HOW-TO: Rebuild Diesel IDI Injectors

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Sat, 29 May 2010 13:14:27 +0100

Vince, excellent site. thank you so much for providing this resource to the community! do you know of a source for shims to adjust these guys? thanks again! -bob Hi Bob... thanks for your comments! Unfortunately I don't know of a reliable source for a "kit" of shims... VW will sell you them one by one of course. I got my stash during a group buy on a VW forum... some kind soul bought a ton of each size and then made individual kits with 5 each... but I've not seen that offer repeated anywhere else since. Sorry I couldn't help more, Vince - Bob

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Mon, 21 Dec 2009 18:48:03 +0100

Great page, I have just replaced the injectors on my 84 1.6d jetta and I can't get two of the injectors to stop blowing exhaust out through the injector holes. I have spent close to an hour on each injector hole cleaning every last spec of carbon build up out of them before I put new heat shields in but I can't seam to get them to seal properly, and I have even stepped up the torquing to 54 ft-lbs and then max 56 ft-lbs. I have bought complete reman bosch injectors including the housing so I'm not sure if this could have anything to do with it but I have never had this problem before when I have done compression tests on the engine. I am about ready to pull the last hair out of my head. If you have any suggestions that would help that would be really appreciated. Thanks, Brendan - Brendan

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Tue, 01 Sep 2009 22:06:02 +0100

Just wanted to say sweet site, I never even thought of rebuilding an injector, now I feel stupid. Thanks for the education, this is great stuff. Thanks so much for sharring - Duffy

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Fri, 24 Jul 2009 14:17:45 +0100

hi i wonder if you can help me i recently bought a set of injectors for my 2.3 tdi frontera (bosch)and noticed that a little diesel was leaking out between the top and bottom half so i removed them (2) and tightened them up (vice and 22mm spanner as they were new it wasnt too bad) will this affect the injectors in any way (the opening pressures of the jet especially as they were factory set) this is probably a stupid question but i am new to diesel and i am learning as i go if you could answer this i would be very thankfull to you many thanks Karl - karl

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Thu, 11 Jun 2009 03:08:20 +0100

dig your write up! in order to equalize pressures to ensure even sanding hand lapping is best done in a figure 8 pattern! - john

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Tue, 12 May 2009 02:03:37 +0100

Vince, Do you happen to know if 1.6 or 1.9 injectors would be better on a Frankenstein engine? I am building a 1.6 mech block that I am fitting a ported 1.9 hydro head to. I will be running the 1.6 turbo/manifolds(port matched) and injector pump. The 1.9 injectors are probably fresher and I wondered if the dual stage would be any benefit and would work ok with the 1.6 pump? Thanks, Barry. - Barry

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Sat, 09 May 2009 15:34:16 +0100

Do you have any resources or links to sites that are familiar with the AAZ two stage injectors. I am having difficulty in finding someone who knows how to set both stages. Thanks - Scott

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Thu, 16 Oct 2008 09:59:28 +0100

Does increasing the pressure of the injector effect the spray pattern? for better or worse? I just wondered if increasing the pressure would improve atomisation and mpg... My experience is that for standard diesel there's not much change in the spray pattern between 130 bar and 155 bar. Up around 180 I would say the cone is more defined and less "foggy"... probably not in a good way. Some people that run bio fuels seem to favour higher breaking pressures so ensure better atomization... I have no experience myself but it makes sense to me. There are some theories that pump losses start to become a factor over 160 bar, and I've read a couple of places that the sweet spot for mileage seems to be 140 bar... because I run pretty high boost (20+ psi) I've stuck with the stock 150. The main thing to keep in mind as you experiment is that the breaking pressure and static pump timing are directly related, so if you play with higher breaking pressures you'll need to ease off on the pump timing a bit to compensate. Vince - ClintJ

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Sun, 07 Sep 2008 14:46:56 +0100

Hi,great site,by the way....my question : can we use same injectors in a AAZ without the turbo? I rebuilding a 1,9 NA without the turbo and worry about leaving the same injectors. Can I use the old injectors from the 1,6 NA ? Just my opinion... but I don't think the actual nozzles are all that specific. More important is that they are working properly and with a consistent breaking pressure. So, I'd go ahead and keep your same injectors with or without the turbo... just make sure that they are spraying properly. BTW... the AAZ injector bodies are quite a bit taller than the 1.6 injectors, so if you were to switch to the 1.6 injectors you'd need to round up a set of matching 1.6 hardlines. Vince - cyrille

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Sun, 31 Aug 2008 10:04:58 +0100

Hello Well layed out and informative. Just a comment to Pete, I wonder if someone has "PLAYED" with the pump delivery screw.I have seen this a number of times. Gives more power, more smoke, and decreases fuel economy. Bought a 1992 that was played with that smoked so bad you couldn't see behind you on a hill. Turned the screw out a total of 2 1/2 turns. Runs real well and no smoke. Allan - Allan Daem

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Fri, 15 Aug 2008 14:38:21 +0100

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Fri, 15 Aug 2008 13:53:16 +0100

Is it normal for the pressure to "bleed down" at a visible pace on the gauge if you pause in pumping, or do I just have a leaking seal somewhere? I finally build pressure, now it leaks down (though if I pump quickly enough, I get a very nice injection from the fresh nozzle... at 163 bar for the first shim I tried! :o We'll tap that down a notch, Mmm? -Kurt a.k.a Turbinepowered :D Hi Kurt... the bleed-down could come from a couple of places: the injector itself or the valve in your pressure tester. If you're seeing it on every injector you test I'd suspect the tester itself... if you have an old injector body you could build a plugged body with JB Weld and see. Vince - Kurt

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Thu, 03 Jul 2008 06:36:58 +0100

Thank you. It worked out great. Ralph Wheatfield, IN - Ralph Suges

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Thu, 26 Jun 2008 05:21:20 +0100

Hey Vince, not the MB-Nozzles are the favoured ones, the VW-AAZ nozzles DNO SD297 are the best vor IDI and DI VWengines, also for turbo and non-turboengines best results Tom Hi Tom.. thanks for your comments. Yeah I've certainly been hearing mixed results lately about the Mercedes nozzles... would be really nice to dig up a definitive chart that gives the flow specs etc for the various Bosch nozzles but so far no one seems to have that info... maybe some day !!! Vince - tom

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Fri, 23 May 2008 09:44:20 +0100

thanks for the info, I am new to VW diesel mechanics, i have a 94 Jetta with a 1.9 aaz. the reason for the new injectors is that when I am drivin on the highway and give it good amount of throotle i get black smoke. i installed a boost gauge and on the highway its about 8psi max, but spools very quickly. and ideas how to make it smoke free? Hi Pete... Good for you for trying to figure this out... many people think that "diesels just smoke" and it's too bad because it's one thing that gives them a bad rap... a diesel in proper tune should be pretty much smoke free *except* for a bit of white-blue smoke first thing cold winter mornings and perhaps a bit of black haze under full power. Black smoke means your engine has is getting more fuel than it has time to burn. It also means your EGT temperatures are higher than then need to be. My first recommendation is always to start with the basics: timing. Make sure both your cam and injection timing are bang on... somewhere in the 0.95 mm range for an AAZ seems to be the sweet spot but you can move to 1.00mm if the engine doesn't seem too noisy. Second is injectors: how many miles have they got on them ?? If more than say 100K it's time to have the nozzles replaced and the breaking pressure calibrated. A local diesel shop should be able to pop-test them and recalibrate if you're not sure how old they are. Third is airflow: adding more air will help the fuel burn better and reduce EGTs. Is your air filter in good shape ?? 8 psi is probably on the low side of normal for an AAZ turbo... you could try dialing up the boost a bit (screw with a locknut on the wastegate)... a couple of psi might reduce the smoke and add a bit more performance. Best of luck... let us know what you find out !! Vince - pete Skrabek

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Thu, 22 May 2008 07:59:33 +0100

Hey Vince what a great page, just wonderin, what is the stock breakin pressure on 1.9 aaz injectors. I got a new set of injectors with merc 300d nozzles that are set to 155 bar. Just wonderin what my stock settings are. And if these injectors are the 1.6 design (single spring) maybe I would be better off putting the merc nozzles on my AAZ injectors(2 stage). Thoughts? Hi Pete... Stock breaking pressure for AAZ dual-stage injectors is 150 bar. I've got a set of Merc nozzles but have not had time to put them in my AAZ yet so can't really comment. I've actually gravitated more towards the "stock nozzles are fine for all but the most extreme performance needs... it's all in the pump" point of view and am getting very good performance out of my stock AAZ nozzles. Someday I will play, but when I do I will likely switch my AAZ over to single spring injectors... much easier to calibrate, if "playing" is my objective. Vince - pete Skrabek

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Thu, 13 Mar 2008 09:43:40 +0100

Vince, this page is a great resource...well done! I have a question though. When adjusting the pop pressure on these injectors, I assume you change out the washer above the spring. Where can you get thicker washers from? Thanks. - Andy

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Tue, 12 Feb 2008 12:54:12 +0100

Cool pop tester. It appears to be based on a bottle jack. Did you buy or make this? Hi Neil... yup it's home-built.. a 20 dollar bottle jack and a 10 dollar gauge plus a little welding. OK, so I soon upgraded the gauge to a 30 dollar one but still a bargain considering that they can be 10X that on eBay, and it's a pretty important step in the process. I'm amazed how often I actually use it... lots of diesels in the neighborhood I guess ! Vince - Neil

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Tue, 15 Jan 2008 17:30:18 +0100

Great page Vincent, I threw in a good word for you at the forum site: http://www.vwdieselparts.com/forum/ Do you know how to make an injector tester? - Bert Carrier

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Fri, 23 Nov 2007 18:48:08 +0100

I think it depends on what you are after. In general, if the injectors were accurately calibrated in the past, and if you keep all the parts from each injector together in a group as you are rebuilding them they should stay fairly close to each other overall. However, the lapping process tends to remove a bit of metal and so I've noticed that my nozzles are usually 10-20 bar over their normal pressure after lapping... so I'd say pop testing is probably important. I personally want to make sure that they are all as close as possible... another reason calibration is an important step. And, I hate discovering leaks on the engine... much nicer to discover them on the pop tester !! - vince w