Purge or having the injectors professionally cleaned can help a marginal injector.

Because all 3 of those items can cause problems with a cold engine you should see what makes sense to do/check on your engine. As a general maintenance item on a diesel, replace the fuel filter(s). You should check the air filter and replace it if you can't remember the last time it was changed.

Good luck and be sure to let us know what works.

-Tad
 

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My 2.8 diesel always runs rough when cold - the colder, the rougher - it's par for the course.

My Bighorn is a 2.8 which comes with a manual idle lock on the dash board - not sure if the newer ones did. You start the truck, step on the gas until the idle is smooth (usuall about 900rpms) and then tighten the idle lock.

When the truck is warm, you loosen off the idle lock and all's well...

But for a diesel, I wouldn't worry at all about rough idle....unless it's accompanied by bad noises and poor performance.

BH

PS: Tad correct me if I'm wrong but glow plugs only affect starting, not running, so will have no effect on idle once the engine has been started.
 

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Glow plugs will effect idle in the sense that if one has failed that cylinder may not fire at all until it heats up enough from the others running to fire. Some diesels also run the glow plugs after the truck starts (and after the glow plug light goes out) to smooth out the idle by warming the head up faster than it would be warmed by just idling.

-Tad
 

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Discussion Starter · #5 ·
Thanks for the replies. I have done all the regular service (oil, filters etc). I posted the same question on a UK site - www.itocuk.co.uk. So far we are down to the oil pressure sensor, or air in the fuel line. Am going to install a clear piece into the fuel return line first, and after that get the sensor checked out.

Cheers.
 
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