• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Tips
Tips

Wedge TR7 Engine Problem

Share this page

johnrip

johnrip

Jedi Hopeful
Country flag
Offline
My 1980 TR7 engine was running great. The next morning it is sputtering, backfiring and bogging. My mechanic said that it was running on two cylinders, 3 and 4 were low compression. When he rechecked, compression was low on 2nd, but not 3 and 4. Any ideas???Could the carbs be washing out a cylinder?What would make compression change so? Do I need a new mechanic?
 
I get several other opinions, but is doedn't sound right to me that the compression woudl suddenly change like that. Suggests the measurements were not done properly.

Generally speaking you want to start with the ignition systems first, then move to fuel.

Is she getting OK spark? Coil, points (assuming she has points and not an electronic ignition), and condensor all OK.

Fuel filter and pump OK?

Oil in the carb dashpot?
 
I probably can't add anything of value except to agree with what's been said. You might put some oil in each cylinder and check comp again. Might shed some light on the situation. If it was valves way out of adjustment they might improve if the engine was up to operating temp as it was when it last ran well. The suddeness with which it went funky makes me think it must be something simple like plug wires coming loose or moisture getting into something. The distributor cap clips on mine are a pain, and sometimes come adrift when I think they're secure. Dashpots are a definate check item as noted by tdskip. Do take care and thanks for letting me go on.
 
johnrip said:
Do I need a new mechanic?
Click to expand...
I would sure want to have someone else check the compression (like yourself)! While what he reported is not impossible; his making a mistake is the most likely explanation, IMO. The only other explanation I can think of would involve multiple valves that decided to stick and then unstick.
 
I would start with the ignition too. Check all the wires, distributor cap and rotor, pull the plugs. If you have the Delco electronic ignition, pull the module and take it to Autozone and get it tested for free (put a good layer of thermal grease on it when reinstalling).
 
Maybe your mechanic isn't up to date on diagnosis. All he/she had to do was install an oscilloscope and low compression would show up as low KV demand for the affected cylinder. Also the scope tells all but a very few tales about what is happenning inside the engine. BTW, I'm an ASE Master, L-1 Advanced Engine Performance certified.... with 33 years under my belt. A lot of guys just do not have expensive diagnostic tools at their disposal.... but if you went to a professional, they should. It isn't very likely to be a mechanical issue unless you broke a rocker arm or such.
You must get back to basics... fuel and ignition must be exonerated first.
 
Back
Top