SD TPI bucking/sputtering under moderate to heavy acceleration - Third Generation F-Body Message Boards

1986Z28OWNER · 07-27-2009, 02:37 AM

OK, here is the problem i am having, Once the car has reached operating temp, it develops a very severe hesitation/buck/sputtering condition on moderate to heavy acc. in any gear. Here is some info in the car, it is a 1991 Z28, 350 tpi, 5 SPD, engine has about 3000 miles on it, and this condition only developed about 7-800 miles into driving the car. The car is lightly modified, Eagle rotating assembly, flat top pistons. Stock 083 350 tpi heads(gasket matched) with upgraded valve springs and retainers(comp cams rec springs). The cam is a comp cams 262H-R12, the specs are as follows 206 int./210 exh @ 0.050", 0.450 int./0.480 exh. lift, and a 112 LSA. The TPI is all fairly stock minus a upgraded base(edelbrock hi-flow), Accel 24lb fuel injectors, an AFPR, and a TB airfoil. The engine also uses a MSD 8366 billet distributor, comp cams roller tip rocker arms, hooker 2450 headers, matching Y-pipe, and a flowmaster cat back. All the sensors were repalced on the car with either standard or AC Delco replacments.

The car set a code 34(low MAP sensor voltage) so I swapped the MAP sensor(a standard brand one) for a OE GM sensor, and took it for a drive. At first the car seemed great once it had reached operating temp, and showed no issues untill about 10 minutes later until it developed the same issue with about the same severity. This is really frustrating, and id really like to get this problem fixed so i can actually enjoy this car somewhat this year, but in it current state, it runs like a POS

Any help is greatly appreciated.

1986Z28OWNER · 07-27-2009, 02:48 AM

also i should mention, that we had this exact combo in a buddys car, cam heads and all(i even used his PROM) and the car ran awesome. I should also mention that EGR was also disabled(although not from the PROM) to see if it was causing the issue, it is not

C-Titan · 08-22-2009, 10:18 PM

ever find a solution to this problem??

1986Z28OWNER · 08-22-2009, 11:08 PM

Quote:

Originally Posted by C-Titan

ever find a solution to this problem??

not 100% yet, i found a very large vaccum leak, and i am replacing the intake manifold gaskets tommorow, i am hoping this fixes the problem, im pretty sure it will, if it dosnt, the car is getting parked and the engine is coming out(its coming out at the end of the year anyways, to check it over,a nd swap to a bigger cam and some vortec heads)

C-Titan · 08-23-2009, 12:49 AM

let me know how that goes... i just started having the same issue today out of no were, i thought i bought some bad gas... a vacuum leak does sound plausible tho...

rx8ss · 08-24-2009, 10:38 AM

Check fuel pressure while driving to make sure it does not drop. I am having the same problem, checked my fuel pressure while driving and it dropped worse as it got warmer.

dmanella · 11-03-2009, 03:29 PM

I am having the same issue. Replaced Dist, wires, and plugs. It is less noticeable after the plugs and wires were replaced but still present. I happens at around 2000 RPM to 2500 RPM. I think it is the fuel pump.

Thanks

C-Titan · 11-03-2009, 04:05 PM

Mine turned out to be a problem with one of my MSD wires... Hair-line split was causing it to arc on the block...

1986Z28OWNER · 11-03-2009, 07:48 PM

The problem for me was a big vaccum leak caused by a pinched injector O-ring, and a bad seal with my stock runners to a edelbrock plenum. i guess when it was cold it sealed the vaccum leak.

dirtyd6669 · 11-08-2009, 04:56 PM

after ur car got to operating temp and u guys were having this problem did it take forever to accel even if u had the gass all the way down