GMC Jimmy Engine Problems. Please Help!

jthaler15jthaler15 Member Posts: 2
edited July 2014 in GMC
I have a 1999 GMC Jimmy SLT 4WD with 87,XXX miles. The other day I ran to the store and back (about a 7 mile round trip). Previous to this trip, I havent had the need to go anywhere for 2 weeks because I wasnt in school. I let the car warm up for a couple of minutes, and then left the house. I have the climate control and I had the temperature all the way to 82 and the fan on high. Usually, it heats up fast and I have no problems. Well it wasnt warmed up by the time I got to the store, and by the time I left, it still wasnt warm until I was accelerating. I immediately looked at my temperature and oil pressure guage. My temperature was running about 225-240. I then looked at my oil pressure guage and it would fluctuate. When I was on the gas pedal, it would run very high, then immediately drop when I let off. We got home and me and my brother immediately checked the compression. The cylinders were reading as this, four of them were 150, and the last 2 were at 115-125. As we checked the cylinders, we saw that the spark plugs were stock platinums, so we changed those. Then, we discovered the main problem was that intake manifold gasket was leaking. So we replaced that, let the RTV settle to for over 24 hours, and put everything back together. We flushed the fluids, and put new fluids in it. The radiator holds fluid, and there arent any leaks. We started it up, and at first it seems that its burning a little bit of oil and the oil pressure was at about 50, where its normally in the 40s. We let the engine run for a good 15 minutes, and it started slowly heating up. But, its idling pretty rough and we cant seem to figure out what the problem is. I did a search, and Im not sure but could it be either the EGR valve, EGR gasket, or some other major malfunction?


  • jthaler15jthaler15 Member Posts: 2
    Sorry, the other 2 cylinder readings were 120-125.
  • tidestertidester Member Posts: 10,059
    Give Jimmy Idle and Stall Problems a try.

    tidester, host
    SUVs and Smart Shopper
  • jwalsh3124jwalsh3124 Member Posts: 1
    I went to start my jimmy up to go to work and my oil pressure topped out at 80psi after a few minutes I put it in drive and and it went to 0 psi I got out and had a puddle of oil down the driveway I checked the oil filter and it blew the seal on it I replaced the filter and oil and it did the same thing 3 times went to 80+psi blew the seal. I tried to flush it with engine flush and while I was doing that it went down to 40psi but when I changed the filter and oil it did it again anybody got any Ideas
  • jerry12345jerry12345 Member Posts: 1
    edited March 2010
    oil pressure relief spring is probably sticking. youll need a service manual and a bit of free time to check it. i havent worked on cars for a while but im pretty sure its in tegrated into the oil pump which is likely inside the oil pan. you may be able to loosen stuff up enough for youy to raise the engine just enough to pull the oil pan out and work on it while its still in the vehicle. you may need to rotate the crankshaft to move the balancer weights out of the way but to do that all you gotta do is turn the flexplate(the big ring with gear teeth on it) at the rear of the engine. (moving the balancers will allow you to pull the pan out with less raising of the engine)

    EDIT make sure you remove the distributor cap before raising otherwise you may crush it. and drain the oil first.

    do not buy a high pressure pump you may buy a high volume but make sure you dont install the high pressure spring.
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