Bogs down in 2nd gear

[pallettagger]

Hi
I have a 1999 Chevrolet p30 7.4 L. Workhorse.
In 2nd gear it's like it won't tach out and bogs down.
I had it in the shop (Chevrolet dealership) and was told it was the knock sensors.
They replaced them and it did not fix the problem. I have no faith in the dealership here, had it at two other shops and they couldn't figure out what the problem was.
They told me to take it to the Chevrolet dealership.
It's hard to find a shop that will work on motorhomes here where I live.
The shop cleared the OBD codes and as of yet no service engine light has came on.

Any ideas on what might be causing this would be appreciated.

Thanks
Geri

[Unplanned Tourist]

Do you have a Mass Air Flow sensor? They can cause a problem like you described. If you do, clean it with the special spray cleaner made for cleaning MAF sensors.

[Soppy]

Could be low fuel pressure caused by a bad fuel pump or partially clogged fuel filter . The only way to tell is connect a fuel pressure gauge and take it for a drive. It could also be the ignition timing not advancing enough. You need to monitor the "live data" from the engine while driving . It will tell you the knock counts, timing advance, throttle position, fuel injector duty cycle , etc. I run "Tuner Pro" software on a laptop for monitoring on mine. Any shop with a good scanner should be able to do the same.

[ArtJoyce]

Only is second gear??? Not in first or 3rd or higher? If that is the case, I would be thinking something with the transition or shifting assembly???

Have you had it to a transmission shop?

[pallettagger]

Hello
Ok thanks guys, I will check for a MAF sensor.
There is one shop here I'll check with to see if they will work on a motorhome.

Geri

[pallettagger]

Art Joyce

Thanks,
Yes only in 2nd gear,, had a friend thinking maybe the same thing.
Had my transmission serviced recently nothing was said and I believe the problem started before that.
No haven't had it to a transmission shop.
I'll get ahold of one and see what they say.

Thanks
Geri

[Adaycj]

Just a thought. Are you sure it is shifting? Transmission shift solenoids can fail, as can the harness connected to them. You'd be stuck in 2nd forever if both fail to work.

Use a cheap OBDIi tool or dongle and watch RPM as you drive and verify the 1-2, 2-3, and 3-4 shift are really occuring. The jumps in RPM should be significant, don't be fooled by the smaller 100 RPM ish jumps from the torque converter clutch. The simplest way is a heavy throttle run all the way to 4th from a stop, but safety may curtail that method.

[edgray]

Originally Posted by pallettagger

Hi
I have a 1999 Chevrolet p30 7.4 L. Workhorse.......

Geri

Not that it matters to your issue, but it MAY be helpful to know that you apparently have a P32 chassis, that could have been built by either Chevy OR Workhorse, but not both. 1999 was the first model year that Workhorse existed. They bought the Chevy RV chassis business from GM and began assembling them in Union City, IN.

IF yours was built by WCC, the vin # will begin with "5B4", otherwise it will begin with a "1" if built by GM. The tenth vin position is a code for the model year.

Regardless of which company built it, your tranny will be the GM 4 speed known as 4L-80E or 4L-85E.

Good luck finding what is the problem.

[donr103]

2 things.. most box a/p store will rent fuel pressure gauge for free.. test fuel pressure many of us have gone to independent fuel pressure gauge on dash.. see GLOWSHIFT.COM.. takes 10mins to hook up.. takes longer to decide on where to mount gauge.. you tube KEVIN CAUDILL fuel pressure gauge

Next if you plan to keep.. you have to get yourself a good scanner.. the more expensive the better.. a good starting point is around 200.00 this will record live data. And help you figure out problems with out codes.. follow Chevy truck 2500/3500 you tube repairs

You have fallen in same black hole most of us have.. where no one can be trusted to make repairs.. or no one willing.. great just keep your money in your pocket not shop..

You know by now.. gm/chevy/workhorse used same light duty truck eng and trans in rv as pickups.. so grab a basic automotive repair book for Chevy c2500 same yr and this will give you trouble shooting guide and engine specs and trans specs.. it will save you a lot.. I use Haynes and Chilton.. you can order online..

Next basic tune up.. when was last time you done one.. plug wires burn I up fast and some times inside.. so do resistance test on each one, while wiggling.. put socks on them..
Change o2 sensors.. and while they are out check back pressure of exhaust.. your cats could be dirty ..
90% of time.. it is weak or bad fuel pump.. so no only record pressure at idle record while driving with helper.. do this.. before changing fuel filter and after..
There is a good start .. report back
Good luck and keep us posted

[1972VWbus]

A bad TPS (throttle position sensor) can also cause the issue you describe. A live scan app pn your phone will allow you to see the TPS reading from 0-100. It should be smooth and not jittery (reading).

[rxvrob]

I have the same rig and in second gear,around 40 to 45 miles an hour it was sort of bog for a little bit but it’s the torque converter locking up. It only lasts for maybe one to two seconds does that describe your problem

[pallettagger]

Hi
Just a follow up.
I'm in contact with a couple different shops to figure out the problem.
Just wanted to let you know I haven't forgot.
I'll post when I have gotten it fix so others may be helped at a later time.

Geri

[1972VWbus]

Originally Posted by pallettagger

Hi
Just a follow up.
I'm in contact with a couple different shops to figure out the problem.
Just wanted to let you know I haven't forgot.
I'll post when I have gotten it fix so others may be helped at a later time.

Geri

Thanks for the feedback.


It could be an issue related to...


1. Ignition related


2. TPS


3. Wonky shift solenoid

[pallettagger]

Hi
Thanks everybody for the tips on what may be the cause.
I had the motorhome at the local Chevy dealership, with supposedly genuine GM techs.
They could not find the problem (which doesn't surprise me) so I'll keep looking for some place that has a real mechanic not just a computer reader (no service engine light on).

If and when I find out the problem I'll post back.

Thanks everyone.
Geri