stagefumer11 Posted March 7, 2006 Share Posted March 7, 2006 Unsure if the intake is a related problem. But ive installed a flowed and have intake manifold with a 60mm Sr20det throttle body. (bored intake to match) this was installed at the same time i did a head gasket on it. Now the head gasket is a long story but it ended up with the head being wapred and it had to come off again. Even with this intake installed with the warped head. It ran mint. Simply great smooth heaps of power. Now after getting the head skimmed. and crack tested. All installed. ect... IT runs like complete crap. Seems to be running lean alot of the time. any sign of boost after 2 seconds. bam... Lean!!!! Now gone thru the most common ideas that could be a problem e.g adjusting afm ? (only for non boost really) Checking timing. Also cam timing. ect... The question is. Can increasing your intake flow, with a bigger TB ect make it run megga lean?. or what can cause it to randomly after putting it back together that it all changes. Quote Link to comment Share on other sites More sharing options...
AK-Z Posted March 7, 2006 Share Posted March 7, 2006 Cam timing? Quote Link to comment Share on other sites More sharing options...
Drax240z Posted March 7, 2006 Share Posted March 7, 2006 Look for vacuum leaks at all? Sounds like one. Your TPS might be out of adjustment as well... Quote Link to comment Share on other sites More sharing options...
vashonz Posted March 7, 2006 Share Posted March 7, 2006 I think someone used the change in AFR as proof of an increase in flow of an aftermarket intake manifold. I think it was either lonewolf or speed shop thagard (one of them is james I think). Quote Link to comment Share on other sites More sharing options...
2126 Posted March 7, 2006 Share Posted March 7, 2006 Heres something to consider! You mentioned you had your head skimmed (shaved, milled, etc.)! How much did they remove to flatten her back out? When you remove material from the head, it lowers the head and effects the overall timing by actually allowing the cam sprocket/cam to rotate x degrees CCW (when viewed from the front of the engine). Slimming up the cam towers will compensate for the loss of head material. Just some food for thought! Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted March 7, 2006 Share Posted March 7, 2006 Did the shop add shims under the cam towers after the head shave? For every 1mm (0.040") you shave off the head, the cam is retarded 1.91 degrees relative to crankshaft. Of course the chain may have some slack to it in the first place that adds even more retard to give you problem. Check for vacuum leak and electrical connections first, sooo many engine problems turn out to be those small problems. Quote Link to comment Share on other sites More sharing options...
stagefumer11 Posted March 8, 2006 Author Share Posted March 8, 2006 When the head was skimmed its was minimal. Nothing big at all. I seem'd to found out a major part ofthe probem seemd to be a bad wire on the afm plug. *resoldierd* and alot of the leaning out probems were gone. Its still leaning out. not as bad tho. So i say ive maxed my injectors out. Since they are only 185cc's And having the extra flow of a 60mm tb and larger intake runners. well at 8psi they seem'd to be maxed. Got some vg30et inectors on the way. 259cc should help alot Quote Link to comment Share on other sites More sharing options...
78 280zcar Posted March 10, 2006 Share Posted March 10, 2006 I would just like to say hello, this is the first time I have posted on this site. I am having the same problem with my 78 after the throttle body upgrade and rebuilding the whole engine, only to have to take the head off again. I am thinking I may have to shim the towers or get bigger cc injectors. But let me know how the injector upgrade works for you. Quote Link to comment Share on other sites More sharing options...
dapiper Posted March 11, 2006 Share Posted March 11, 2006 Once an EFI engine is fuel mapped, any change of intake (larger) that adds mass will affect the charge air temp (heat soak) causing it to run lean. Retarding cam will make run rich, since engine will pull less air. Quote Link to comment Share on other sites More sharing options...
stagefumer11 Posted March 11, 2006 Author Share Posted March 11, 2006 figured so. thats the problem. Dfinity 4500rpm onwards it leans out. Injectors come in the next few days. would 259cc injectors compared to 180cc's Be enough ? Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted March 11, 2006 Share Posted March 11, 2006 Stock AFM? IIRC the stock AFM max out at 4000RPM or so, from that point on the ecu runs on a predetermined fuel map. With intake upgrade that allows more air, the predetermined fuel map cannot match the extra air....so it runs lean. EDIT to add : I noticed you are running a L20et. My comment above refers to L28et with flap door style AFM. Does your L20et run with a old style AFM or a Z31 style MAF? Quote Link to comment Share on other sites More sharing options...
george.bryant Posted March 12, 2006 Share Posted March 12, 2006 the L20et runs the same style AFM as the L28et, Z18et Quote Link to comment Share on other sites More sharing options...
stagefumer11 Posted March 12, 2006 Author Share Posted March 12, 2006 Correct the same as a l28et. the 4000rpm maxed on the AFM will explain it clearly. Cannot wait for the injectors now Quote Link to comment Share on other sites More sharing options...
george.bryant Posted March 13, 2006 Share Posted March 13, 2006 What injectors u gonna use? Quote Link to comment Share on other sites More sharing options...
george.bryant Posted March 13, 2006 Share Posted March 13, 2006 Can somebody show me a fuel/air map of a stock l28et ?? Why does it lean off at 4000rpm? Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted March 13, 2006 Share Posted March 13, 2006 Why does it lean off at 4000rpm? Because it is evil. Trap door afm measures air more correctly at low air flow because the air flow hit the door square on. After the door opens wide it cannot measure air as correctly anymore because air flow do not hit the trap door head on. Since the measurement is no longer very accurate at higher rpm, they opt to use a predetermined fuel map. The fuel map inside ECU makes you lean out. Quote Link to comment Share on other sites More sharing options...
george.bryant Posted March 13, 2006 Share Posted March 13, 2006 Grrr, so what to do? Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted March 13, 2006 Share Posted March 13, 2006 Different people different answers. Once my car is back together I'll start on the turbo motor. I will be using Z31 MAF(ditching the AFM outright) and reprogrammed '88 maxima ECU. Quote Link to comment Share on other sites More sharing options...
george.bryant Posted March 13, 2006 Share Posted March 13, 2006 88 maxima ecu has the same ecu plug as l series ecu? Quote Link to comment Share on other sites More sharing options...
Mack Posted March 13, 2006 Share Posted March 13, 2006 Yup. know htis problem all to well. more airflow above 3500RPM = L28E run lean under WOT. I've got a flat top block with a MN47 head and felpro gasket. 11.7:1 compression. I know I know, too much on crap gas, blah blah blah.... anyway, yes it detonates, but only above about 3500RPM. when that stock flapper door stays wide open, the ECU goes lean. especially with a 60MM TB, ported head, port matched intake with injector bumps removed, and a little bump in the cam department. I saw an A/F chart on a stock L28E onces, Ill have to find it again, ANYWAY, under WOT, the afr hit about 14.5:1 above about 3700rpm. that is NOT a ratio for optimum performance. the reason stock engines dont ping is because of the low compression ratio. not very sensative to lean mixtures. however, when you add 3 points of compression, it tends to make it a little more sensative to lean mixtures and detonation. If I could run a proper A/F ratio (like 13:1, optimum for performance) I could probably get by on 93 octane. the fix, you ask? run a different EFI set-up. turbo will actually MEASURE more air than an NA set-up will, Z31 will measure up to about 300rwhp before it goes linear, or MEgasquirt will get the job done as well. Quote Link to comment Share on other sites More sharing options...
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