Sluggish 87 350 tbi

[Jerry phillion]

my 87 tbi starts good, runs good , idles good, but it's sluggish when driving down road. I have to push
Pedal way down to almost downshift before it will pick up much speed. Once it picks up, it pulls hard.
But that " in between " is driving me nuts. Could it be the tp sensor or maf sensor? Or what? Maybe
Someone else had this same problem. thanks

 

[4WDKC]

It can be anything look for either a used scanner to access live data or google the DIY cable, with out either of these its like trying to tune a carb while deaf and blind.

 

[1987 GMC Jimmy]

No SES lights when this happens?

 

[Jerry phillion]

What is ses lights? I will try diy Google.

 

[chengny]

What is ses lights? I will try diy Google.

SES = Service Engine Soon - the equivalent of a Check Engine light.

If illuminated, it indicates that there are one or more DTC's (digital trouble code) stored in the memory of the ECM (electronic/engine control module).

DTC's can be pulled with a scanner or just a paperclip. Hit the link below to see how to do it with a paperclip:

http://www.gmsquarebody.com/threads/no-start-situation.19622/#post-362841

BTW - your initial suspicions as to the cause of the problem (TP & MAP sensors) are # 2 & 3 on GM's fuel system related things to check when "hesitation, sag or stumble" is occurring. Only low fuel pressure is ranked higher.

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[yevgenievich]

kind of joining on a slugish tbi topic.

On my 91, it just appears to be a lot slower at all speeds compared to my 94 truck. Both 350 tbi with 4l80e and a 14 bolt(sf vs ff). Gearing is different, but it appears to be at any speed. 91 has all new ignition components, has better compression, but yet just appears to have %30 less power. No codes.
Does the roof and front axle of a suburban really has that much more weight over a crew cab to be that noticeable? Or did gm threw a better cam in towards the end of the tbi production.

 

[4WDKC]

kind of joining on a slugish tbi topic.

On my 91, it just appears to be a lot slower at all speeds compared to my 94 truck. Both 350 tbi with 4l80e and a 14 bolt(sf vs ff). Gearing is different, but it appears to be at any speed. 91 has all new ignition components, has better compression, but yet just appears to have %30 less power. No codes.
Does the roof and front axle of a suburban really has that much more weight over a crew cab to be that noticeable? Or did gm threw a better cam in towards the end of the tbi production.

Your 94 could be a roller cam engine that made its way to a truck, also the burban weighs alot as it has to have more support for the additional roof and glass. Best way to know is get a scanner on it and see the live data.

 

[yevgenievich]

Your 94 could be a roller cam engine that made its way to a truck, also the burban weighs alot as it has to have more support for the additional roof and glass. Best way to know is get a scanner on it and see the live data.

I scanned it before and all looked fine. Just good bit slower than the 94 one ton. Was just hard to believe for it to be that much heavier than the crew cab one ton. I guess it might be a combination of a better cam and less weight on the 94. The only other item I think left to verify is to take a look at the catalytic converter and make sure it is not clogged.

 

[4WDKC]

I scanned it before and all looked fine. Just good bit slower than the 94 one ton. Was just hard to believe for it to be that much heavier than the crew cab one ton. I guess it might be a combination of a better cam and less weight on the 94. The only other item I think left to verify is to take a look at the catalytic converter and make sure it is not clogged.

It could a group of smaller factors that add up, different gears (373 vs 410), tires (33s vs 31s), weight, flat tappet cam, partially plugged cat/restrictive exhaust. Also old/worn out/slow responding sensors can play a part in it.

 

[yevgenievich]

Looked up engine option from heritage info and the papers show both to be exactly the same, 190hp and 300 lbs ft(those are for hd 5.7 version, both get less peak than regular 5.7 but more under the curve). Took a couple of back to back drives and at lower speeds it might be weight and gearing, but at 55mph and up the crew cab pulls much better. Might be gearing,weight and air resistance. Really like the 4.10 gears over the 3.73's on a stock tbi. But it is cheaper/more rewarding to swap in a big block than regear front/rear axles

On my side conclusion is that i probably made it all up