Power surge at 2% to 90% throttle..

[Camar068]

A clogged cat will heat up faster than normal also correct? If you have 2 you can scan the temps after a 2 minute warm up. If the temps are way off then the hotter could be clogged. You may only have one though.

 

[capt_yoda]

Been mechanic'ing on Chevy for a lot of yrs, haven't miss placed wires according to firing order since I was a teenager..lol, but I did double check... and as for the CAT, it's a high Flo I replaced last year, had to trash that pancake OE cause their horrible for restriction..

 

[CSFJ]

well' you've checked everything else, for ***** and giggles have you done compression and leakdown checks lately? maybe hook an old school vac gauge up and watch what the needle is doing? It seems as though you've pretty much eliminated most everything else outside of the hard mechanical parts.

 

[1987 GMC Jimmy]

A clogged cat will heat up faster than normal also correct?

Yep!

 

[capt_yoda]

The only thing I do know, is it idles great, and it will run like a scalded ape when throttle is to the floor.. but in between 2%-90% throttle, it's terrible... I have heard different suggestions from other forums... such as:
Intake has clogged EGR ports that connect to the head..
A failing Fuel injector..
Or a failing distributor..
Opinion??

 

[CSFJ]

what's the injector spray look like when you manipulate the throttle arm?

 

[capt_yoda]

The engine only has 85k miles on it, but original motor from 87'... the compression check was normal for all 8cyls.. that was done 4 days ago.. and the Vacuum test was good, not great, but satisfactory level and it was not erratic, it was steady through all rpms...

 

[CSFJ]

I'm not too familiar with the newer distributors, but it does sound like a possibility. excessive play in the shaft maybe?

 

[capt_yoda]

The injector spray is a nice cone shape, no dribbles, or partial sprays... and both looked good across the rpm band from idle to 3500...

 

[capt_yoda]

The distributor has very little play under the cap, (turning the rotor has very little movement), the retainer is tight and number 1 is pointed towards the number 1 cyl.. again, timing is near perfect, if not perfect..

 

[1987 GMC Jimmy]

The only thing I do know, is it idles great, and it will run like a scalded ape when throttle is to the floor.. but in between 2%-90% throttle, it's terrible... I have heard different suggestions from other forums... such as:
Intake has clogged EGR ports that connect to the head..
A failing Fuel injector..
Or a failing distributor..
Opinion??

I always pick as much carbon out of the port as I can whenever I have the EGR valve off, and it's always done fine just doing that. You can look at the spray pattern on the injectors. They should be perfectly conical, and they spray should get heavier with more throttle. Anything that's drippy or sloppy may be a dirty or failing injector. The only way that I'd suspect the distributor is if your base timing was good, but your total timing was not because your distributor isn't advancing properly. Have you checked the connections on the ESC module? I don't know any kind of test for it, and you're not getting a Code 43, but it's another thing to consider if you haven't checked that out. My response came a little late. I guess you can mark injectors off that list.

 

[CSFJ]

I can't recall, do these distributors have advance arms that swing out with centrifugal force, or did that end with the older style?

 

[capt_yoda]

That ended with the 1st Gen HEI... I did check the advance while using the timing light and scanner, it's advancing with'in normal limits while loading rpms...

 

[capt_yoda]

And those EGR ports were cleaned before I put the new EGR on, but the where the ports meet, head to intake, the only way to check is to remove the intake to see if there clogged.. and I haven't tried that... but has anyone heard of that, and would it cause my symptoms?

 

[CSFJ]

I had an'89 s-10 once. idled decent, but didn't run worth a damn at light load say, rolling through town at 35-45 mph. WOT was ok. turned out the egr vacuum diaphragm had rusted off from the base. it was just kinda sitting there. I guess I brought all that up to say, it may be time to look at the egr port through the intake to the heads.