Fuel Injector Test

[RSTurboFWD90]

I think my engine ('90 Turbo) bucks because of a fuel problem. It only bucks at cruise. When you step on it there is no problem. My fuel injectors all have proper resistance and you can hear them working. Can they still be causing this? How else should I test them to see if they are good?

 

[1g_tsi_awd]

Have you ever cleaned them?
Possibly getting carbon build up?

 

[RSTurboFWD90]

I've never had them out. I'm guessing from your question that I could seen some sort of crud on them. How would I go about cleaning them? Is there some other test I can do while they are out?

 

[1g_tsi_awd]

You can go to any local auto store (i.e. Autozone, NAPA, Pep boysm, etc...) and you can by injector cleaner, You add it to your gas and it cleans them..

 

[RSTurboFWD90]

Oh. I have done that many times.... from your cleaning question I was thinking you should do more, like take them out and soak 'em. Thanks.

 

[ericmetcalf11]

That is exactally what my friend's 1g did. It ended up being the ecu. Have you checked/replaced the caps yet?

 

[RSTurboFWD90]

I haven't checked the ECU but I did find something else just now. I got my hands on an analog multimeter and discovered that the TPS is "jumpy" from just off idle to about 1/3 throttle. I'm thinking it could be telling the computer that the throttle is moving (jerking)when infact it is not. What do you think? I'm trying to rationalize all this before I replace anything expensive but this seems to fit the symptoms.

What are the symptoms of leaking capacitors?

 

[akdsmer]

A "bucking" at cruise is less likely to be a dirty injector as it is more of a PCM input/Ignition problem.

If you believe it's a dirty injector, you could get a "motorvac" or similiar on-the car cleaning done. It's a much better cleaning, as the solvent is much more potent, thus requiring it to be entered at the fuel rail and not the fuel tank. If you want the injectors correctly cleaned, you will have to remove them and send them out to be ultrasonically cleaned. Numerous places to this service, many in fact keep injectors in stock and can ship them out to you. Not only are they cleaned, but they are flow-tested as well, so you can be assured that they are matched and have a clean spray pattern. www.lindertech.com is one such outfit, and I have personally witnessed them clean many injectors. It is a quality operation and one I'm not scared to recommend. Gas tank style cleaners work very poorly and are more of a maintenance type supplement rather than a remedy.

Your "bucking" could be many other things as well. A quick momentary "buck" is usually associated with an electrical/ignition problem. With a scope it's easy to weed out electrical problems as I would watch both the injectors and the ignition signals and watch to see if either cut out. That can occur with a CAS problem or inputs like TPS, Idle switch, MAF and such.

 

[silvawolfe]

A "bucking" at cruise is less likely to be a dirty injector as it is more of a PCM input/Ignition problem.

If you believe it's a dirty injector, you could get a "motorvac" or similiar on-the car cleaning done. It's a much better cleaning, as the solvent is much more potent, thus requiring it to be entered at the fuel rail and not the fuel tank. If you want the injectors correctly cleaned, you will have to remove them and send them out to be ultrasonically cleaned. Numerous places to this service, many in fact keep injectors in stock and can ship them out to you. Not only are they cleaned, but they are flow-tested as well, so you can be assured that they are matched and have a clean spray pattern. www.lindertech.com is one such outfit, and I have personally witnessed them clean many injectors. It is a quality operation and one I'm not scared to recommend. Gas tank style cleaners work very poorly and are more of a maintenance type supplement rather than a remedy.

Your "bucking" could be many other things as well. A quick momentary "buck" is usually associated with an electrical/ignition problem. With a scope it's easy to weed out electrical problems as I would watch both the injectors and the ignition signals and watch to see if either cut out. That can occur with a CAS problem or inputs like TPS, Idle switch, MAF and such.

2nd that, try checking all your connections especially around the coils, ptu, and the ecm.
If it was an injector you would lose power but it would't buck. If you still think its a injector than pull your cas and with the key in the run position and the coil and fp disconnected turn the shaft on the cas. Your injectors should click as you turn it.

 

[steve]

If your TPS is noisy it's a good place to start. If it gets too noisy the car will start bucking and throw the TPS CEL.

Steve

 

[1990talon]

About the fuel injector cleaner that you ad to your tank, This is not the best idea over time it will cause you problems. Your gas tank has a liner the chemicals over time will eat through the liner. This will cause the crap to go though you system and then you will be replacing you gas tank and flushing the fuel system. I am not saying in any way that if you use fuel injector cleaner once your going to have problems. When you start to have problems is when you use it often like every tank or once a week. It is a much better idea to just run it through the rail and injectors as someone said above it will do a better job and not cause problems. In my opinion from experiance the best way to get them clean would be take them out and have them cleaned. Once agian I am not saying that some injector cleaner in the gas every once in a while will hurt, it is excessive repeted use that dose this.

 

[RSTurboFWD90]

I've ordered a new TPS and will let you know if that was it. I'm also pulling the throttle body to clean it and the ISC. Thanks for all the input. Stayed tuned.

 

[akdsmer]

Before just throwing parts on, you can check the idle switch by simply unplugging it. If your bucking stops, then the idle switch is bad. I've seen a couple of these go bad...

 

[RSTurboFWD90]

Thanks. I already tested the idle switch. It's OK. My new TPS should be here Monday. I'm not going to be able to do the work until after Labor day though. I'll post result then.

 

[RSTurboFWD90]

UPDATE: I'm spent the weekend putting in the new TPS and sadly the car is doing the exact same thing. Darn, I was 99% sure it was the problem. When the engine is not completely warm, it bucks like you are cutting off and on the ignition. It's almost undriveable. When it's completely warm you can drive it but you can feel mild stutter at cruise. If you get into it, it has good boost and runs smoothly. Any ideas why a cool engine behaves this way?

I don't have access to a scope so I'm running out of ways to check things.

This car has new TPS, ISC, PTM, coilpack, fuel filter, plugs and wires. I've tested the EGR and purge system. I have never had a CEL for this problem.

 

[sillyme]

try this and check to see if you have any boost leak. check timing.

 

[RSTurboFWD90]

Timing is good. Why would I be concerned about boost leak? All the problem is just off idle, well before any turbo boost. And like I said... if you get into it, it runs perfectly.

 

[shaunman1979]

Hey RS I was having the exact same problem with my Laser right before it blew a head gasket. ( that was not the cause ) Im doing a complete Tubo swap to a doner body so I have the ECU out. When I get home today Ill check it for corrosion around the "Caps" Thats the only thing I can think it would be. Keep us posted if you find anything I would love to know what is doing this before I put my car back together.

 

[RSTurboFWD90]

Thanks for the post Shaun. I ordered a pocketlogger so maybe I can get some more engine data to help me. Should have gotten one long ago since I'm the original owner and plan to keep it forever. I'm going away next week (for 15 days) so my work on it will be delayed until I get back.

I should also mention that my new ISC makes alot of noise just like the old one. It's a chattering sound when you turn the key to on. You can also hear it when the car is idling if you lay your ear on the intake manifold. Can the ECU be doing this?

 

[shaunman1979]

I have never noticed my ISC making any noise but then again I never had paid to much attention to it. I dont know if the ECU would cause that to be noisey. I thought it was somthing with my fuel system as well. I put that junk in the tank, changed my fuel pump, plugs, wires. After all that It did the same thing. The car would shutter if I was just cruising But if I put my foot into it nothing. It should be a few weeks before the swap will be complete so I look forward to hearing the diagnosis. Good luck with it.

 

[steve]

I should also mention that my new ISC makes alot of noise just like the old one. It's a chattering sound when you turn the key to on.

Even a good working ECU and ISC will make some noise when the ISC homes on powerup or powerdown but it makes more noise when there is a problem.

Steve

 

[shaunman1979]

I got home and checked my ECU for any noticable signs of the caps leaking and didnt see anythng. I dont know where to go from there I could have sworn that was causing it. Well just have to wait and see I guess. Could the caps go bad even if therre not leaking?

 

[steve]

Could the caps go bad even if there not leaking?

Yes and they can be leaking without you seeing anything. If you have original capacitors on your ECU replace them. Don't wait, they have either leaked or they will.

Steve

 

[shaunman1979]

Thanks Steve I am sending it out tomorrow to get them replaced. After the install Ill let ya know if it is still happening.

 

[RSTurboFWD90]

Steve, My ISC clicks continously (never stops) when I turn the key to ON. It's as if it never gets to the point that the ECU says it should stop. Is that normal? Also, I am a true novice with the logger and would like a few tips on what I should look for initially to analyze the bucking problem. Thanks. R