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Topic
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Dirt Mongers,
Truck seems to mostly run fine except at hard acceleration. Hesitates for maybe 1/2 second & struggles a bit to catch up. With the doghouse off I can hear a short burst of sucking. Sounds like it’s coming from the throttle.
So far:
No codes.
New cap, rotor, plugs. Air cleaner.
Swapped MAF with a spare. No change.
Found timing chain pretty loose. Replaced. Attempted relearn procedure. Don’t think I’m doing it right. No related code. Issue was present before timing chain.
Found CMP Retard timing a few degrees off (-5). Adjusted to 0 (RPM > 1000)
Distributor has some end play which I thought BINGO!, but new unit in store has comparable end play? As well as others I look at when @ the junk yard.
New Fuel filter.
Fuel pressure primes @ 60 psi drops to @ 55 psi. On hard acceleration spikes to 60+
Watched Eric’s excellent review video of vacuum diagnostics. And ran through all his tests.
Steady 18.5 – 19.5 vacuum and diagnostic all seems normal. Hard acceleration vacuum drops to 0.
Ran through EGR diagnostic. Check.
Fuel trims were a little wacky till I put fresh gas in.
O2B1S1 Seems a bit sluggish and heater may have only just failed.
Issue is present with no difference whether fuel system is in open loop or closed loop.
Kicked the tires and swore loudly.I could sure use some new direction.
Thanx!
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Clean the MAF sensor properly. Mine was doing the same thing and cleaning the MAF fixed that issue but I have others. Don’t use Brake Clean or Carburetor cleaner. I cleaned mine with a Q-Tip (Bent to reach and very very gently) and alcohol. Lots of black stuff came off the sensor. How do your fuel trims look? Mine are too high and am getting lean codes.
Silly thought, but have you checked the tranny fluid?
How many ignition coils does your engine have? If it is multiple coils, try unhooking one plug wire at a time to see if that changes anything. If it doesn’t, then it may be a faulty coil. Careful of that coil voltage when its running, very dangerous!
Thanx,
@Jonmon1 Cleaned MAF with MAF cleaner and Swapped MAF with a spare. No change.
Fuel trims were a little wacky till I put fresh gas in.
@peshewa 1 ignition coil. Diagnostic procedure basically says either it works or it doesn’tUPDATE:
TPS – Throttle position sensor tested by monitoring voltage output. No trouble with full range of motion ( .6v – 4.5v )
Neglected to mention thoroughly cleaned throttle body some time ago.These model year trucks/vans have the terrible spider fuel injection unit.
The way they work is there is 8 injectors in the middle of the intake manifold (Underneath it inside the plenum) which have fuel lines which run to individual poppet valves at each cylinder intake valve. These are known for sticking and causing bad idle or fuel starvation during acceleration.
You said fuel pressure was fine so we can rule out a bad regulator and pump but the poppet valves themselves get carbon build up which may impede fuel flow to some cylinders. Does it idle ok? Does it only hesitate when there is a load on the engine?
Now its not the easiest part to replace because like I said, its inside the intake plenum (thanks GM). You can get a multiport conversion kit for like 300$ on amazon made by the OEM AC Delco. These not only improve throttle response but are also a lot more reliable because the injectors are actually farther up the intake valve runner and don’t have poppet valves any more so they don’t get carbon build up and clog.
I’ve done this on a friends truck before and it takes about an hour if you know what you’re doing. If you do plan on doing this and need any help you can message me or look up a youtube video on how to do it.
@Oddball0045 Idles ok. Only hesitates on acceleration or even punching the throttle while parked. Also ok if I bring up the RPMs slowly. Not at all worried about this sort of job. I just can’t get past that sucking burst when I do throttle up. But I have run out of any other ideas. My chevy & Jimmy both have the 4.3 so I’m familiar. Ima thinkin might be worth a cheap try at a fuel cleaner. I never really used any of those products such as seafoam, so I don’t know how effective they really are. But, something in an effective cleaner seems cost effective before ripping in?
Thanx
I’ve only worked on the V8s but theV6 4.3 uses the same spider setup as the V8 engines (with two less injectors of course). Fuel cleaner may help if its only slightly gunked up just enough to make the poppet valve stick but more often than not these require new fuel injectors.
Lemme ask this. Has anyone ever encountered a vacuum leak that only leaks at higher RPMs/ vacuum? I notice the white locking tab on the spider harness plug is disconnected so someone has been in that neighborhood before for some reason. Can’t know if they were in the plenum and when I cleaned the throttle body it never occurred to me to peak inside and see if the spider is factory or not. I don’t think the replacements have those two black locking tabs on the poppets. What I’m getting at is the sucking burst comes from the throttle body area… or… the spider harness fuel island oring to the plenum. When I punch the throttle, vacuum gauge plummets like it’s supposed to and that sort of leak would not be detected. I know its a stretch but ima pretty stretched out ;]
Talking about Spider injection… Reminded me Eric’s good video with surprising vac leak right at the connector, caused by someone who’s been there.
so you might want to try what he did, just in case:
[video]https://www.youtube.com/watch?v=lAjbAzWQ0cw[/video]
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