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Ok guys, been banging my head against the wall on this one. Truck was running great, went down with a leaking intake manifold. Here's what I did, replaced head gaskets, all manifold gaskets and o rings, put a new distributor on as the old one was cracked. Egr delete kit, new plugs and wires. Adjusted valves.
Truck now has a random but pretty persistent misfire that can be seen on all cylinders with a scanner, doesnt donit when idling.
Tests i have done..1. fuel pressure Is at 55 psi running, doesnt hold with key off though. Pulled upper intake and see no fuel.leaking by regulator or inectors.
2. Vacuum test was 20 in hg steady at idle. Perfect
3. All cylinders 160 psi +/- 2 compression
4. Maf only reading 1.0 g/s on scanner
5. Map only reading 9.4 inhg on scanner
6. O2 sensor bank 2 sensor 2 set code for high voltage. Reading 1.1v
7. Smoke tested for vacuum leak and found nothing
8. Cmp retard is at 1.0° (within spec)
9. Timing advance is roughly at -33
Only other code it shows is insufficient egr, which inhave ordered a new tube, but not sure how that could relate to low MAF and MAP readings.
The misfires themselves dont even create a check engine but i can feel them and count them on my scanner
What does the upstream 02 ready? Does upstream and downstream agree? The high voltage is very likely from the EGR delete and I would think you’re best bet would be to take it to a tuner.
MAF is WAAAAAY low. Disconnect it just and see what happens. Default strategy might be better than an under reporting MAF.
MAP is also low.
I know you said you checked for vacuum leaks but this makes me lean toward a vacuum leak. I don’t think it would be an air intake restriction from your vacuum gauge readings. Have you checked PCV?
Making Pressure Differential Sensors (PDA Sensors) for pressure pulse diagnostics.
Currently servicing Central Texas.
I did do a smoke test for a vacuum leak, and didn't find anything. I do however hear something hissing around where the pcv connects to Intake. But I've sprayed it and everything and i cant find it still..
The MAF AND MAP readings dont change much above an idle, the maf goes to 2 g/s max which is will low, cmp readings were done at 1000 rpm. O2 sensor voltage goes up with rpm as well. Not sure how old the spider is, but it doesnt leak at the regulator or the injectors. Tested that with the upper intake off and cycling power on
One problem with the poppets in spider,the older they get,clogged,bad spray pattern,the fuel pressure needs to be on the high side,domino effect,are the front 02's switching wildly?and what bank is worse
So after having the upper plenum off to check for spider fuel leaks, I re installed everything, didn't change any parts and now my misfire is in cylinders 4 and 8 only, instead of a few misfores across all cylinders
