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tvrc18 Forum Newbie Posts 10 |
03-07-12 11:20 AM - Post#2199581
My 99 express van with the 5.7 motor has a weird surge at around 40 mph and up. I have looked at rpm with my scan tool and see a rpm increase of about 150 rpm at about 40 to 45 mostly and then drop back down. It does it quite often like every 5 to 10 seconds. I have done a major tune up, plugs, wires, dist cap, rotor tps replaced. I had a trans shop check my tranny and they installed a new tc and 3-4 clutches and band.The tc was shot and the clutches worn but it still does it. The tcc is staying locked so it is not that and a tech hooked his Tech 2 scanner and monitored some things and noticed the rpm surge but could not pin point the reason. I know my distributor is worn out and I will be replacing it soon,it has side to side play, maybe that is causing it. I have no codes or mis fires just the rpm changes. Could it be a EGR or vacuum issue? I am at a loss. |
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CowboyTrukr "2nd Year" Silver Supporting Member Posts 705 
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03-07-12 10:42 PM - Post#2199859
How does the rpm increase present itself. Is it a gradual increase/decrease or an instantaneous spike up and down? Greg
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tvrc18 Forum Newbie Posts 10 |
03-08-12 05:21 AM - Post#2199889
It is pretty quick, you can hear the motor change tone and my scan tool will jump up 150 or so rpm. I am hoping the distributor will cure it but I don't think it really will. |
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355Cheyenne Senior Member Posts 3743 
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03-08-12 07:32 AM - Post#2199938
I would wait until you replaced the distributor but usually a surge is a sign of a significant vacuum leak.
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tvrc18 Forum Newbie Posts 10 |
03-08-12 08:55 AM - Post#2199962
Funny thing is it does not seem to surge at idle.I thought for sure I had a tcc problem but the tech 2 scanner ruled that out. It showed the slip percent was low too I think about 10%. It is frustrating when you can not find an obvious problem. All the plugs looked really good, one looked alot cleaner than the rest like it was maybe leaner on that cylinder but not sure what that would indicate. Maybe that injector is a little clogged but it seems to run fine other than the surge. |
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355Cheyenne Senior Member Posts 3743
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03-08-12 08:57 AM - Post#2199965
Clogged injector(s) would more likely produce an intermittent miss.
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tvrc18 Forum Newbie Posts 10 |
03-10-12 03:00 PM - Post#2200847
Well I changed out the distibutor and the surge is still there. After the tcc locks up at about 40 or 45 mph the rpm's will jump up from about 1200 to 1350 or 1400 quickly and then return to 1200. What could be causing this, EGR, O2 sensor. fuel pressure? No codes and no misses but it is driving me nuts. |
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355Cheyenne Senior Member Posts 3743
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03-10-12 08:59 PM - Post#2201002
Not surprised but when you know something else is messed up, trying to t/s another problem is difficult because the other problem can mess with your testing results. Honestly your situation is almost always a vacuum leak. Check all the hoses under the hood. Check your brake booster line for leaks. Check the base of the throttle body for leaks. I would even go as far as to pull the brake booster line and plug it as you may have a leak in the booster. Since it doesn't surge at idle but only in drive gear it might be worth talking to a transmission shop, your transmission may be worn out and slipping. How many miles?
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tvrc18 Forum Newbie Posts 10 |
03-10-12 09:56 PM - Post#2201027
I am also thinking maybe transmission. I got a limited warranty when I bought the van and they did replace the tourque converter and 3-4 clutches and a band but that did not fix the surging issue. IT has a bunch of miles 150k but mostly hiway. I may have the valve body rebuilt or buy one just to try it since the 4l60e has so many valve body issues with the tcc. As fast as the surging happens it almost has to be the trans I think. |
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tvrc18 Forum Newbie Posts 10 |
03-11-12 02:01 PM - Post#2201245
I tried looking for a vacuum leak today and had no luck. I did not have carb cleaner but read you can squirt water and get same results. I sprayed all around the hoses for pvc, cannister purge lines and upper intake manifold and no change in engine sound. I think I will take it to the tranny shop and have the valve body checked and maybe the sonnax kit put in it. |
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tvrc18 Forum Newbie Posts 10 |
03-22-12 06:55 AM - Post#2206019
Valve body fixed my surging. No vacuum leak found so I bought a new gm valve body and had a tranny shop install it for me. 
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