E7 350 Turbo lag

[rhinoo]

Got a new to me 98’ 688s with an e7 350. I noticed a slight turbo lag when I test drove it but once I finally hauled a load the lag was worse. It seems to take a few seconds to get under the turbo before it picks up. No smoke at all. I actually choked the motor out twice down shifting going up a hill.  The shift was made in plenty of time but the turbo delayed so long the motor kept going down. The second time I tried to drop 2 gears but it still didn’t pick up in time. If I keep the motor wound up it does decent. I own several trucks and drove them all, even a Mack 96’ 613 with an e7 427 and it doesn’t fall on its face like that at all. So, I was thinking maybe not getting enough fuel but I was also wanting to make sure it has the correct turbo on it. Does anyone know what turbo should be on this motor? I was thinking tomorrow I will also try to check the fuel pressure. Does anyone know what it should be?

[R.E.D]

I believe that truck should have a s300 turbo.

Have you replaced fuel filters ?any fault codes ? lightning ⚡ bolt on?

[Onyx610]

Any chance you can put a gauge on it and get some boost pressure readings? Might be a good place to start. Along with fuel pressure like you said. I believe it’s 70-100psi

[rhinoo]

16 minutes ago, R.E.D said:

I believe that truck should have a s300 turbo.

Have you replaced fuel filters ?any fault codes ? lightning ⚡ bolt on?

I did do a full service on it once I got it home. No check engine light. 

[rhinoo]

17 minutes ago, Onyx610 said:

Any chance you can put a gauge on it and get some boost pressure readings? Might be a good place to start. Along with fuel pressure like you said. I believe it’s 70-100psi

Yea, I think that is the next step if the turbo is correct. Can I tap in at the inlet on secondary fuel filter? 

[rhinoo]

3 minutes ago, rhinoo said:

I did do a full service on it once I got it home. No check engine light. 

 

[R.E.D]

7 minutes ago, rhinoo said:

I did do a full service on it once I got it home. No check engine light. 

Does the lightning bolt come on when the key is put in the on position ,then turns off after a few seconds? The reason I'm asking is because the bulb could be burnt out?

Have you checked for boost leaks? They can be heard easier with both windows down going down the road.

Edited December 7, 2021 by R.E.D

[R.E.D]

6 minutes ago, rhinoo said:

 

That's a s400 turbo, I believe that turbo was for 400hp+ engines .but someone here can check it for sure if you provide the last six of vin.

Edited December 7, 2021 by R.E.D

[Onyx610]

You can call Mack and give them the last six and they should be able to tell you what came on the truck. Also You can tap into it there. One of the other guys might have a better spot. red is correct on the turbo, most guys put that on and pair it with a set of bigger injectors. 

[R.E.D]

If it is the incorrect turbo that someone put on prior to you owning the truck, then most likely would explain the lag 

[Onyx610]

From what I can remember I think red is correct with the s300. Let me take a look at one of our RD688s 350s turbo tag tomorrow morning.  

[rhinoo]

Ok, I will check to be sure check engine light is working when I key up in the morning. I did already change the air intake boot on turbo because it didn’t look real good when I serviced it. I was looking all of them over closely earlier tonight and there is another one that doesn’t look great either but haven’t checked for leaks. Is there enough pressure when idling that soapy water would show a leak? Vin# 037403… if that turbo happens to be upgraded I guess I would need to check injectors to see if they are upgraded also. Should this truck at least puff a little black smoke? Especially with lugging and turbo not spoiling up?

[R.E.D]

3 minutes ago, rhinoo said:

Ok, I will check to be sure check engine light is working when I key up in the morning. I did already change the air intake boot on turbo because it didn’t look real good when I serviced it. I was looking all of them over closely earlier tonight and there is another one that doesn’t look great either but haven’t checked for leaks. Is there enough pressure when idling that soapy water would show a leak? Vin# 037403… if that turbo happens to be upgraded I guess I would need to check injectors to see if they are upgraded also. Should this truck at least puff a little black smoke? Especially with lugging and turbo not spoiling up?

It will build some pressure but engine fan will blow the bubbles off.the way I test the intercooler is by capping both sides off with plumbing pvc caps..one of the caps drilled and tapped for 1/4 inch npt fitting..then apply some pressure and soapy water.

[R.E.D]

10 hours ago, R.E.D said:

It will build some pressure but engine fan will blow the bubbles off.the way I test the intercooler is by capping both sides off with plumbing pvc caps..one of the caps drilled and tapped for 1/4 inch npt fitting..then apply some pressure and soapy water.

Here's my set up..cap fits inside intercooler boot.put clamp back on ,not too tight , then apply shop air, don't put too much pressure as you could damage your intercooler, 20psi should suffice.let us know.

Red

Ps: I couldn't find my 1/4 npt tap so I just heated the fitting with a torch and made the threads that way.then put a nut in the inside for safe measure.😅

 

Edited December 7, 2021 by R.E.D

[Vmac3]

May be a governor setting. I would hook up the service software and check to see if the gov is set to min/max rather than all speed.

V

[rhinoo]

38 minutes ago, Vmac3 said:

May be a governor setting. I would hook up the service software and check to see if the gov is set to min/max rather than all speed.

V

Ok, is this engine a vmac l or vmac ll? Or something different?

[rhinoo]

41 minutes ago, Vmac3 said:

May be a governor setting. I would hook up the service software and check to see if the gov is set to min/max rather than all speed.

V

Also wanting to check fuel pressure today. Do you know what it should be coming out of lift pump? Thanks

[Joey Mack]

V-Mac 1

Edited December 9, 2021 by Joey Mack
Poor spelling

[Vmac3]

56 minutes ago, rhinoo said:

Also wanting to check fuel pressure today. Do you know what it should be coming out of lift pump? Thanks

28-49 psi

[rhinoo]

43 minutes ago, Joey Mack said:

V-Mac 2

I’m looking at truck now and has no ecm, manual foot throttle, with Bosch inline pump.. I sat on phone with Kentuckiana Mack for 30 mins for them to tell me it was an e7-350. 🤦‍♂️

[theakerstwo]

Some E7 350 was a mechanical engine.

[Vmac3]

Oh shoot. I just noticed the stop lever on one of the other pics. 

That engine is an E7 mechanical. Fuel pressure should be 23-39 psi.

My apologies.

V

[Onyx610]

44 minutes ago, theakerstwo said:

Some E7 350 was a mechanical engine.

Yup, we had a 98 with 45,000 miles that we gave away for 40k….

[rhinoo]

24 minutes ago, Vmac3 said:

Oh shoot. I just noticed the stop lever on one of the other pics. 

That engine is an E7 mechanical. Fuel pressure should be 23-39 psi.

My apologies.

V

Ok, thanks. Is the mechanical a good thing or bad? Trying to get teed into fuel system now but gotta go pick up a fitting. I talked to a guy at Rochester diesel earlier and he said that if someone put that s400 on without upgrading the injectors that it would be sick. I told him I was gonna check fuel pressure first and if it was ok I would call him back and order a set of injectors. 

[Vmac3]

10 minutes ago, rhinoo said:

Ok, thanks. Is the mechanical a good thing or bad? Trying to get teed into fuel system now but gotta go pick up a fitting. I talked to a guy at Rochester diesel earlier and he said that if someone put that s400 on without upgrading the injectors that it would be sick. I told him I was gonna check fuel pressure first and if it was ok I would call him back and order a set of injectors. 

That is a very reliable engine. Don't expect the truck to be a rocket, but it is very good.

V