4 Cylinder GM Iron Duke Power Question

[Red Rock Jeep]

I recently purchased a 1980 CJ7 with the GM Iron Duke 4 Cylinder and a 4-speed tranny. Years ago I owned an old postal Jeep that had an AMC 232 i6 six with an auto tranny and compared to that one this CJ7 has far less power. On a flat road with no head wind I can barely get the speed up to 45 mph. If there is any incline I have to shift down to 3rd and the speed drops below 40 mph. I am planning to give it a tune up (plugs,wires, cap.rotor) in a week or so, but is this lack of power normal for the Iron Duke, or do I need to have the carburetor looked at? I did change the air filter, but there was no change in power. I did not expect this Jeep to be a speed demon, but I would like to be able to go 55-60 mph on a level road with no curves. Any comments form some 4-cyl. owners regarding their performance experiences would be appreciated. Thanks.

 

[3QuarterTon CJ]

I would say to check your timing, it sounds like it could be retarded a few degrees. If it has high mileage the timing chain could've stretched.

Does the engine run warmer than it should?

Pull a spark plug out, and see if the firing end is white, cardboard brown, or black.

I'd double check the timing, the carb mixture (possible running too lean,too rich), and the tune-up items (plugs[burnt,fouled,old,too much gap], wires[old,arcing,oil soaked,soft], cap[burnt,missing carbon pile], rotor[burnt,missing end electrode] ).

Also make sure the head gasket is ok, maybe you have a bad gasket between two cylinders allowing some coolant into the mix, making her run poor.

 

[RangerRick]

If everything 3Quarter says is OK like timing, ignition, mixture & fuel system etc. check out.....

Check to see if you have a restricted exhaust system like the cataclysmic converter has clogged or broken up and plugged the exhaust. Also make sure the muffler didn't break up inside. Sometimes they will rattle inside and sometimes not. I've seen some weird clogs like pipe de-laminating, cats breaking up, mufflers flattened or broken off and wedged in the exhaust system that caused power to be way down on an engine because it can't breathe or in this case exhale spent gasses properly. Check to see if it seems like a "normal" amount of exhaust gas flow is coming out the tail pipe when the engine is running as compared to another 4 cylinder car but use caution so as to NOT to burn yourself or breathe in the exhaust. Remember the cat gets to 800* F+ to burn off excess gasses in the exhaust prior to exiting the tail pipe. It can over-heat and come apart inside then clog up the exhaust passageway. If you're not sure, take it to an exhaust specialist that can "check" it for you. Someone you know is honest and won't gig you for something you don't need if nothing is wrong.

RangerRick

 

[Red Rock Jeep]

Thanks for info! I will be doing a tune up this weekend and will be sure to check the timing and exhaust flow. If the flow and timing check out, and the tune up doesn't fix the problem I'll move onto the carb.

The water pump went out last week, so I put a new one on and changed all the hoses. The coolant that came out looked fine, so I think the head gasket is good, but I'll check the compression just to be sure.

This Jeep has less than 65,000 original miles and is in almost totally stock shape. I hope I can fix this power problem or my daily drives to work will suck!

 

[cass]

i had a very similar problem with my duke when i got it. it ended up being the charcoal canister having problems. it filled my float bowl on the carb with bits of charcoal. it seemed to run ok but wouldnt run 50 on the highway. i just blocked the line that hooked to the vent on the carb bowl and left all the vaccum lines hooked up to the charcoal canister.

 

[cass]

oh and i also had to take the carb apart and clean it

 

[mncj7guy]

FYI, Your IronDuke does not have a timing belt, it has 2 meshed gears. One is plastic, and has a bad habit of failing (both GM 151 's I have had). Before I blew the gear, I was able to generally get to 65 mph, but started to really have issues before the gear went.

 

[Red Rock Jeep]

I hope my timing gears aren't ready to go! Last week, before I could get to do the tune-up, both front leaf spring shackles broke on my way to work. I managed to get to a shop where it is currently having this issue fixed. Apparently the front wheel bearings are shot too. No doubt now that buying this Jeep was a bad decision. I'll proceed with the tune up since I already have the parts, but I'm considering selling this Jeep before something else major breaks on it.

 

[mncj7guy]

Not trying to scare you. I hope that is not the case either.

The engine is not that bad when running, but 30+ years is a long time for many of the parts. I had one of my shackle hangers break when a shop lifted it up, they tried to hide it. ( never been back, took it somewhere else to get fixed).