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1988 Suburban won't run


The Barmy Scotsman
02-04-2006, 07:05 PM
I have an '88 suburban, 350, 4x4, auto, 1/2 ton. It suddenly died one night while I was turning a corner. Since, it won't idle and won't rev properly. I have replaced the fuel pressure regulator(it was leaky) and fuel filter, the TPS, and I put a new timing chain on because I thought maybe it had jumped a tooth or two. But the problem still exists. However, if I disconnect the vacuum line from the MAP sensor the vehicle will idle and rev in neutral, but won't rev correctly under load. I'm going crazy trying to figure it out. Please help, especially if you have had the same problem.

Mark

Tuffdrvr88
02-10-2006, 11:59 PM
Do you have working lights when the car dies out? Will it crank right away? Does the car make any noises when stalling? Do you have an OBD I connector under the dash that you could pull codes from?

2000CAYukon
02-11-2006, 12:31 AM
I have an '88 suburban, 350, 4x4, auto, 1/2 ton. It suddenly died one night while I was turning a corner. Since, it won't idle and won't rev properly. I have replaced the fuel pressure regulator(it was leaky) and fuel filter, the TPS, and I put a new timing chain on because I thought maybe it had jumped a tooth or two. But the problem still exists. However, if I disconnect the vacuum line from the MAP sensor the vehicle will idle and rev in neutral, but won't rev correctly under load. I'm going crazy trying to figure it out. Please help, especially if you have had the same problem.

Mark

The job of the MAP is to detect load so that explains why it won't rev correctly under load. If you have a vacuum gauge, you can test it to see if it holds a vacuum (it should, else replace). Even if it holds vacuum, it can be off.

Depending on your altitude, the voltage from the map should be 3.8 to 5.5 Volts (igniton on, engine off). Engine on at idle, it should be around 1.7 to 2.2 Volts. You will need to back probe if you don't have a scan tool. Also check the vacuum hose for any damage.

Recently on my 90 K1500, I replaced the timing chain (it was loose!) but it still was not the same. My car uses the same MAP so I swapped them and it ran much better and I am much happier now with the way it runs.

The other thing to check for is a restricted exhaust.

//2000CAYukon

The Barmy Scotsman
02-11-2006, 03:05 PM
I actually tried a new MAP sensor on it, and replaced the vacuum line to it, neither of which helped.

2000CAYukon
02-11-2006, 03:09 PM
I actually tried a new MAP sensor on it, and replaced the vacuum line to it, neither of which helped.

OK. Have you check fuel pressure? I know it is a pain on the TBI engine since there is no service port but you need 9 - 13 PSI to run right.

On my 90 K1500 pickup, it died going around a corner and it was the MSD coil that I had installed a year earlier. In my case, I had no spark at all after it died.

//2000CAYukon

The Barmy Scotsman
02-11-2006, 03:59 PM
If it was fuel pressure, do you think it would be affected by disconnecting the vacuum line on the map sensor? If I disconnect any other vacuum line it does not give the same effect.

2000CAYukon
02-12-2006, 12:54 AM
If it was fuel pressure, do you think it would be affected by disconnecting the vacuum line on the map sensor? If I disconnect any other vacuum line it does not give the same effect.

Yes. When you disconnect the vacuum line to the MAP, the PCM "thinks" that the engine is under load and will add more fuel.

If the fuel pressure was low, pulling the vacuum line may give it enough fuel to run but there is still not enough fuel to run the engine under a real load.

On my 90, if I pull the vacuum line on the MAP, the engine will stall.

//2000CAYukon

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