Engine/Transmission (1994 - 1998) Ticking noise, rough idle, and miss

[McCRam]

Lately the engine has been running alot rougher than normal. Usually I throw some extra stanadyne into the tank, and run it down the highway, it will clear up. Not any more. Another new development is when I go to pass on the highway it has a very noticeable miss. It is also making a new ticking noise. It is a very high pitched noise that goes away when I let off the throttle.



The truck is not low on power, (I took down a duramax the other day ) Boost and Egt readings are normal, I even recorded 20. 4 mpg on my last road trip.

I'm thinking that I have a weak injector. Will they make a ticking noise when they go bad?

My other thought is maybe the lift pump is bad. I have not checked pressure yet. I dont have a way to do it.



I hoping the tdr can lead me down the right path before I throw money at it. Thank in advance

 

[NMongeau]

Sounds to me like the injector pump is starving for fuel. If there are no visible leaks I would check your fuel filter. Also on these trucks the lower housing of the fuel heater has a screen in it that may be plugged. Have you tried any treatment in the tank to kill alge that might be in your fuel? Good luck.

 

[Joe G.]

If it's not low on power then the fuel system ahead of the injection pump is probably ok. Does it idle rough? If it does then loosen each injection line nut at the injector. Be careful and only loosen it enough that it leaks a little. If the idle does not change when you do that then the injector or delivery valve may have a problem. If an injecton nut is loosened it should miss on that cylinder. If you find one that does not swap it with a cylinder that is ok. If the problem moved with the injector then you have an injector problem. If it did not they you may have a delivery valve problem.



A fuel pressure gauge is a necessary item for these trucks as far as I'm concerned. In this case if the fuel pressure was ok when you are haveing the problem then it is probably like what I have described above. If the fuel pressure was not ok when the problem occurs I would look at the overflow valve.

 

[McCRam]

Thanks for the reply's. I just changed the overflow valve about a month ago. I checked the spring on the old one and it was short. So I stretched it out and it ran much better at low rpm. I put a new one in after that. Also, I changed the filter and screen less than 3000 miles ago. I guess I could pull them out to see if anything shows up.



I will try Joe G 's suggestion for the injectors. Although I will not rule out anything at this point, I am leaning towards the injection system. When it has the miss, it has a very constant rhythm to it. At Idle it runs rough as well. Actually if I compare it to my uncles 24v, it is rough all the time.



Can the Injectors make noise when they start to go? Thats is what is making me worried. This is a new noise that just developed over the last couple of days. The miss started last weekend on my way back home.



Thanks again.

 

[mechanic]

Thanks for the reply's. I just changed the overflow valve about a month ago. I checked the spring on the old one and it was short. So I stretched it out and it ran much better at low rpm. I put a new one in after that. Also, I changed the filter and screen less than 3000 miles ago. I guess I could pull them out to see if anything shows up.



I will try Joe G 's suggestion for the injectors. Although I will not rule out anything at this point, I am leaning towards the injection system. When it has the miss, it has a very constant rhythm to it. At Idle it runs rough as well. Actually if I compare it to my uncles 24v, it is rough all the time.



Can the Injectors make noise when they start to go? Thats is what is making me worried. This is a new noise that just developed over the last couple of days. The miss started last weekend on my way back home.



Thanks again.

Yes, injectors can make some noise by themselves. But most of the time the noise is caused by a bad injector, which is causing the amount of fuel being injected to be incorrect, and or the injector drips and does not atomize the fuel very well if at all. Because of these problems, the burn pattern is incorrect and it causes the engine to knock or rattle. If you get a chance to watch the shop "pop" check the injectors, you will be amazed at the differance between a good pattern and the pattern from a worn or damaged injector.

 

[DogDiesel]

Lift pump sounds weak. I have a 5. 9L 97 12V in my chevy. I used the chevy oil pressure switch to feed my gage and additionally power on and off my additional electric fuel pump.



Was pushing it hard (@85-90 w 4:10) for six hours to get home to an emergency. The fuel pump quit working once, which is a nice safety mechanism, due to thinning oil. I cooled it down at a rest stop, and restarted, and it worked again. I had accrued oil temps, coolant was only 140.



Symtoms were slight loss of power, less smooth running. Prior to installation of the pump, it ran like this, course mileage was about 1 MPG better, but less power. It has more low end grunt with add on fuel pump, and is so much smoother and nicer to drive.



I'll not run one without a booster pump.



I have the same symtoms with the 4BT in my Bronco, which I intend to remedy with an add-on electric lift pump.



Time for a new lift pump.



I'm buying one for mine before it goes out.



Wayne

 

[Todd T]

your transfer pump could be going out. the ticking could be the rod hammering on the cam lobe. when they start going bad the spring goes soft and allows some slop between the pump and rod.



low pressure could cause hard start, rough idle and eventualy degraded power in general.

 

[SLJolley]

I would have your injectors checked. How many miles does the truck have?

 

[McCRam]

Thanks for the replys

The truck now has 174000 on it. I've only had it for 22000 of them. On the way to work today it ran nice and smooth like usual. Idles nice, and didn't miss. However the noise is still there. I'm not sure if I should waste time and money having the injectors tested. If it turns out that one of them may be bad, I would like to just get a set of 370's. But I guess it is the only way to make sure I have found the problem.



I'm going to hook up a fuel pressure gauge this weekend. Can anyone recommend an easy place to hook into? The gauge I plan on using is a 1 inch autometer pressure gauge. I'm going to mount it under the hood on the firewall or fender.



I hope by the end of the weekend I'll have this narrowed down.

 

[bmoeller]

Do you still have one of your old overflow valves? If you do, take the spring and check ball out. Then you can hook the gauge to that.



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[McCRam]

I knew I kept that for a reason. Sometimes it pays to be a pack rat. That is the kind of easy I was looking for. Thanks

 

[McCRam]

I got the gauge hooked up. It is showing 16 psi at idle and 22 to 23 psi at 2000 rpms. That is with a cold engine if it matters. I have the rear brakes torn apart so I couldn't warm it up. Is this low enough to cause noticeable problems?



I did a search, and I gather that the minimum pressure is 20 psi at idle, and should be around 30 - 35 psi at 2000 rpm. Is that correct? If so I will order up a new pump. Us diesel has one listed for $113.



As far as the gauge installation, I don't think the overflow valve will flow enough fuel through. The holes are half the size as the original bango bolt. So I will put the banjo back in after this is straightened out. Then I will try to drill the overflow valve out at a later date.



Right now it is idleing pretty smooth so I haven't checked the injectors yet. I suppose I colud have to problems.



Again thanks for the help.

 

[McCRam]

I got to take it for a drive this morning. It will get 20 - 23 psi normal driving around town. The most I have seen the gauge read is 25 psi, that was high rpm with no load. But when I get on it, ( 30lbs boost 1300 egt) it will drop down to 8 or 10 psi. I haven't read anywhere that you could pull the 12v lift pump down that low, especially with my mostly stock motor.



So, what is normal output for a 12v lift pump? IS it time for a new one?

 

[bmoeller]

I knew I kept that for a reason. Sometimes it pays to be a pack rat. That is the kind of easy I was looking for. Thanks

You're welcome.



That is what I've saved mine for. Just haven't hooked it up yet.



You could also drill and tap the original banjo bolt, if you want to keep the gauge in place, not just temporary. Won't have to try to enlarge the other holes that way.

 

[Rhondasway]

Have you checked your timing? It can slip (not all that uncommon), going too low, and causing rough running. I would think this could also vary a little depending on weather (?). I'd check it before replacing parts.

Also, that injector test is not difficult. All you need is a step stool and a 3/4" open end wrench for the first part. Swapping 2 injectors is also pretty easy. If you haven't done it yet, we can help you through it.

 

[Joe G.]

But when I get on it, ( 30lbs boost 1300 egt) it will drop down to 8 or 10 psi.

There is a hose that attaches to the overflow valve. Squeeze it closed with a pair of pliers and see what that does to the pressure. If the OF valve is bad the pressure will go high. If the pressure stays low then you may have a lift pump problem.

 

[McCRam]

Thanks for the ideas. I have a new pump sitting on the bench, but I am going to replace the fuel filter and try your ideas before I throw it in. I want to keep track of the pressure each step.

 

[McCRam]

I got the lift pump put in on friday before my road trip. It seems to have fixed all my problems. The truck runs great now. It is still a little rough at higher rpm. I have always suspected that one of the injectors is weak. I am going to get a laser thermometer and see if I see a difference.



Thanks for all the help

 

[Rhondasway]

That's great! Let us know about the high-rpm fix too.