Low power/misfires

[Cbracey96]

I want to get my 740 going again but actually get it right. It’s alway had the misfiring and low power. Not sure where to start. It has the fuel pin groud down and a t3t4. That about all I know about the car

https://youtube.com/shorts/U8FXy7fkyYk?feature=share
https://youtube.com/shorts/JgHcENiBRx8?feature=share

[ngoma]

Yes indeed hard to know where to start. I have little experience with those two particular mods.

So you know nothing about the car or its history?

[Cbracey96]

I don’t really know that much about it. It supposedly has head studs. I do know a guy on here owned it, I believe his name is “stroked383”.

[v8volvo]

Never hurts to start with the basics right?

Engine needs good compression, good supply of fuel, good supply of air, correct base engine adjustment (cam timing, pump timing, valve clearance), and correctly functioning injection pump and injectors to run well.

If it has those things, it WILL run well.

I would make a checklist of steps and go through them systematically if you want to make it right.
- routine maintenance (fluids, filters)
- compression test, and have injectors tested and as necessary cleaned/reset/rebuilt while they're out for that by a qualified shop
- timing check, timing belt replacement if necessary
- valve clearance check, adjustment if necessary
- fuel system examination, check for excessive supply restriction and air intrusion

These things should go a long way towards getting it running normally, regardless of the modifications.

[v8volvo]

I watched your videos and it doesn't sound too unhealthy to me other than obviously the fuel pump needs to be turned back down to get rid of the smoke.

You say misfiring and low power? When and how does it misfire? At idle, under load, ?? Is it a steady miss like a weak or dead cylinder or is it an intermittent stumble or what?

[Cbracey96]

Under load. Probably starts around 1500rpm to 4000

[v8volvo]

Steady misfire from one cylinder?

Or intermittent bucking/stumbling/hesitation?

When was the fuel filter last changed? Replace it if in doubt and make sure not to double up the inner o rings.

How well does it start when cold? When warm?

Have you checked valve clearances recently?

[Cbracey96]

It’s pretty hard to start cold. Warm not too bad last time I drove it it had put new filters on it. It does have a blue haze at idle

[v8volvo]

The most valuable questions above I'm going to reiterate again below.

Keep this in mind: The word "misfire" can have many meanings, from a predictable dead miss to an intermittent stumble. It means different things to different people. Both of those problems would probably be called "misfiring" by a driver, but they would have completely different causes and would send you down very different diagnostic paths.

The answer to these two questions is the key to figuring this out. Until we know this answer, we don't know what direction to go in for trying to pinpoint the trouble.

Originally Posted by v8volvo

Steady misfire from one cylinder?

Or intermittent bucking/stumbling/hesitation?

[ngoma]

Originally Posted by Cbracey96

I don’t really know that much about it. It supposedly has head studs. I do know a guy on here owned it, I believe his name is “stroked383”.

Are you able to research his posts to find out more about it? I don't presently have the time to do it for you unfortunately.