1998 Suburban misfire under load
 

I just got this Suburban. It is a 98 5.7 with 140,000 miles. The test drive was great and 3 days later the 30 mile drive home went well.
The problem is I think the drive home went well. The "cruising at 55" miss is very hard to feel so I'm really not sure if it was doing it on the way home or not.

Did have a light on for O2 sensor when I got it.

2 days later, i decide to clean the engine. I sprayed Gunk on the valve covers and below. I did not come up any higher. I used a very light spray of water to wash everything off. A little later I drove it and could feel the miss/skip.

1. When cranking you turn the key and you get 1 turn then slight delay and turns again then cranks. "kind of like a weak battery" Battery is 4 years old.

2. In park rev up to 2500-3000 rpms you can feel the miss

3. Driving down the road when you get to a cruising speed you just can feel the miss. Drop a gear so it revs up more and the miss is much
more prominent. Did that 1 time and ended up with a 0300 random cylinder misfire code



The guy I got it from claims to had the fuel spider replaced with the upgraded MPI unit. I can tell the intake was removed so I have no choice but to believe him. He also claims to have had the oil pressure sending unit trying to stop the oil leak the suburban does have. He also said the fuel pump was replaced. All of this was earlier this year.

I have not attacked this in a smart manner. I have replaced the cap, rotor, plugs, wires, ignition coil, and throttle position sensor with AC Delco parts. Also replaced the O2 sensor.
Still happening but O2 sensor code has not returned.

I checked fuel pressure

58psi with key on
49/50 with engine running
key off - does not leak down immediately waited a couple of minutes and it had not leaked down at all

From reading here and on the net I have several more things to try but I don't want to throw darts and the board.
1. knock sensor
2. crank position sensor
3. clogged cats maybe?

My scan tool is basic and does not let me look at cam retard so I have no way to check timing.

Any suggestions? I am really leaning towards timing at this point. At 140,000 miles should I
try to replace the water pump and timing chain? I am really starting to feel lost here. I also need to
try to figure out the oil leak. The oil is coming down the rear of the motor, not much maybe a couple of
drops a night.

I noticed it only runs about 170 degrees according to the dash gauge so I replaced the thermostat with a new 195. No change the temp still runs around 170. I then changed the coolant temp sensor and now it runs at 240/250. I am not loosing coolant/water so I really doubt its really running that hot. I have no way to check though.

I am now pulling my hair out.

The distirbutor gears wear in these and can cause miss fires you have to pull it to inspect and get the cam retard set again either by buying a scanner or finding someone with one,after getting my burb i got a scanner that reads real time data and cam retard its an AutoXray 6000 got it on ebay for $100 it almost a must on these newer cars,if i wash my engine it will kick back when trying to start unless i dry the inside of the distributor cap off,you should be able to see if he upgraded the spider by looking down thru the throttle body over toward the #1 cyl area the old unit has really thin lines and the new ones are bigger in dia and have black plastic sleeve over a white fuel line with 2 wires running out to the fuel injector

So if pull the distributor out to inspect it I will have to get the cam retard set again?
I have done a search for the Xray 6000 but they are currently $300. I have spent
alot of money very quickly and am going to have to slow down for a little while.

I also struck out with knowing anyone with a scan tool.

I will check and see what I can see through the throttle body later today.
Thanks

My '99 Burb had same problem. Cause: Dist. has a vent at bottom of housing, water/condensation go in rise to top of cap, corrode cap pins. As you have replaced all those parts already, recheck inside of dist. cap for signs of corrosion/wetness. This could being causing the spark to "blow out" under load. Hope this helps.

Ok so I removed the dist tonight and 6 of the teeth are almost as sharp as a knife and the rest of them look good so I will replace the dist and go from there.

At least I finally found a part that shows definite wear.

They carry all metal distributors on Ebay one has a 5 year warrenty i'm replacing mine with that because my screw holes for the cap are cracking,you should be able to set everything a TDC mark it and pull it out and change it and put it back together and be close on the cam retard keep searching Ebay for scanners thats where i got mine

Changed out the distributor. It started right up and it running much better.
It is throwing the P1345 code so I need to make some fine adjustments. I hope my friend comes up with the scan tool he thinks he can get.

Did you ever find the answer to your problems... Let me know... Brad

It was worn teeth on the distributor. Once I replaced it and got the timing set everything was good

So you replaced the while distributor or just the top upper part ?