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Help with problems
Experiencing a problem and looking for suggestions as to what it might be:
- Problem started with a slight hesitation when first stepping on gas from a stop. Occassionally, a loud backfire as it is getting underway - always from driver's side. - Problem got progressively worse and car won't idle. Smooths out at about 1500 RPMs. Backfire from driver's side more frequent. While underway, car runs just fine. Setup: 427 side-oiler, Edelbrock Performer RPM heads and intake, Holley carb with vacuum secondaries, MSD ignition, coil and distributor. Thanks for any help. Kevin |
Sounds like it's sucking air on the drivers side bank..
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Primary accelerator pump may not be kicking in early enough, possible the primary float is too low, lastly I'd check for a possible break in a driver side plug wire. Probably it's the accelerator pump
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Don't ignore a torn diaphragm (power valve) on the primary side of the carb. Loads up off idle (too much fuel) and can cause severe hesitation and/or a backfire. Once underway the engine is able to burn off the excess fuel that the torn PV is causing.
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Thanks for the input. The car has 5,300 miles on it - haven't had the head and intake bolts re-torqued so if it is sucking air, maybe that is the problem. Good place to start. Will check the other suggestions as well.
Thanks, Kevin |
Kevin,
I know it sounds obvious, but I would first verify the basics, like timing, cap/rotor inspection, fuel pressure, and plug condition. See what those tell you. If you are backfiring it could be a timing issue. If it is a carb issue, it would likely show up on the plugs. |
Before you do any heavy lifting; blow out the idle air bleeds (the ones farthest from the middle of the carb) with some carb cleaner. Be careful, wear eye protection and wrap a rag around the bleed to prevent splash back.
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Kevin - I second Lippy's advice. Is it backfiring through the exhaust or the carb - sounds like through the exhaust? If you run it again see if the carb boosters are dripping any fuel into the running engine. I was working on one of my carbs lately and managed to get the secondary float to hang up and it was dripping fuel out the boosters and causing a rough idle and odd exhaust note. As noted by others a leaking intake manifold is all too common with these motors - should be apparent from the plugs. Sometimes an external intake leak can be traced with propane torch gas - but if the leak is internal to the engine it won't work. Good luck tracking the problem.
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If you do have a leaking intake gasket (not saying you do), retorquing it won't help. Once they start leaking, they won't stop. But I would check the basics very thoroughly first. It could be something simple and easy.
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Thanks for the help and advice. I'm leaving for a week long business trip tomorrow so it will have to wait. I'll check the basic things first - good advice. As for retorquing, even if that isn't the problem, from what I've read the bolts have a tendency to come lose and it should have been done earlier anyway.
Kevin |
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Did the bolts that hold the carb to the intake loosen? Is there a fuel drip from the carb to the intake (exterior staining)? Did you have a backfire through the carb that could have blown out the power valve? Which MSD ignition set up do you have? (be specific) MSD Box? MSD Distributor? MSD Coil? Bill S. PS: Backfire on deceleration, if so, tighten your header bolts. |
Hi Bill,
Thanks for the suggestions. Yes, it is an MSD 6al, MSD distributor 8594 and MSD coil 8222. The backfire occurs when first accelerating from a stop - the engine runs rough for a couple seconds and it is during this time that it sometimes backfires loudly through the exhaust - always driver's side. Once the engine smooths out after about 2 - 3 seconds it runs fine and continues to run fine until returning to idle again. I put a new dist. cap on, although the original was still in good shape - I've cleaned the cap contacts and rotor regularly and coat with dielectric grease. Will start checking all the above. Thanks again, Kevin |
Thought I'd post the resolution to the problem - turns out it was the coil. The car is running strong again. Thanks for all the suggestions, much appreciated.
Kevin |
Fairly common. MSD is not what they used to be like.
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Stay warm. Dan |
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Initially, yes - it idled fine until it got warm and then wouldn't idle at all. Even hot it would run fine at higher RPMs and driving the car felt normal until returning to idle. As the problem progressed, it wouldn't idle even when cold. So, the mystery to me is how it ran well at speed but not at idle. Regardless, glad to have it running well again. Kevin |
I finally got a chance to go through my receipts and found that the coil was purchased last September - about two months out of warranty. I called MSD and told them when I purchased it and mentioned that the engine wasn't installed in the car until December. I don't think I even needed to mention that because he had no problem giving me an RMA number to replace the coil. Didn't ask for a copy of my receipt either so just took my word for it. I do have to ship the bad coil back to them, but no big deal.
So, I read lots of MSD bashing and I won't argue about the reliability of their stuff, but their customer service scores some points with me - they did the right thing. Kevin |
Kevins,
That is great that you found the problem and it was something simple and they will replace the coil. I don't know about MSD as I haven't had to replace anything on mine, but I run the Jacobs Pro Street on my Cobra and when I found the coil was faulty the sent me a new one and asked for the old one back as they wanted to look at it. Then about a week later I got another coil and a letter telling me to throw the one they had sent away and the one that just came would fix the problem. When they tested them it turned out the coils they sent out with the Pro Street Ignition couldn't take the voltage it put out and they would actuality arc from the output terminal to the case which was grounded. They then sent new coils to all people who had the Pro Street, so you may have to send the old coil back to them so they can look at it and see what happened. Ron |
Couple of questions
Kevin2 MSD does stand behind their products for multi reasons. They also want the bad parts back for R&D. I don't know which coil you are running. I have to ask you about how the coil is mounted and if it's a oil filled old style design? Mounting oil filled can and will over time, horizontial on a motor will go bad. Vibration heats the oil in the canister and turns it to foam and the heat can cause an explosion. I have blown 2 on my CJ. I know it's not the original way or location. Also only the lower half of the coils are being cooled by the oil and the upper windings are being cooked. Last coil I blew had the dry coil windings blue and black and the lower part of the coil was clean coated windings. Gald the car is fixed Rick
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