VW TDI forum, Audi, Porsche, and Chevy Cruze Diesel forum banner

1 - 5 of 5 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #1
I have a 1998 Jetta TDI.

My #1 injector is running zero at idle, lean at half throttle and then rich after that. My mechanic switched out that injector with another one and it is doing the same thing.

This problem came up after I replaced head, although it may be unrelated. My mechanic says that should not make any difference.

Someone suggested the pressures are not balanced, if that is the case could someone please explain how to diagnose and fix this.

I have been using Stanadyn additive religiously.

Thanks in advance.

John
 

·
Premium Member
Joined
·
23,902 Posts
Moved to mk3 forum since a 1998 jetta TDI is a mk3.

"The pressures are not balanced" sounds like a good solution but if your mechanic switched it out and there was no change then the problem is not in the injectors. When you say "it is doing the same thing" do you mean the problem is following the injector or it still stays on #1 cylinder? This will isolate the problem to either the injector or cylinder. The most likely cause is a sticking nozzle or some internal problem to the injector.

Is it getting fuel? Slightly crack open the fuel hard metal lines going from the injection pump to the injector. Wrap it with a thick rag. Do not use your hand or a thin paper towel. Crank the engine over and fuel should come out. Maybe the fuel filter is clogged and causing fuel starvation.

Any error codes? Any wiring shorts going to the injection pump? These cars are getting old and in the process of replacing the head a ground wire or other wire could have gotten bent/damaged.

If it's running zero at idle it would cause the engine to shake a lot. I do not believe that it is because you replaced the head. The obvious cause is a faulty injector but your mechanic switched them and said #1 was still shaking it suggests another problem. Maybe the metal fuel line got bent? You really cannot unbend them since there will be a fold in the line. Either that or the injection pump is faulty.
 

·
Registered
Joined
·
51 Posts
2nd, sounds like a fueling problem at the injector or fuel line. It's pretty rare for an IP to fail on only one cylinder.
 

·
Registered
Joined
·
2 Posts
Discussion Starter #4
This is what my mechanic is thinking, any additional insight would be greatly appreciated.


I'm leaning toward a control (pump,ECM, adaptation?) issue since the substituted injector is producing the same results as your original injector. If it's a delivery (injector) issue then the presumption is that injector #s 2,3,4 have all failed in the same way and the probability of that is unlikely.

I think the big question is how does the ECM come up with the mg/stroke figure that is displayed on the laptop. Is it the amount of fuel that is being requested? Or is it the actual amount of fuel that is being delivered? Requested fuel may be adjustable thru the ECM adaptations. Delivered fuel is probably related to the pump or the pop off valve for #1.

On boost they give you both, requested & delivered so you can fine tune the wastegate.
 

·
Premium Member
Joined
·
23,902 Posts
I believe that it's metered at the injection pump and this is what it is reading. After it leaves the injection pump it does not directly know how much fuel is at the nozzles or in the return lines. The sensor on the #3 injector is the nozzle lift sensor and it detects lift and duration of the injection.

It indirectly knows how much fuel there is by engine rpm and load, throttle position, air flow, etc. So to answer your question it's the actual amount of fuel leaving the injection pump. This is not necessarily the amount of fuel being injected into the engine. On the boost sensor there is a sensor that reads boost.
 
1 - 5 of 5 Posts
Top