Highway speed - shudder, surge

[quickstrikeusa]

Engine surges when throttle is held at a constant speed around 50 -55 M.P.H.

Engine check light is off and no codes

1990 Chevy Silverrado 3500 5.7liter

 

any suggestions what could be the problem

 

Thanks in advance

John

[boomer 33]

Engine surges when throttle is held at a constant speed around 50 -55 M.P.H.

Engine check light is off and no codes

1990 Chevy Silverrado 3500 5.7liter

 

I have the same thing on my 99 Tahoe with the 5.7, any suggestions.

[boomer 33]

Mine is the L31 . 1998 Tahoe. Has new head gaskets and intake gaskets. Plugs are good. fuel filter replaced. Shudders going up a hill and then quits if you catch another gear. Seems like it is missing when it does it. No smoke.

[Nytemare]

Sounds like trans slippage to me. Try changing the fluid and filter.

[plainvanilla]

Sounds like trans slippage to me. Try changing the fluid and filter.

 

 

You mentioned shudder in your title.

If it is shudder on highway speeds, it it likely the lock out converter which was real common in the 700-R4 tranny.

Changing fluid may help for a little while. Best thing for it is some friction modifier additive like Shudder Stop from Dr. Tranny, BG makes a good one too.

 

I had to put a pint in my 01 Caprice once a year for 2 years to doctor mine along till I traded it in.

 

The lock-up converter hits and doesn't freeze up immediately and skips or shudders a little somtimes shaking the vehicle pretty good in the process

[plainvanilla]

If it ends up being tranny, here is the stuff I used

 

Shudder stop

 

I used a hose and hand siphon pump and pumped out about 5 quarts of oil fluid thru the dipstick tube, added fresh in and a tube of this and it kept from going out for about two years.

[boomer 33]

Ok Thanks, I dropped it off at the dealer tp put it on the tch 2 and see what it says. Once theyu narrow it down I will get it back and fix it or at least take it to somewhere that they don;t charge $85.00 and hour!

[workinallthetime]

both sound like ignition to me

the 90 most likely has a bad plug wire.

drive at about 45 mph just to bearly get into o/d then lightly accerlate and see if it does it. i am betting its your wires, get a set of taylors and see if it cures it. 50 bucks

 

the 98 open the distributor cap and look for moisture big problem with those dist caps. you will need a torx bit to open it up and check. Get a new GM made cap and clean out the dist.

[last one]

Here is my story, still unsolved...

98 Silverado 5.7 still misses under load. Recent ride with Autoxray 6000 scanner reveals misfire on 3, 6, and 8. Timing varies from -8 to +33 depending on acceleration and declaration during the drive cycle. wires, plugs,rotor cap, dist cap all replace with AC/Delco brand parts within the last few months, no change. Also replaced the cam sensor. CSPI changed out by Chev Dealer under "Special" for free to MFI Injectors. Fuel pressure good. TPS good, Dist gear is good. Compreession is 185-195 on all 8 cyl, 120K on truck. Vacuum steady at idle, drops quickly at rev up and returns quickly to about 23-25. Change fuel filter and air filter. I have been working on this about 2 years off and on. Worse in the summer with A/C load on engine.

[boomer 33]

Lat one, sounds like yu might need to move on the the tranny?

 

Anyway, The tech 2 showede random miss on all cylinder. Replaced the plug wires and the distributer cap. All is good now. No more miss. I also had them clean the injector tips while they had it. I am glad it is running good again but didn;t help to narrow down what the EXACT cause was, although I suspect it was the wires since the plugs had been replaced several times and it probably casued some degradation of the wires from putting them on and taking them off, along with the age.

[last one]

Not the tranny, had it rebuilt @ 110K, tranny man checked it out 1st. It runs and shifts too well most of the time to be in the xmission. Hope to get the cam retard set/checked this week

[last one]

Anyway I can use a 2 Channel osciliscope to compare the cam to the crank to set the cam retard? Pins to scope??

[boomer 33]

Well h#LL. Turns out that my GF's Daughter didn't want to hurt my feelings after I spent all the cash getting items fixed. The shudder is still there she says. Have not driven it yet myself. Back to the drawing board.

[last one]

I found an independent shop to check/set cam retard today. They had a nice Snap-On scanner for about 8000.00

I had played around with the distributor position the other day and had it turned as far clockwise as it would go in the slot. His scanner showed Cam was at -12 degrees, a bit off from ZERO!

The Snap On procedure is to rev the motor to 4000-5000RPMs to force the computer to relearn the setting. They tried this twice with no luck. Mechanic then loosed the dist, turned it a bit and it now showed -11. He then retried the rev the motor procedure and before it hit 3000 RPM,s it retaught itself. Now the cam setting was a 0 degrees. He locked it down and I am good to go. They charged me $50. A good deal as other places wanted $150 and I had to leave the truck. I found out our motor has a rev limiter and at 5200 RPMs it starts shutting down to keep from blowing it up. No misfires recorded since I rerouted spark plug wires at distributor. Truck runs great uphill with AC on, back off then shower down..... It GOES

[boomer 33]

Hey Last one,

 

do you think this could be my problem also? The Chevy dealer took it for a ride with the laptop hooked up to it. Said cylinder 4 and six showed valves sticking. I was going to replace the heads unless you think this might be the problem with mine also. I guess the dealer would have the electonics to set the cam timing also or is it something you have to check around to see who has it kind of thing?

 

Thanks, boomer