Can't do 55!

[77 cc lb]

Hi, I have an 88 suburban with a 454/th400 trans. I was going down the hwy the other day and the engine sounded like loud drone noise. After that I couldn't go over 60. The truck sat for a few hrs and when I went to drive it home I couldn't go over 55. The trans shifts out all 3 gears.  Not a clue what could cause this? Any suggestions would be helpful, thanks!

[Irish_Alley]

Fuel or timing check your distributor first

[bd]

Check the exhaust backpressure for possible restrictions.  Should measure under 1.5 PSI @ 3,000 RPM.

[Irish_Alley]

BD not saying it can't be that but I just had this problem with my truck (open headers)  don't know what changed it but seams to run better now with 91 Oct. In her don't think I adjust the distributor

[bd]

None of us can say with any certainty what's wrong, we're not there.  They're just things to check.   

[Irish_Alley]

Lol I agree 100%  but I was also looking for answers also

[77 cc lb]

Is it possible the catalytic converter is bad? It still has the original exhaust!!!

[nlauffer]

very possible.  About a year ago I was driving my Fire Response Pickup, a 2007 F250 with V10, and it started to act the same.  I was only able to go 60 or 65 which wasn't noticeable at first, but after I shut it off and a few hours later got in to leave, I could barely go 40 and it got worse.  Luckily I was only about a mile from the Ford dealer and it drove OK at 30 through town, but when I would have to stop and go again it tried really hard to get moving.  This particular truck has 4 cats in an assembly.  The Ford dealer said two were plugged and they warrantied them due to emission standards.  Truck ran great. 

Does your truck need a cat?  I mean does your area require them to pass emission tests?  Kansas doesn't check is why I ask. 

Either way, if you can drill a whole in it, or if you have one with the tube on the side, you can remove the cap.  If it improves, that's probably your problem. 

[Irish_Alley]

From what I remember cats will get worst the hotter they get and will glow cherry red

[77 cc lb]

Thanks for the info guys!  In NC vehicles 95 and older don't need emissions. So I was going to eliminate it all together. @ irish, I just put new cap, rotor and plugs so could it be the distributor itself? @ nlauffer, my 04 explorer just died when the cats went out. Not sure what happens when cats go out in the older vehicles!?! Thanks again for info!!!

[Irish_Alley]

i was referring more to timing but also check the connections on everything.

[rich weyand]

If the distributor isn't clamped down properly, it will drift retarded.  That would do it, too.

[Irish_Alley]

the more i think about, the more im siding with a restriction problem but check the spark plug wires anyway. could be exhaust or fuel. hows your choke working? does it do this when its open and closed? any idle issues? last time you changed fuel filter/s? if you plan on doing so cut the cat out before you do anything so we can eliminate that as a possibility or find it at fault.

[rich weyand]

First thing to do is throw a timing light on it.  Easiest.

[nlauffer]

If you put new cap, rotor, and plugs - double check all that.  Take a hold of the cap and try to turn the distributor both directions.  If it moves the clamp is loose. 

I bought a 76 Mercury Grand Marquis with a 351M as a derby car.  The owner said it would barely run.  As I drove it home, she was right.  I popped the hood and they had a Chevy firing order on a Ford motor.  Not saying yours is that far off, but if you are one plug off it wouldn't run well.  Rotor and plugs, probably not a problem.

Another really easy check is wait til dark or in a dark garage and open the hood while the truck is running.  Check the plug wires for blue sparks.  Probably won't act like you are describing, but it is an easy check.

My guess is still on the cat.  If you are eliminating it, then poke a whole in it towards the front or just remove it.  The honeycomb type material (I don't remember now what the material actually is) will heat up and melt.  This can eventually clog up most of the exhaust flow.