Hard starting with a cold engine

Propane, Butane, LPG, GPL, C3H8, C4H10
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Frank
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Hard starting with a cold engine

Post by Frank »

I have a cold hard-starting problem with my 1977 Pontiac equipped with an Impco 425 mixer mounted on a Chev 350. The mixer is mounted on a Quadrajet throttle body and is supplied by a model E converter. The converter is equipped with a balance tube to the mixer and an Impco SV start assist valve. To minimize any chance of carburetor icing, I still have the OEM air cleaner’s hot air system connected except that the vacuum is controlled by the vacuum switch (on the thermostat housing), which formerly controlled the heat riser valve. The installation can be seen at: http://cars.rasoenterprises.com/Propane-77Pontiac.htm .

Lately, now that I have pulled it out of the field and am working on getting it road-worthy again, it is quite hard to start as it will not start with extensive cranking. Only by cracking open the throttle slightly will it start. However, by opening the throttle, I sometimes get an intake backfire. I checked the mixer’s gas valve diaphragm (black) and there doesn’t appear to be any holes. When it does start, the engine runs a bit rough until it warms up. When I tried adjusting the idle mixture, the engine seems to be fairly unresponsive to changes in the position of the screw.

I am suspecting that this problem might be caused by a vacuum leak at the carburetor base gasket. I was reading Impco’s service bulletin (24000 SERB-13) regarding idling problems with Rochester Quadrajet throttle bodies but didn’t find anything in it that mentioned cold hard-starting.

I don’t expect that cold hard-starting is normal for this application so I will be working on fixing it. I have been able to find another Impco service bulletin about Hard Starting (24000-22 SERB-22) that I will be using for troubleshooting.

Any advice would be appreciated.

Frank
Last edited by Frank on Thu Sep 15, 2005 5:28 pm, edited 1 time in total.

fordCourier

cold starting problems

Post by fordCourier »

I had a similar problem with my ford courier propane application. (140ci., CA125 mixer, Model "J" converter) Heres what I found:

1. The water hose routing was all wrong, sending the water back on itself (the Y-pipes were installed incorrectly.) The result was hard "hot" starting. As the hot coolant wasn't being adequately sent back to the block.

2. The convertor was contaminated by "heavy ends" or something like that. The W.C. port had been invaded by what lookeed like thin wheel-bearing grease. The rest of the convertor was similarly greasy. Solution: replace all moving parts and diaphragms with impco rebuilt kit. Took 1 hour. Clean parts with kerosene and Q-tips for the little passages. Dry completely. (If you're going this far you might as well rebuild the VFF-30 as well, its even easier.)

3. Installed SafeControls 5958 fuel-air controller. (O2 sensor and computer, AV-1447 rich feedback diaphragm in the mixer, and vacuum solenoid on the converter). More efficiency, more power, less emissions.

4. replace all loose/old vacuum lines. Test for leaks using heater hose as stethoscope.

5. Disconnect EGR as this will reduce volumetric efficiency of the fuel-air mixture (although increased cylinder temps are a theoretical possibility I haven't seen a difference). Similarly the hot-air intake will reduce volumetric efficiency as hot air will allow less fuel. I have deleted that as well.

6. Gap plugs to .028-.035. Cold starting takes more juice from the battery so inspect entire ignition and battery system. I have electronic ignition stock so I just replaced the Coil with Accel Super Coil, HEI coils are even better.

7. Set initial timing closer to 0 from stock, this is variable, you'll have to play around. The ignition is compromised by the stock distributor curve (for gasoline). If you can switch to mechanical advance instead of the stock vac. advance (get a racing application distributor that doesn't limit total advance) do it.

Hopefully a few clues that will help you out.

Frank
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Post by Frank »

Thanks for the advice.

From what I have found out, the backfiring is due to a problem(s?) in the ignition system. I have a new set of distributor cap, rotor, wires, and sparkplugs ready to install. I made sure that I got the cap with the brass terminals too. Also, I earlier upgraded my HEI coil to an Accel Supercoil. The plugs may have been gapped to 0.045" originally, but with all the miles from previous driving, who knows how big it is now. I'm going to set the new ones to 0.028".

I changed the spark advance curve earlier with lighter weights and springs. I'm not sure what the total advance is now but is another thing I will check. I think an advance limiter plate is still available from Gann but I haven't heard back from my supplier yet.

There is no heat to the intake manifold as I blocked off the cross-over passages and welded the heat riser valve into the open position. As for the hot air intake on the air cleaner, I have retained this to prevent carburetor icing. The vacuum supply is routed into the heat riser valve's vacuum switch so it shuts off when the engine reaches 180°F.

The mixer installed when did the conversion originally was pulled from a wreck so it may be worn out. Since the throttle is very sticky and the idle mixture screw barely turns, I think this will need some serious cleaning. I'll know better when I pull it apart to check it out.

Also, as the car was driven a lot (don't know exactly how much right now) since its conversion and the converter is horizontal, there is probably a fair accumulation of heavy ends in the converter. I'll clean it once I get the mixer off.

Also, the hard starting may be caused by a regulator leak. I will check it by taking the cover off of the converter and sucking on the vacuum line to the lockoff. If I hear a hiss, I'll know I have a leak there.

Anyway, I've been a bit tied up with getting my other winter car roadworthy again and building my new garage so I haven't been able to get to troubleshooting the starting problem on the Pontiac lately.

Gotta go. I'll post again with my progress.

Frank

Frank
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Fixed!

Post by Frank »

As I was checking over the various components in the propane system, I found that the problem was in the idle mixture system. I think that, while my brother was driving the car, someone tuned up the car and turned the idle mixture screw in until the spring was totally compressed (lean). It ran ok when warm but was very difficult to start cold. The fun part about it was that the screw was seized in the idle mixture cover. I had to pull it off the mixer and put some heat on it to loosen the screw. Before resorting to the torch, I ended up snapping off the screw head. Luckily, I found a spare in my parts bucket.

After reinstalling the idle mixture plate on the the engine, I started with the screw turned midway in. This time, the car was almost on the verge of starting and I knew I was on to something. Either the mixture was too lean or too rich so I took a chance and turned the screw out (richer). Engine was cranking over even more promisingly. I kept turning the screw out until it finally started. I let it run until fully warm and set the mixture to achieve the highest and steadiest idle speed, which was close to the screw being turned fully out. It now fires up from within a few seconds in below-freezing temperatures. Since my AC has lost some pressure (condenser's probably shot), I have also lost my fast idle when I set the heater to defrost. Within a minute, it will idle on its own anyway.

In the process of troubleshooting, I replaced the cap, rotor, wires, and spark plugs with Napa's premium parts. The old plugs were Motorcraft and were gapped to 0.045". I used R44TS AC Delco plugs, which are one heat range colder than the R45TS specified for the car on gasoline. I had experimented with spark plug gaps previously and never had any ignition problems even at 0.045". Rather than use the recommended 0.028", I compromised and gapped them to 0.035". With the fresh ignition parts, there is no backfiring when cranking with a partially open throttle.

I opened up the converter's top cover to clean it and discovered that there was minimal accumulation of heavy ends. After 86,000 miles, all I found was a very thin, waxy coating. I tested the lockoff valve by sucking on its vacuum supply hose and there was no hiss of fuel leakage in the converter. I disconnected the vacuum supply hose to the start assist valve and jumpered some power to it. With some more suction, I verified that this device is working properly too. After looking at the gas valve and its orifice, the wear of both seem minimal. The gas valve's diaphragm also seems to be in good shape too.

However, while running the car I noticed a metalic rattling sound that seemed to be coming from somewhere in the exhaust system. Some more examination revealed that it was the heat riser valve bouncing around. I should have removed it while I had the engine apart years ago but instead I just wired it open. The wire had fallen off and the valve was now extremely loose in its bushing. A few minutes with the cutting torch and the valve was finally gone. I tapped a 7/16" NF thread and screwed in a bolt. A bit of brazing and this will never cause me any problems ever again.

While the exhaust manifold was off, I noticed that my hot air stove was corroded and not positioned on the manifold to work properly. Before trying to weld it back on, I found that this part is still available from GM for C$10. I drilled out the rivets, screwed them down securely, and added a gear clamp for good measure. Now, carburetor icing during startups should never occur. This extra work must be what the military calls "mission creep".

I see that from my earlier work that I marked the harmonic damper with yellow paint to indicate total advance. This was because the timing tape I bought would never stay on properly. Now I just have to remember what those markings mean. Looks like I'll have to do some measuring and calculating to know for sure. I report my findings in my next post on this topic.

While operating moving the car around and I found that the stickiness has gone away so I'm going to quit while I'm ahead. Now, my next big job is to replace all three parking brake cables.

Frank

Frank
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Ignition Advance

Post by Frank »

I measured up the painted markings on the damper and I found that I had marked it for 28-32° and 40-46° of advance. I got these ranges from Storer's book and the first range is for mechanical advance and the second range is for mechanical plus vacuum advance.

Rather than use timing tape, which I could not properly install, the paint works just as well and is easy to see on this engine. The idea is that once the advance is all in, depending upon whether the vacuum advance is connected, one of the painted marks should be at the 0° mark on the scale.

I found that my vacuum advance does not seem to be working at all and that the mechanical advance springs are very weak so that the total centrifugal advance is something like 20°. It looks like I'll be investing in an advance kit like Accel's #6011. With luck, this should make a big difference in my fuel consumption.

BTW, my front parking brake cable was still good but in the process of putting everything back together, I discovered that the brake shop my brother used last did a major screw up. Besides losing the thrust washers on the self adjusters, they installed a right-hand spring on the left-hand self adjuster. Luckily, I finally was able to use some spare brake parts that I've been hanging onto for 20 years.

Frank

fordCourier

Re: Ignition Advance

Post by fordCourier »

Good luck with that Accel crap. :evil:

My trucks been down for a couple months, but is now back to life thanks to "Accel". Let me explain.

I kept having hard starting issues... installed a model L with an electric primer, to no avail. On my way back home on a 140 mile round trip, the truck started missing, and then dying altogether. After an obligitory down time of about 20-30 minutes it would restart. It got progressively worse as I went along, eventually only allowing about 20 miles before crapping out.

By the time I got home I was very worried, the truck was running badly and failed the "dollar bill" test- where you hold a dollar bill (or piece of paper) up to the exhaust pipe. If the exhaust pushes the dollar away, everythings okay. If it occasionally sucks it back IN then its evidence of a burned valve. I was convinced it was a burned valve- I added it up.

Increased ignition timing + lean mixture computer + old engine = burned valve. Hard starting had occured for a long while and I had gotten to my wits end. I threw in the towel.

So yesterday I decided to see if I could get it to run- and it did, around the block until it died. Turns out I had forgotten to open the liquid service valve (oops). Now I was a block from home and- yes- it wouldn't start.

I went through everything to no avail, and then I noticed it.

The Accel Super Coil was leaking a nearly invisible, very light mineral-type oil. It was all over the secondary terminals and running down the side of the engine compartment. I went home and grabbed the old OEM coil (that I was not sure worked, as I had dropped it on concrete while replacing it with the Accel and it had a big dent in the bottom corner) and replaced it. It worked- easy starts!

So good luck with Accel. One thing was the OEM mount for the coil was oriented sideways... I don't know if that made a difference. Another thing was the OEM bracket fairly sandwiches the coil to the ignition module which strikes me as kind of a bad idea (heat).

Other than that it starts even better than before all the problems began and I think it has a lot to do with the electric primer mounted on the model L- it supplies a shot of gas right underneath the valve daiphragm- you need a vac. pickoff there. Its wired in parallel with the ignition start circuit, so when I turn the key- bam! it starts right up. I found out about it from an eBay manual for Ford 2.3L granada near that time period. It showed a model L with the electric primer- the "Propane Guy" from Canada hooked me up with those parts.

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