Engine/Transmission (1994 - 1998) Slight engine surge

[JacobsonD]

Twice today I noticed a very slight surge of the motor when I started climbing a moderate grade at freeway speeds. I noticed the first time it happened that the throttle pedal got stiff and took a lot of force to press farther for more fuel. The second time it happened, I didn't try giving it more pedal. Instead, I kept steady pressure on the throttle and I noticed ever so slight surging of the engine.



I'm the second owner, and I'm slowly getting to know the vehicle. It has 126,600 miles and is fairly stock. However, this past August I had to get a new cam (it's a 215 cam) and pushrods for the #2 cylinder because the previous owner completely screwed up that cylinder when putting in the 60# springs for the PacBrake. The mechanic also put in a different fuel plate. He thought that I'm probably making somewhere around 220HP.



I was planning to change the fuel filter this weekend. Am I on the right track to suspect some sort of fueling problem. Could it be as simple as a fuel filter restricting flow when more fuel is demanded? Is this a sign of a fuel pump issue? I just happened to change the air filter today before the surging started.



By the way, I was empty and not towing. This is my daily driver, and I sometimes tow a 25' travel trailer. I towed the trailer over Thanksgiving and didn't notice any surging, and I had plenty of power climbing the hills while towing.

 

[JacobsonD]

Here's some info:



Today the problem is a little worse. I did some experimenting, and I noticed that if I keep steady or increasing pressure on the throttle, the loss of power gets worse when this weird situation occurs. But if I let off the throttle just a little bit and then get back on the throttle, the motor runs like a champ again. Any ideas?



I'm still thinking (hoping) that it's just needing a fuel filter change.

 

[HerbW]

I have a 98 12 valve also with the same problem. I changed the filter and still surge if I'm at 1500 rpms or lower and going uphill. It's either torque converter, transmission or an engine miss. I wish I knew. You have an old post. Did you solve the surge? Thanks. Herb

 

[JacobsonD]

No, I haven't solved the problem yet. I replaced the fuel filter and it didn't affect the problem at all. I am now wondering if I have a vacuum leak somewhere. I talked to a mechanic and he thinks that there's a problem with the vacuum to the waste gate. I hope I'm explaining this correctly. I loose boost when this happens.

I've also noticed that lately when I start the engine in the morning now that the mornings are cooler (in the 40 degree range), the exhaust brake is very slow to engage. This is also vacuum operated. Or is the exhaust brake actuator just stiff with the cooler morning temperatures?

Still searching for the fix...

 

[HerbW]

Could the waste gate be sticking open? Then you're loosing your pressure? You do has gauges to monitor boost and lack of it, don't you? Good luck. Herb

 

[JFaughn]

I have maybe the same thing , I describe it at about 1,200 rpm , just maintaining speed , high gear & lock up , a slight surge , drive through or above 1,350 rpm & higher , it goes away .
Been watching posts about this for some time , but I haven't done anything yet , so I'm still in the theory stage , with somewhere around 20-30 different things we can do for tunning the 12v , there are many possibilities , my guess is its responding to either or both of 2 points , 1st slipping TQ & low pressure [ because of the low rpm ] , 2nd maybe its just the right conditions for you to feel some reaction / resonance of the pulsing of the lift pump .

 

[JacobsonD]

Hi Herb,

I think it is the waste gate opening. It's weird. It'll be generating around 15 to 20 psi of boost, and then it drops off to around 8 psi. If I back off the throttle for a moment and then get back on it, the engine will usually start making boost again. I'm trying to figure out how to track this down.

Thanks.

 

[JacobsonD]

One other note. I have boost and pyro gauges, but I don't have a fuel pressure gauge. Could it also be related to a fueling problem?

 

[MMcCallie]

I experienced extreme lack of power and very stiff throttle this summer. I took off my AFC and discovered that TLSE Turbo Systems who had ground and welded and reground on my fuel plate, had reinstalled it so that the governor arm was going under the plate, causing it to hang up. Haven't had stiff throttle since i fixed it, worth a peek to check on yours. This same mechanic almost stripped the threads for one of the AFC bolts. The bolts don't need to be that tight, its just a cover so oil doesn't splatter out-good to know when you put it back together.

 

[JacobsonD]

Thanks. I appreciate all input. I'll take a look at the AFC.