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Author Topic: Idle sounds like diesel after revving up and then letting off throttle...help!  (Read 2855 times)

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Offline Basher13

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I have a 2.3 out of a 74 ford pinto.....has points distrib and motorcraft carb.  Idles great at start up.  push throttle down and sounds great all the way up to slamming throttle down to hit top end.  however, after letting off of throttle and rpms drop back down it idles like a diesel tractor and if you give it gas it just cuts out.  If you let it idle like that for 15-20 it cleans up and idles good again.....i have replaced every electronic part there is....rotor, cap, distrib, coil, coil wire, plugs, wires, etc. etc. i see no apparent vacuum leakes.  spray ether around intake and carb and there is no change.  Any other ideas?

75bobcatv6

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have you rebuilt the carb? not 100% but sounds like something internal with the carb.

Offline oldkayaker

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Another possibility is that during the pedal floored event, the rpm is increased high enough to cause the hydraulic lifters to pump up and hold the valves slightly open.  When the rpm is reduced, the lifters bleed back down after a few seconds allowing the valves to fully close again.
Jerry J - Jupiter, Florida

Offline Pinturbo75

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x2, sounds like weak springs....
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Offline Pintosopher

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The 74 2.3L had lubrication issues with the Lifters, and it will score that cam bad when the Chattering begins. Replace all the lifters, and make sure the rockers and cam lobes aren't toast already. This occurs on high mileage motors or ones that have neglected service oil change issues. Good luck!
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Offline Basher13

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Just an update and more info. Everything electronic and fuel related has been checked. Compression is equally good in all 4 cylinders. This motor has had work done to it. Head work, afyermarket lifters, springs, etc. It measure 180 compression in all 4. Idlea and winds out like a beast then let off and it disels and dies or just diesels for 20 seconds. If u hit the gas during this dieseling it just cuts out. Wait 20 seconds and it runs good again.

Offline Basher13

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Forgot to mention it has comp cam. Lobes all look fine

Offline Pinturbo75

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and again,,, that is a symptom of weak valve springs...
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73 turbo pinto panel wagon, ms1, 85 lb inj, fmic, holset hy35, 3" exhaust, msd, bov,

Offline r4pinto

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Have you taken a look at the internals like the cam, lifters & springs? There could very well be a mechanical issue causing your problem. Especially since like Pintosopher & Pinturbo75 have said they are known for some mechanical problems.
Matt Manter
1977 Pinto sedan- Named Harold II after the first Pinto(Harold) owned by my mom. R.I.P mom- 1980 parts provider & money machine for anything that won't fit the 80
1980 Pinto Runabout- work in progress

Offline racer99

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Sounds like its way fat after you let off the gas.

Internal carb issue,I think.
Look down in the carb bores while its running
like crap and see if there is excessive fuel .

After whatever the problem is it clears itself up after 15-20
seconds,sounds like fuel delivery.

Might want to change plugs after you find the problem.

Offline Pintosopher

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After careful analysis of the symptoms and consequences, I'm inclined to agree with Racer 99. The cam inspection was to verify condition of the followers and lifters. Yours are showing no wear, so unless a Oil pressure gauge reveals very erratic oil pressure that coincides with the dieseling and starving out, I doubt that the lifters, springs , or valves are the issue.
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Offline Basher13

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Once again, not a carb issue. Have tried a holley 350 with big jets and small jets, also tried a good stock motorcraft.... tried esslinger intake and stick intake....trie d good manual fuel pump and two different electric fuel pumps.... Tried brand new gas....differe nt fuel line....(this is a race car)...all ended up with same results

Offline Pintosopher

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After thinking further about the symptoms, I wonder about the Headwork done to the engine. If all the other swaps had no effect, there is a chance that the mods to the head are causing Fuel dropout in the intake just ahead of the intake valves. Also the finish for the ports should be a lightly brushed texture on the intake side. No mirror finish on that side of the head (exhaust only). A vacuum reading should also show a wildly swinging gauge if the Fuel dropout is occurring. And wet plugs might be evident too. Just another possibility.. ???
Yes, it is possible to study and become a master of Pintosophy.. Not a religion , nothing less than a life quest for non conformity and rational thought. What Horse did you ride in on?

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