1981 Elco 305 - 2 cylinders not firing



Feb 8, 2018
Houston, TX
Been having this elcamino for about 2 years but i never went in depth with it why i ran like crap. Popping out the carb at high speeds. So recently i made time to look at it (blame it on the covid19)

Went around pulling plugs 1 by 1 to see if they would all make the engine bog down. #1 and #7 seem to have no change when pulling the wires off. Swapped wires and plugs around to see if the problem shifted to a different cylinder but it remained at #1 and #7.

Did a dry and wet co pression test on those two cylinders plus a good cylinder (#2) to see what the differences would be. Here are the results.

#1 dry:50psi wet:60psi
#7 dry:90psi wet:105psi
#2 dry 135psi wet:150psi

Is there something i can try before removing the head to see exactly what's going on with it? Here's what I've done in the past week with it;

Started off by changing intake gasket because it was suspect (i previously had used the plastic strips the gasket kit comes with)

Adjusted valves while intake was off (each cylinder at tdc, tighten until 0 lash, then 1/2 turn more)

After doing the dry/wet co pression tests i took a hammer and a block of wood and tapped on the valves (removed rocker arm for this, then adjusted valve with engine running)

Exhaust does not smoke at all. Engine oil does not look like chocolate milk.

Thanks guys, hopefully you guys can point me to what to do next.


Rocket Powered Basset Hound
Jul 24, 2009
Socialist NY
Check your valve springs you may have a crack one or two.

If not, may be a head gasket or get ready for a rebuild
  • Like
Reactions: 83MonteCarloSS
Clone TIE Pilot

Clone TIE Pilot

Royal Smart Person
Aug 14, 2011
Galaxy far far away
Could simply be sticky valves. Valves that are slow to close behave similar to late cam timing and can cause lack of compression. Run some MMO in the crank case to see if it improves.


Feb 8, 2018
Houston, TX
Could simply be sticky valves. Valves that are slow to close behave similar to late cam timing and can cause lack of compression. Run some MMO in the crank case to see if it improves.
Definitely will do that. Will i need an oil change after?


Nov 15, 2014
Des Moines, Iowa
Definitely will do that. Will i need an oil change after?
Yes. Add Marvel mystery oil.
Let idle. Blip throttle a few times. Let cool. Drain and cut open filter. Glitter is bad. If no shiny bits put good conventional oil with a zddp additive and see if it's better. Do this after inspecting for any obvious broken things of course.
  • Like
Reactions: RustBucket


Royal Smart Person
Oct 2, 2016
Does it pop through the carb when you rev the engine in park or neutral?

oldsmobile joe

Royal Smart Person
Nov 12, 2015
after performing a compression test, and finding low compression. the next step in diagnosing your concern is to perform a cylinder leak down test to determine where the compression is going.
popping back through the carb usually indicates valve train issues, burned valves, sticky valve stems or lifters. while flat cam would give low compression, it would not cause popping back.
mmo or gm crank case cleaner may clean up the rings and give better compression, it would not address the popping back. it may help with sticking lifters depending on where the lifters are sticking.
adding zinc at this point would be a waste of money.
Thread starter Similar threads Forum Replies Date
C ISO a 1978-1981 Malibu 2 door G-Body Cars for Sale / Trade 1
P Need help decoding a 1981 Malibu body tag General Discussion 1
P 1980/1981 Pontiac Wiper Switch w/Delay Wanted 0
19Monte81 1981 monte carlo New Users 4
55Belairman 1981 Malibu parts for sale G-Body Parts For Sale / Trade 0
butch2427 my new project, 1981 Malibu 9C1 New Users 16
442kid 1981-1988 monte carlo SS black side Qtr Glass windows G-Body Parts For Sale / Trade 1
D 1981 Buick Regal -Starts but majorly misfiring- Electrical / Ignition / Starting 34
P 1981 LeMans front end G-Body Parts For Sale / Trade 2
08Malibu MALIBU Looking for 1981 Clear corner lenses Chevrolet Monte Carlo / SS / Malibu 10
Regalman08 FOR SALE More parts added 1981 Malibu classic 2door parts G-Body Parts For Sale / Trade 12
J Late Model Chevy Truck Heads (1998) on a 1981 305 block? How-To's / Knowledge Base 11
9 1981 Grand Prix lj v6 no start Pontiac Grand Prix/Grand Am/LeMans/Bonneville 68
O Wanted 1981 Olds Cutlass front license plate holder Oldsmobile Cutlass / 442 / Hurst/Olds 0
81MalibuMan Rear door panel removal in an 81' Malibu New Users 6
K 1981.pontiac lemans engine swap Engine / Swaps / Driveability 30
M Rough Idle 267 4.4L V8 General Discussion 6
P 1981 Pontiac Grand LeMans Safari Wagon G-Body Build Threads 44
M MONTE CARLO 1981 2 Door Landau New Users 1
69hurstolds CUTLASS 1981 Factory Turbo Cutlass 2 door?? Oldsmobile Cutlass / 442 / Hurst/Olds 19
SSpev My 1981 wagon Wagons! 3
8 1981 t top build Oldsmobile Cutlass / 442 / Hurst/Olds 2
S In desparate need of a passenger front wheel well moulding/trim w/2 tone paint for my 85 ElCo Wanted 3
Crd80BU 200-4r rebuild 1986 MC SS in a Elco Transmission / Rear End / Driveline 31
Carlos Garcia Back in action. Body / Trim / Paint / Glass 12
T 85 elco colum length Frame / Chassis / Suspension / Steering 0
D Elco 300 Utility Wagon G-Body Build Threads 56
V Elco Seats won't slide Interior 4
RustBucket Exhaust 305 Exhaust 8
8 CUTLASS 84 supreme 305 swap (need help) Engine / Swaps / Driveability 27
J MONTE CARLO Installing b&m automatic shifter knob Chevrolet Monte Carlo / SS / Malibu 0
C 78 Cutlass factory 305 to 71 455 olds Engine / Swaps / Driveability 35
4 EL CAMINO 350/290 swap from 305 Fuel / Air / Boost / Emissions 0
J Late model 305 Chevy Truck heads on one of our 305? (mine is an 81 Monte) How-To's / Knowledge Base 8
W I have my grand mothers 1984 Monte with cloth landau 305 ac and wire wheels approx 54000 miles General Discussion 122
malibu79 305(LG4) valve stem seals Engine / Swaps / Driveability 35
H Turned key and got NOTHING! 1983 Grand prix 305 Electrical / Ignition / Starting 10
hangar401 305 Exhaust mod Exhaust 12
K Is the 88 lg4 305 a roller cam motor or flat tappet cam?? Engine / Swaps / Driveability 2
malibu79 305 LG4 overcooling? General Discussion 7
J 83 cutlass 305 with factory gauges- temp sender Electrical / Ignition / Starting 0
84cutspreme CUTLASS Factory 305 cutlass Oldsmobile Cutlass / 442 / Hurst/Olds 4
R Sbc 305 build with factoey bottom end Engine / Swaps / Driveability 36
I CA Smog Test/Replace Electronic Quadrajet Fuel / Air / Boost / Emissions 5
S 305 won’t turn off General Discussion 3
Gonzo1970 E4ME off of a Chevy 305 Fuel / Air / Boost / Emissions 4
M 305 hesitation/miss-fire Electrical / Ignition / Starting 13
Similar threads

Please support GBodyForum Sponsors

Classic Truck ConsolesDixie Restoration DepotMike's MontesP-S-TSouthside Machine PerformanceUMI Performance

contact[email protected]for info on becoming a sponsor